Showing papers on "Base station published in 2004"

How much feedback is multi-user diversity really worth?

Abstract: Wireless scheduling algorithms can extract multi-user diversity (MUDiv) via prioritizing the users with best current channel conditions. One drawback of MUDiv is the required feedback carrying the instantaneous channel rates from from all active subscribers to the access point/base station. This paper shows that this feedback load is, for the most part, unjustified. To alleviate this problem, we propose a technique allowing to dramatically reduce the feedback (by up to 90%) needs while preserving the essential of the scheme performance. We provide a theoretical analysis of the feedback load as function of the system's ergodic and outage capacity for both the traditional MUDiv scheme and the new scheme.

Least squares algorithms for time-of-arrival-based mobile location

Abstract: Localization of mobile phones is of considerable interest in wireless communications. In this correspondence, two algorithms are developed for accurate mobile location using the time-of-arrival measurements of the signal from the mobile station received at three or more base stations. The first algorithm is an unconstrained least squares (LS) estimator that has implementation simplicity. The second algorithm solves a nonconvex constrained weighted least squares (CWLS) problem for improving estimation accuracy. It is shown that the CWLS estimator yields better performance than the LS method and achieves both the Crame/spl acute/r-Rao lower bound and the optimal circular error probability at sufficiently high signal-to-noise ratio conditions.

Context caching using neighbor graphs for fast handoffs in a wireless network

Abstract: User mobility in wireless data networks is increasing because of technological advances, and the desire for voice and multimedia applications. These applications, however, require fast handoffs between base stations to maintain the quality of the connections. Previous work on context transfer for fast handoffs has focused on reactive methods, i.e. the context transfer occurs after the mobile station has associated with the next base station or access router. In this paper, we describe the use of a novel and efficient data structure, neighbor graphs, which dynamically captures the mobility topology of a wireless network as a means for prepositioning the station's context ensuring that the station's context always remains one hop ahead. From experimental and simulation results, we find that the use of neighbor graphs reduces the layer 2 handoff latency due to reassociation by an order of magnitude from 15.37ms to 1.69ms, and that the effectiveness of the approach improves dramatically as user mobility increases.

El display and its driving method

Abstract: The invention relates to a method for terminal-assisted interference control in a mobile communication system employing multi-carrier techniques such as OFDM, the mobile communication system comprising a network (N) with a plurality of base stations (B1 to B3) controlled by a central entity (CE), and the base stations having means for communication with user terminals (T1 to T3) located inside their cell service area (C1 to C3). The central entity (CE) schedules time-frequency groups available, for data communication purposes between the terminals and the base station (B1 to B3), for the base stations under its control (B1 to 83) and for the terminals (T1 to T3) involved in the scheduling process. Scheduling decisions are made for each time interval (TI1 to TIn).

Generalized multiuser orthogonal space-division multiplexing

Abstract: This paper addresses the problem of performing orthogonal space-division multiplexing (OSDM) for downlink, point-to-multipoint communications when multiple antennas are utilized at the base station (BS) and (optionally) all mobile stations (MS). Based on a closed-form antenna weight solution for single-user multiple-input multiple-output communications in the presence of other receiver points, we devise an iterative algorithm that finds the multiuser antenna weights for OSDM in downlink or broadcast channels. Upon convergence, each mobile user will receive only the desired activated spatial modes with no cochannel interference. Necessary and sufficient conditions for the existence of OSDM among the number of mobile users, the number of transmit antennas at the BS, and the number of receive antennas at the MS, are also derived. The assumption for the proposed method is that the BS knows the channels for all MS's and that the channel dynamics are quasi-stationary.

System and method for automatically configuring and integrating a radio base station into an existing wireless cellular communication network with full bi-directional roaming and handover capability

Abstract: A radio base station in a mobile communication network collects information about the network and exchanges data with a configuration device, the Internet System Manager (iSM). The iSM automatically configures and integrates the base station into the network by defining configuration parameter settings that allow fill interoperation of the base station with the network, with regards to roaming and handover in particular, without the need to add or modify parameter settings in other existing network elements. A very large number and high geographical density of such base stations is supported with full interoperation between them, allowing to overcome limitations of conventional mobile communication networks in this regard, by utilizing a certain combination of parameter settings and a new method to address the different base stations in the network.

