Showing papers on "Base station published in 2012"

FemtoCaching: Wireless video content delivery through distributed caching helpers

Abstract: We suggest a novel approach to handle the ongoing explosive increase in the demand for video content in wireless/mobile devices. We envision femtocell-like base stations, which we call helpers, with weak backhaul links but large storage capacity. These helpers form a wireless distributed caching network that assists the macro base station by handling requests of popular files that have been cached. Due to the short distances between helpers and requesting devices, the transmission of cached files can be done very efficiently.

Argos: practical many-antenna base stations

Abstract: Multi-user multiple-input multiple-output theory predicts manyfold capacity gains by leveraging many antennas on wireless base stations to serve multiple clients simultaneously through multi-user beamforming (MUBF). However, realizing a base station with a large number antennas is non-trivial, and has yet to be achieved in the real-world. We present the design, realization, and evaluation of Argos, the first reported base station architecture that is capable of serving many terminals simultaneously through MUBF with a large number of antennas (M >> 10). Designed for extreme flexibility and scalability, Argos exploits hierarchical and modular design principles, properly partitions baseband processing, and holistically considers real-time requirements of MUBF. Argos employs a novel, completely distributed, beamforming technique, as well as an internal calibration procedure to enable implicit beamforming with channel estimation cost independent of the number of base station antennas. We report an Argos prototype with 64 antennas and capable of serving 15 clients simultaneously. We experimentally demonstrate that by scaling from 1 to 64 antennas the prototype can achieve up to 6.7 fold capacity gains while using a mere 1/64th of the transmission power.

Enabling Wireless Power Transfer in Cellular Networks: Architecture, Modeling and Deployment

Abstract: Microwave power transfer (MPT) delivers energy wirelessly from stations called power beacons (PBs) to mobile devices by microwave radiation. This provides mobiles practically infinite battery lives and eliminates the need of power cords and chargers. To enable MPT for mobile charging, this paper proposes a new network architecture that overlays an uplink cellular network with randomly deployed PBs for powering mobiles, called a hybrid network. The deployment of the hybrid network under an outage constraint on data links is investigated based on a stochastic-geometry model where single-antenna base stations (BSs) and PBs form independent homogeneous Poisson point processes (PPPs) and single-antenna mobiles are uniformly distributed in Voronoi cells generated by BSs. In this model, mobiles and PBs fix their transmission power at p and q, respectively; a PB either radiates isotropically, called isotropic MPT, or directs energy towards target mobiles by beamforming, called directed MPT. The model is applied to derive the tradeoffs between the network parameters including p, q, and the BS/PB densities under the outage constraint. First, consider the deployment of the cellular network. It is proved that the outage constraint is satisfied so long as the product the BS density decreases with increasing p following a power law where the exponent is proportional to the path-loss exponent. Next, consider the deployment of the hybrid network assuming infinite energy storage at mobiles. It is shown that for isotropic MPT, the product between q, the PB density, and the BS density raised to a power proportional to the path-loss exponent has to be above a given threshold so that PBs are sufficiently dense; for directed MPT, a similar result is obtained with the aforementioned product increased by the array gain. Last, similar results are derived for the case of mobiles having small energy storage.

Achieving "Massive MIMO" Spectral Efficiency with a Not-so-Large Number of Antennas