Base station based methods and apparatus for supporting break before make handoffs in a multi-carrier system

Abstract: A mobile communications device initiates a handoff from its current base station (BS) sector network attachment point to a new BS sector. The mobile sends a handoff request over its current wireless link to the current BS sector, which forwards the request to the new BS sector, e.g., via a network link. The new BS sector processes the request assigning dedicated resources, e.g., an identifier and dedicated uplink segments. Information identifying the allocated resources is conveyed from the new BS sector via the current BS sector to the mobile. The mobile determines the time of the allocated dedicated segments based upon a received beacon signal from the new BS sector with known timing relationships to dedicated segments. The mobile breaks the original wireless link just prior to the time of the first assigned dedicated segment. The mobile communicates information on the assigned dedicated segments to perform registration operations, e.g., timing synchronization and power control, establishing a new wireless link.

Proactive key distribution using neighbor graphs

Abstract: User mobility in wireless data networks is increasing because of technological advances, and the desire for voice and multimedia applications. These applications, however, require that handoffs between base stations (or access points) be fast to maintain the quality of the connections. In this article we introduce a novel data structure, the neighbor graph, that dynamically captures the mobility topology of a wireless network. We show how neighbor graphs can be utilized to obtain a 99 percent reduction in the authentication time of an IEEE 802.11 handoff (full EAP-TLS) by proactively distributing necessary key material one hop ahead of the mobile user. We also present a reactive method for fast authentication that requires only firmware changes to access points and hence can easily be deployed on existing wireless networks.

Method and system for wireless communication networks using cooperative relaying

Abstract: The present invention relates to relay supported wireless communication to enhance communication performance. In the wireless communication system according to the invention neighboring relay stations are arranged with substantially overlapping coverage. In the method according to the invention mobile stations makes soft association to relay stations. The mobile stations feed back the selection of relay stations and channel quality measures to the base station. The base station adapts the transmission to the relay stations based on each mobile stations reported soft associations and channel quality measures. In this way the control signaling to and from the relay stations can be very limited.

Micro-payment scheme encouraging collaboration in multi-hop cellular networks

Abstract: In a communication system having a number of base stations and user devices, a sending user device comprising a processor and a memory is configured to generate a packet or other communication for forwarding to a receiving user device via one or more intermediary user devices of the system The forwarding path of the communication may involve one or more of the base stations A payment token is associated with the communication, such that at least one of the intermediary user devices can generate a payment claim based on the payment token The payment token is independent of the particular identities of the one or more intermediary user devices of the system

Methods and apparatus of enhancing performance in wireless communication systems

Abstract: Methods and apparatus for supporting and using multiple communications channels corresponding to different transmit technologies and/or access technologies in parallel within a cell of a wireless communications system are described. Mobile nodes support multiple technologies and can switch between the technology being used at a particular point in time, e.g., from a first channel corresponding to a first technology to a second channel corresponding to a different technology which provides better transmission characteristics, e.g., a better perceived channel quality. Mobiles maintain at least two sets of channel quality information at any one point in time. Mobiles select the better channel and communicate the channel selection to the base station or communicate channel quality information for multiple channels to the base station and allow the base station to select the channel corresponding to the technology providing the better conditions for the mobile. Different mobiles in the same cell may support different technologies.