Abstract: Time-Division Duplexing (TDD) allows to estimate the downlink channels for an arbitrarily large number of base station antennas from a finite number of orthogonal uplink pilot signals, by exploiting channel reciprocity. Based on this observation, a recently proposed "Massive MIMO" scheme was shown to achieve unprecedented spectral efficiency in realistic conditions of distance-dependent pathloss and channel coherence time and bandwidth. The main focus and contribution of this paper is an improved Network-MIMO TDD architecture achieving spectral efficiencies comparable with "Massive MIMO", with one order of magnitude fewer antennas per active user per cell (roughly, from 500 to 50 antennas). The proposed architecture is based on a family of Network-MIMO schemes defined by small clusters of cooperating base stations, zero-forcing multiuser MIMO precoding with suitable inter-cluster interference mitigation constraints, uplink pilot signals allocation and frequency reuse across cells. The key idea consists of partitioning the users into equivalence classes, optimizing the Network-MIMO scheme for each equivalence class, and letting a scheduler allocate the channel time-frequency dimensions to the different classes in order to maximize a suitable network utility function that captures a desired notion of fairness. This results in a mixed-mode Network-MIMO architecture, where different schemes, each of which is optimized for the served user equivalence class, are multiplexed in time-frequency. In order to carry out the performance analysis and the optimization of the proposed architecture in a systematic and computationally efficient way, we consider the large-system regime where the number of users, the number of antennas, and the channel coherence block length go to infinity with fixed ratios.

Pilot contamination precoding in multi-cell large scale antenna systems

Abstract: An LSAS entails a large number (tens or hundreds) of base station antennas serving a much smaller number of terminals, with large gains in spectral-efficiency and energy-efficiency compared with conventional MIMO technology. Until recently it was believed that in multi-cellular LSAS, even in the asymptotic regime, as the number of service antennas tends to infinity, the performance is limited by directed inter-cellular interference. The interference results from unavoidable re-use of reverse-link pilot sequences (pilot contamination) by terminals in different cells. We devise a new concept that leads to the effective elimination of inter-cell interference in TDD LSAS systems. This is achieved by outer multi-cellular pre-coding, which we call pilot contamination pre-coding (PCP). The main idea of PCP is that each base station linearly combines messages aimed to terminals from different cells that re-use the same pilot sequence. Crucially, the combining coefficients depend only on the slow-fading coefficients between the terminals and the base stations. Each base station independently transmits its PCP-combined symbols using conventional linear pre-coding that is based on estimated fast-fading coefficients. Further we derive estimates for SINRs and a capacity lower bound for the case of LSASs with PCP and finite number of antennas M.

Distribution of Downlink SINR in Heterogeneous Cellular Networks

Abstract: The Signal to Interference Plus Noise Ratio (SINR) on a wireless link is an important basis for consideration of outage, capacity, and throughput in a cellular network. It is therefore important to understand the SINR distribution within such networks, and in particular heterogeneous cellular networks, since these are expected to dominate future network deployments . Until recently the distribution of SINR in heterogeneous networks was studied almost exclusively via simulation, for selected scenarios representing pre-defined arrangements of users and the elements of the heterogeneous network such as macro-cells, femto-cells, etc. However, the dynamic nature of heterogeneous networks makes it difficult to design a few representative simulation scenarios from which general inferences can be drawn that apply to all deployments. In this paper, we examine the downlink of a heterogeneous cellular network made up of multiple tiers of transmitters (e.g., macro-, micro-, pico-, and femto-cells) and provide a general theoretical analysis of the distribution of the SINR at an arbitrarily-located user. Using physically realistic stochastic models for the locations of the base stations (BSs) in the tiers, we can compute the general SINR distribution in closed form. We illustrate a use of this approach for a three-tier network by calculating the probability of the user being able to camp on a macro-cell or an open-access (OA) femto-cell in the presence of Closed Subscriber Group (CSG) femto-cells. We show that this probability depends only on the relative densities and transmit powers of the macro- and femto-cells, the fraction of femto-cells operating in OA vs. Closed Subscriber Group (CSG) mode, and on the parameters of the wireless channel model. For an operator considering a femto overlay on a macro network, the parameters of the femto deployment can be selected from a set of universal curves.

Channel measurements and analysis for very large array systems at 2.6 GHz

Abstract: Very large MIMO is a technique that potentially can offer large network capacities in multi-user scenarios where the users are equipped only with single antennas. In this paper we are investigating channel properties for a realistic, though somewhat extreme, outdoor base station scenario using a large array. We present measurement results using a 128 element linear array base station and 26 different user position in line-of-sight (LOS) and 10 different user position in non line-of-sight (NLOS). We analyze the Ricean K-factor, received power levels over the array, antenna correlation and eigenvalue distributions. We show that the statistical properties of the received signal vary significantly over the large array. Near field effects and the non-stationarities over the array help decorrelating the channel for different users, thereby providing a favorable channel conditions with stable channels and low interference for the considered single antenna users.