Intrusion tolerance and anti-traffic analysis strategies for wireless sensor networks

Abstract: Wireless sensor networks face acute security concerns in applications such as battlefield monitoring. A central point of failure in a sensor network is the base station, which acts as a collection point of sensor data. In this paper, we investigate two attacks that can lead to isolation or failure of the base station. In one set of attacks, the base station is isolated by blocking communication between sensor nodes and the base station, e.g. by DOS attacks. In the second attack, the location of the base station is deduced by analyzing data traffic towards the base station, which can lead to jamming and/or discovery and destruction of the base station. To defend against these attacks, two secure strategies are proposed. First, secure multi-path routing to multiple destination base stations is designed to provide intrusion tolerance against isolation of a base station. Second, anti-traffic analysis strategies are proposed to help disguise the location of the base station from eavesdroppers. A performance evaluation is provided for a simulated sensor network, as well as measurements of cryptographic overhead on real sensor nodes.

Method and System for Wireless Networking Using Coordinated Dynamic Spectrum Access

Abstract: A method and system for coordinated dynamic access to radio spectrum for wireless networking includes defining a coordinated access band (CAB) from which radio access network (RAN) managers may request spectrum allocations in the form of time bound spectrum leases for their respective requesting base stations. In one embodiment of the present invention, a DIMSUMnet architecture is implemented to make some fundamental choices and to centralize the collection of information, such as spectral occupancy, thermal and adjacent frequency interference. Such collected information is subsequently used by a spectrum broker in making spectrum allocation decisions. The DIMSUMnet architecture of the present invention also introduces a RAN manager element to centralize the task of acquiring time bound spectrum leases and for configuring the base stations.

Range extension without capacity penalty in cellular networks with digital fixed relays

Abstract: The concept of relaying is a promising solution for the challenging throughput and high data rate coverage requirements of future wireless cellular networks. In this paper, we demonstrate that the area that a single BS (base station) can provide high data rate coverage can significantly be increased by the employment of digital fixed relays without any penalty in capacity. This network architecture, which allows two-hop links, is expected to facilitate cost-efficient high data rate coverage in beyond-3G cellular wireless networks. In particular, we considered the downlink of a non-CDMA network where 6 digital fixed relays are placed around each BS in a hexagonal layout. The improved two-hop links can be exploited to yield higher throughput through the use of adaptive modulation and coding.

Time monitoring of packet retransmissions during soft handover

Abstract: The present invention relates to a method for scheduling data retransmissions, a method for use in a data retransmission scheme and a method for updating a soft buffer of a base station in a mobile communication system during a soft-handover. The present invention relates to a base station executing the controlling and updating method, a communication terminal for executing the scheduling method and to a mobile communication system comprising at least one the base station and communication terminal. To prevent erroneous combining of data packets in a packet retransmission scheme at the receiver, the present invention provides a method that may flush the soft buffer region associated to a received data packet upon its correct reception. Further, a method is provided that monitors the time elapsed since the last storing of a data packet in a buffer region of a base station to be able to trigger the flush of the buffer region upon expiry of a threshold time period.

Tdoa/gps hybrid wireless location system

Abstract: A method and system for enhancing the accuracy and robustness of locations determined for a mobile wireless transceiver (MS) in a cellular telephone communications system integrates location-related information both from an assisted GPS device embedded in the mobile unit and from infrastructure-based facilities that extract signal characteristic data at networked base stations (105). Available supporting collateral information may be additionally evaluated in the location determination to provide location estimates of enhanced robustness and accuracy.

Wireless communication system and method using multiple antennas

Abstract: A wireless communication system, and method using multiple antennas, includes a base station that applies predetermined weight vectors to multi-user signals and transmits the multi-user signals through a plurality of transmission antennas, and a plurality of mobile stations that receive and process the multi-user signals, wherein each mobile station includes a signal reception unit that processes the multi-user signals, and a feedback signal generation unit that estimates channel characteristics, over which the multi-user signals have been transmitted, from the multi-user signals, classifies a plurality of weight vectors to be applied to the estimated channel characteristics into a plurality of sets such that vectors orthogonal to one another are classified into a single set, selects a set maximizing a transmission capacity from among the classified sets, and feeds back weight indexes of weight vectors included in the selected set and weighted channel information to the base station.