Network MIMO With Linear Zero-Forcing Beamforming: Large System Analysis, Impact of Channel Estimation, and Reduced-Complexity Scheduling

Abstract: We consider the downlink of a multicell system with multiantenna base stations and single-antenna user terminals, arbitrary base station cooperation clusters, distance-dependent propagation pathloss, and general “fairness” requirements. Base stations in the same cooperation cluster employ joint transmission with linear zero-forcing beamforming, subject to sum or per-base station power constraints. Intercluster interference is treated as noise at the user terminals. Analytic expressions for the system spectral efficiency are found in the large-system limit where both the numbers of users and antennas per base station tend to infinity with a given ratio. In particular, for the per-base station power constraint, we find new results in random matrix theory, yielding the squared Frobenius norm of submatrices of the Moore-Penrose pseudo-inverse for the structured non-i.i.d. channel matrix resulting from the cooperation cluster, user distribution, and path-loss coefficients. The analysis is extended to the case of nonideal Channel State Information at the Transmitters obtained through explicit downlink channel training and uplink feedback. Specifically, our results illuminate the trade-off between the benefit of a larger number of cooperating antennas and the cost of estimating higher-dimensional channel vectors. Furthermore, our analysis leads to a new simplified downlink scheduling scheme that preselects the users according to probabilities obtained from the large-system results, depending on the desired fairness criterion. The proposed scheme performs close to the optimal (finite-dimensional) opportunistic user selection while requiring significantly less channel state feedback, since only a small fraction of preselected users must feed back their channel state information.

Method and apparatus for short handover latency in wireless communication system using beam forming

Abstract: Beam selection is provided. A method for handover in a mobile station includes sending a scan request message for scanning a downlink (DL) beam with respect to a serving base station (BS) and a neighboring BS, to the serving BS, and receiving a scan response message; determining the DL beam for the MS by performing scanning with the serving BS and the neighboring BS based on the scan response message; sending a scan report message comprising a result of the scanning to the serving BS; when receiving an air-HO request message from the serving BS, generating an air-HO response message comprising information of a neighboring BS to which the MS hands over based on the air-HO request message; performing beam selection with the neighboring BS of the handover based on the air-HO request message; and performing the handover.

CloudIQ: a framework for processing base stations in a data center

Abstract: The cellular industry is evaluating architectures to distribute the signal processing in radio access networks One of the options is to process the signals of all base stations on a shared pool of compute resources in a central location In this centralized architecture, the existing base stations will be replaced with just the antennas and a few other active RF components, and the remainder of the digital processing including the physical layer will be carried out in a central location This model has potential benefits that include a reduction in the cost of operating the network due to fewer site visits, easy upgrades, and lower site lease costs, and an improvement in the network performance with joint signal processing techniques that span multiple base stations Further there is a potential to exploit variations in the processing load across base stations, to pool the base stations into fewer compute resources, thereby allowing the operator to either reduce energy consumption by turning the remaining processors off or reducing costs by provisioning fewer compute resources We focus on this aspect in this paperSpecifically, we make the following contributions in the paper Based on real-world data, we characterise the potential savings if shared homogeneous compute resources are used to process the signals from multiple base stations in the centralized architecture We show that the centralized architecture can potentially result in savings of at least 22 % in compute resources by exploiting the variations in the processing load across base stations These savings are achievable with statistical guarantees on successfully processing the base station's signals We also design a framework that has two objectives: (i) partitioning the set of base stations into groups that are simultaneously processed on a shared homogeneous compute platform for a given statistical guarantee, and (ii) scheduling the set of base stations allocated to a platform in order to meet their real-time processing requirements This partitioning and scheduling framework saves up to 19 % of the compute resources for a probability of failure of one in 100 million We refer to this solution as CloudIQ Finally we implement and extensively evaluate the CloudIQ framework with a 3GPP compliant implementation of 5 MHz LTE