Power-aware base station positioning for sensor networks

Abstract: We consider the problem of positioning data collecting base stations in a sensor network. We show that in general, the choice of positions has a marked influence on the data rate, or equivalently, the power efficiency, of the network. In our model, which is partly motivated by an experimental environmental monitoring system, the optimum data rate for a fixed layout of base stations can be found by a maximum flow algorithm. Finding the optimum layout of base stations, however, turns out to be an NP-complete problem, even in the special case of homogeneous networks. Our analysis of the optimum layout for the special case of the regular grid shows that all layouts that meet certain constraints are equally good. We also consider two classes of random graphs, chosen to model networks that might be realistically encountered, and empirically evaluate the performance of several base station positioning algorithms on instances of these classes. In comparison to manually choosing positions along the periphery of the network or randomly choosing them within the network, the algorithms tested find positions, which significantly improve the data rate and power efficiency of the network.

Methods and apparatus for performing handoffs in a multi-carrier wireless communications system

Abstract: A mobile communications device initiates a handoff from its current base station (BS) sector network attachment point to a new BS sector. The mobile sends a handoff request over its current wireless link to the current BS sector, which forwards the request to the new BS sector, e.g., via a network link. The new BS sector processes the request assigning dedicated resources, e.g., an identifier and dedicated uplink segments. Information identifying the allocated resources is conveyed from the new BS sector via the current BS sector to the mobile. The mobile determines the time of the allocated dedicated segments based upon a received beacon signal from the new BS sector with known timing relationships to dedicated segments. The mobile breaks the original wireless link just prior to the time of the first assigned dedicated segment. The mobile communicates information on the assigned dedicated segments to perform registration operations, e.g., timing synchronization and power control, establishing a new wireless link.

Using a derived table of signal strength data to locate and track a user in a wireless network

Abstract: A method for locating a user in a wireless network is disclosed. A mobile computer seeking to determine its location within a building detects the signal strength of one or more wireless base stations placed at known locations throughout the building. The mobile computer uses this measured signal strength to determine its location via a signal-strength-to-location table look-up. A table of known locations within the building and the base station signal strength at those locations is searched to find the most similar stored signal strength to the signal strength detected. The location corresponding to the most similar stored signal strength is determined to be the current location of the mobile computer. Alternatively, a number of signal strengths from the table can be used and the corresponding locations can be spatially averaged to determine the location of the mobile computer. The table can be derived empirically, by placing a mobile computer at the known locations and detecting the signal strength of the wireless base stations at those locations, or the table can be derived mathematically by taking into account a reference signal strength, the distance between the reference point and the known location, and the number of walls between the reference point and the known location. As an alternative, the base stations can detect the signal strength of the mobile computer. In such a case, the table would relate a known position of the mobile computer to the signal strength of the mobile computer at that location as detected by the one or more base stations.

System and method for interference mitigation for wireless communication

Abstract: Disclosed are systems and methods which provide interference mitigation by making alternative resources available within areas served by wireless communication links. Embodiments provide multiple channel availability in establishing wireless communication links to facilitate interference mitigation. Time domain techniques, spatial processing techniques, and/or frequency domain techniques may be implemented for spectrum management. Embodiments provide wireless base station configurations in which all or a plurality of base station sectors use a same frequency channel and/or in which each sector or a plurality of sectors use all frequency channels. Multi-channel strategies may be implemented such as to provide dynamic selection of a “best” frequency channel, to provide transmission of identical data on multiple channels for combining/selection at the receiver, and/or to provide for dividing the data for transmission on multiple channels.

Wireless communication system, server and mobile station therefor

Abstract: This invention provides a wireless communication system wherein a network to which a mobile station should be handed over can be selected, using parametric data collected from network components other than the mobile station. Time taken for a handover between different types of network systems is reduced. The wireless communication system of the present invention comprises a mobile station equipped with multiple wireless interfaces, a server connected to a fixed network, and multiple access points. The mobile station determines available wireless interfaces and sends notification of the available interfaces' identifiers to the server. The server collects managerial data from network components and selects a wireless interface, based on the notification from the mobile station and the managerial data. The mobile station registers its locations in visiting networks corresponding to multiple available wireless interfaces with the server. The server retains the registrations of mobile station locations for the above wireless interfaces.

Relation between base station characteristics and cost structure in cellular systems

Abstract: A simple method for estimating the costs of building and operating a cellular mobile network is proposed. Using the empirical data from a third generation mobile system (WCDMA), it is shown that the cost is driven by different factors depending on the characteristics of the base stations deployed. When the site density increased, the operational and transmission costs tend to dominate rather than the radio equipment and site costs. The results also show how, for different capacity requirements, the costs can be minimized by a proper selection of macro, micro and pico base stations. In many scenarios, the macro base stations yield the lowest cost, indicating that the coverage (cell range) is an important parameter when designing wireless systems.

Dual prediction-based reporting for object tracking sensor networks

Abstract: As one of the wireless sensor network killer applications, object tracking sensor networks (OTSNs) disclose many opportunities for energy-aware system design and implementations. We investigate prediction-based approaches for performing energy efficient reporting in OTSNs. We propose a dual prediction-based reporting mechanism (called DPR), in which both sensor nodes and the base station predict the future movements of the mobile objects. Transmissions of sensor readings are avoided as long as the predictions are consistent with the real object movements. DPR achieves energy efficiency by intelligently trading off multihop/long-range transmissions of sensor readings between sensor nodes and the base station with one-hop/short-range communications of object movement history among neighbor sensor nodes. We explore the impact of several system parameters and moving behavior of tracked objects on DPR performance, and also study two major components of DPR: prediction models and location models through simulations. Our experimental results show that DPR is able to achieve considerable energy savings under various conditions and outperforms existing reporting mechanisms.

On using peer-to-peer communication in cellular wireless data networks

Abstract: A recent class of approaches for enhancing the performance of cellular wireless data networks has focused on improving the underlying network model. It has been shown that using the peer-to-peer network model, a mode of communication typically seen in ad hoc wireless networks, can result in performance improvements such as increased data rate, reduced transmission power, better load balancing, and enhanced network coverage. However, the true impact of adopting the peer-to-peer network model in such an environment is yet to be fully understood. In this paper, we investigate the performance benefits and drawbacks of using the peer-to-peer network model for Internet access in cellular wireless data networks. We find that, although the peer-to-peer network model has significantly better spatial reuse characteristics, the improved spatial reuse does not translate into better throughput performance. Instead, we observe that using the peer-to-peer network model as-is might actually degrade the throughput performance of the network. We identify and discuss the reasons behind these observations. Using the insights gained through the performance evaluations, we then propose two categories of approaches to improve the performance of the peer-to-peer network model: approaches that leverage assistance from the base station and approaches that leverage the relaying capability of multihomed hosts. Through simulation results, we show that using the peer-to-peer network model in cellular wireless data networks is a promising approach when the network model is complemented with appropriate mechanisms.

Congestion control in a wireless data network

Abstract: Techniques for congestion control are disclosed. In one embodiment, a base station allocates (350) a shared resource using a combination of zero or more individual grants and zero or more common grants, and generates a busy signal (370) in response to loading conditions that exceed a pre-determined level. In another embodiment, a subset of transmitting mobile stations reduce their transmission rate in response to a busy signal. The subset may include autonomous transmission, commonly granted transmission, individually granted transmission, or any combination thereof. In various embodiments, rate adjustment may be probabilistic or deterministic. In one embodiment, a rate table (1000) is deployed, and a mobile station decreases or increases the transmission rate from one rate in the table to a lower or higher rate in the table, respectively, in response to the busy signal. Various other aspects are also presented. These aspects have the benefit of providing efficient congestion control, avoiding excessive interference and increasing capacity.