Flexible power modeling of LTE base stations

Abstract: With the explosion of wireless communications in number of users and data rates, the reduction of network power consumption becomes more and more critical. This is especially true for base stations which represent a dominant share of the total power in cellular networks. In order to study power reduction techniques, a convenient power model is required, providing estimates of the power consumption in different scenarios. This paper proposes such a model, accurate but simple to use. It evaluates the base station power consumption for different types of cells supporting the 3GPP LTE standard. It is flexible enough to enable comparisons between state-of-the-art and advanced configurations, and an easy adaptation to various scenarios. The model is based on a combination of base station components and sub-components as well as power scaling rules as functions of the main system parameters.

Dynamic uplink-downlink configuration and interference management in TD-LTE

Abstract: Transmissions in different cells of a time-division duplex system are typically synchronous in order to eliminate the base station-to-base station and terminal-to-terminal interference. The synchronous operation limits dynamic resource configuration for downlink and uplink transmissions. Today, as a large percentage of mobile traffic is generated in hotspots and indoor environments, heterogeneous networks comprising high-power/wide-area and low-power/local-area network nodes are becoming a reality. Such heterogeneous networks provide opportunities to exploit dynamic uplink-downlink configuration in TDD systems, adapting to the individual traffic needs of a specific cell area. This article presents a tutorial overview of dynamic uplink-downlink configuration and interference management in time-division Long Term Evolution, including motivations, target deployment scenarios, opportunities and challenges, system requirements, design aspects, and performance evaluations.

Methods and systems for wireless networks with relays

Abstract: Methods and systems are provided for use with wireless networks having one or more cell in which each cell includes a base station (BS), at least one relay station (RS) and at least one mobile station (MS). The at least one relay station can be used as an intermediate station for providing communication between the BS and MS. Methods are provided for allocating OFDM resources for communicating between the BS, RS and/or MS for example dividing transmission resources into uplink and downlink transmissions and methods of inserting pilot symbols into transmission resources used by the RS. In some embodiments on the invention, the methods are consistent and/or can be used in conjunction with existing standards such as 802.16e.

Method and apparatus for measuring interference in wireless communication system

Abstract: An interference measurement method of a terminal is provided for facilitating downlink transmission in the mobile communication system based on Distributed Antenna System (DAS) in which multiple antennas controlled by a base station are distributed within the service area of the base station. The interference measurement method includes receiving channel measurement information and interference measurement information from a base station, receiving channel state information reference signals, calculating, when the received channel state information reference signal is for channel measurement, a received signal energy based on the channel measurement information and, when the received channel state information reference signal is for interference measurement, an interference based on the interference measurement information, generating channel quality information based on the received signal energy and the interference, and transmitting the channel quality information to the base station.

Base-station assisted device-to-device communications for high-throughput wireless video networks

Abstract: We propose a new scheme for increasing the throughput of video files in cellular communications systems. This scheme exploits (i) the redundancy of user requests as well as (ii) the considerable storage capacity of smartphones and tablets. Users cache popular video files and — after receiving requests from other users — serve these requests via device-to-device localized transmissions. We investigate what is the optimal collaboration distance, trading off frequency reuse with the probability of finding a requested file within the collaboration distance. We show that an improvement of spectral efficiency of one to two orders of magnitude is possible, even if there is not very high redundancy in video requests.

Methods and systems for controlling handovers in a co-channel network

Abstract: At least one example embodiment discloses a method of controlling a handover of a user equipment (UE) from a serving base station to a target, base station in a heterogeneous network. The method includes determining, by a serving base station, a speed of the UE and a type of the handover, the type of the handover being one of macro cell to macro cell, macro cell to small cell, small cell to macro cell and small cell to small cell, and controlling, by the serving base station, the handover from the serving base station to the target base station based on the speed of the UE and the type of handover.