Method of retransmission protocol reset synchronisation

Abstract: A method of retransmission protocol reset synchronisation in a radio network of a communication system, said radio network including at least one radio network controller RNC for controlling a plurality of base stations in communication with mobile terminals, wherein the RNC communicates with a communication terminal using a radio link control RLC procedure and the plurality of base stations communicate with the mobile terminals using a medium access control MAC procedure, comprising the steps of initiating a RLC reset procedure upon occurrence of an unrecoverable protocol error and initiating a MAC reset procedure in response to a RLC reset procedure.

An adaptive scheme for vertical handoff in wireless overlay networks

Abstract: Vertical handoff is the switching process between heterogeneous wireless networks. Discovering the reachable wireless networks is the first step for vertical handoff. After discovering the reachable candidate networks, the mobile terminal decides whether to perform handoff or not. We present an adaptive scheme for vertical handoff in wireless overlay networks. Our system discovery method effectively discovers the candidate networks for the mobile terminal. Moreover, we propose two adaptive evaluation methods for the mobile terminal to determine the handoff time that relies on the candidates' resources and the running applications. The simulation results show that the proposed system discovery method can balance the power consumption and the system discovery time. Furthermore, the proposed handoff decision method can decide the appropriate time to perform handoff.

Filter technologies for wireless base stations

Abstract: Phenomenal growth in the telecommunication industry in recent years has brought significant advances in filter technology as new communication systems emerged, demanding more stringent filter characteristics. In particular, the growth of the wireless communication industry has spurred tremendous activity in the area of microwave filter miniaturization and has been responsible for many advances made in this field. The filters that are currently being used in wireless base stations can be divided into two main categories: coaxial cavity resonator filters and dielectric resonator (DR) filters. While coaxial cavity filters have limited quality factor (Q) values, they offer the lowest cost design and are still being widely employed, particularly in wide bandwidth applications. With increased demands for high performance wireless systems, dielectric resonator filters are emerging as the baseline design for wireless base stations. Over the next five years, dielectric resonator filters are expected to have a significant share of the overall wireless base station filter market. High-temperature superconductor (HTS) filters are also expected to have a share of this market, particularly for systems, which have very stringent requirements for out-of-band interference. In this article, we begin by reviewing the main filter requirements, highlighting the technologies that are being currently employed. Emerging filter technologies that have the potential to replace the existing technologies are then described.

Coordinated load balancing, handoff/cell-site selection, and scheduling in multi-cell packet data systems

Abstract: We investigate a wireless system of multiple cells, each having a downlink shared channel in support of high-speed packet data services. In practice, such a system consists of hierarchically organized entities including a central server, Base Stations (BSs), and Mobile Stations (MSs). Our goal is to improve global resource utilization and reduce regional congestion given asymmetric arrivals and departures of mobile users. For this purpose, we propose a scalable cross-layer framework to coordinate packet-level scheduling, call-level cell-site selection and handoff, and system-level loading balancing based on load, throughput, and channel measurements at different layers. In this framework, an opportunistic scheduling algorithm---the weighted Alpha-Rule---exploits multiuser diversity gain in each cell independently, trading aggregate (mean) downlink throughput for fairness and minimum rate guarantees among MSs. Each MS adapts to its channel dynamics and the load fluctuations in neighboring cells, in accordance with MSs' mobility and their arrivals or departures, by initiating load-aware handoff and cell-site selection. The central server adjusts the scheduling parameters of each cell to coordinate cells' coverage, or cell breathing, by prompting distributed MS handoffs. Across the whole system, BSs and MSs constantly monitor their load, throughput, or channel quality in order to facilitate the overall system coordination.Our specific contributions in such a framework are highlighted by the minimum-rate guaranteed Weighted Alpha-Rule scheduling, the load-aware MS handoff/cell-site selection, and the Media Access Control (MAC)-layer cell breathing. Our evaluations show that the proposed framework can improve the global resource utilization and load balancing, which translates into a smaller blocking rate of MS arrivals without extra resources, while the aggregate throughput remains roughly the same or improved around the hot-spots. Our tests also show that the coordinated system is robust to dynamic load fluctuations and is scalable to both system size and MS population.