Inter-device communication in wireless communication systems

Abstract: Systems, methods, and apparatuses for inter-device communication in wireless communication systems are provided. A user equipment (UE) may communicate directly with another UE over a direct inter-device communication link when they are located in proximity. The UE may simultaneously maintain an active communication link with its serving base station while communicating with other UEs over the inter-device communication link. Long term evolution (LTE) downlink or uplink radio resources may be used for communications over the inter-device communication link. Further, radio link parameters may be chosen specifically for the inter-device communication link.

Target cell selection for multimedia broadcast multicast service continuity

Abstract: Transfer of Multimedia Broadcast/Multicast Services (MBMS) over a Single Frequency Network (MBSFN) service and idle mode unicast service for a mobile entity from a source base station to a target base station may be managed by a base station or mobile entity of a cellular wireless communications system (WCS). Operations related to the transfer may include obtaining an MBMS status of the mobile entity, and/or obtaining MBMS support information for the base station. A network entity may facilitate MBMS discovery by a mobile entity, by transmitting a data element to the mobile entity including service identifiers mapped to corresponding cell identifiers to indicate respective MBMS services to be broadcast in an WCS area on adjacent cells identified by respective ones of the cell identifiers. The MBMS services may be broadcast within the WCS area using the adjacent cells previously indicated in the data element.

User equipment and power control method for random access

Abstract: An improved power control method and apparatus of a mobile terminal is provided for facilitating random access procedure in a mobile communication system based on a distributed antenna system. A method includes receiving, by the terminal, system information from a base station, the system information including transmit power information for transmitting a random access preamble; calculating a transmit power using the transmit power information; and transmitting the random access preamble using with the calculated transmit power.

System and method for peer-to-peer communication in cellular systems

Abstract: Systems and methods are provided for delivering both PMP communications, for example standard cellular communications via a base station, and also delivering P2P communications, for example, communications between two mobile stations, using the same spectral resources for both types of communication.

Measured propagation characteristics for very-large MIMO at 2.6 GHz

Abstract: Very-large multiple-input multiple-output (MIMO), also called massive MIMO, is a new technique that potentially can offer large network capacities in multi-user scenarios, where the base stations are equipped with a large number of antennas simultaneously serving multiple single-antenna users on the same frequency. We investigate channel behavior for a realistic outdoor base station scenario using large arrays. Specifically we compare dirty-paper coding (DPC) capacities and zero-forcing (ZF) sum-rates when using a physically large linear array and a compact cylindrical array, both having 128 antenna elements. As a base-line reference, we use the DPC capacity and ZF sum-rate for the ideal case with independent and identically distributed (i.i.d.) channel coefficients. The investigation shows that the measured channels, for both array types, often allow us to harvest most of the capacities/sum-rates achieved in the i.i.d. case, already at about 10 base station antennas per user.

PAR-Aware Large-Scale Multi-User MIMO-OFDM Downlink

Abstract: We investigate an orthogonal frequency-division multiplexing (OFDM)-based downlink transmission scheme for large-scale multi-user (MU) multiple-input multiple-output (MIMO) wireless systems. The use of OFDM causes a high peak-to-average (power) ratio (PAR), which necessitates expensive and power-inefficient radio-frequency (RF) components at the base station. In this paper, we present a novel downlink transmission scheme, which exploits the massive degrees-of-freedom available in large-scale MU-MIMO-OFDM systems to achieve low PAR. Specifically, we propose to jointly perform MU precoding, OFDM modulation, and PAR reduction by solving a convex optimization problem. We develop a corresponding fast iterative truncation algorithm (FITRA) and show numerical results to demonstrate tremendous PAR-reduction capabilities. The significantly reduced linearity requirements eventually enable the use of low-cost RF components for the large-scale MU-MIMO-OFDM downlink.

Coverage and Economy of Cellular Networks with Many Base Stations

Abstract: The performance of a cellular network can be significantly improved by employing many base stations (BSs), which shortens transmission distances. However, there exist no known results on quantifying the performance gains from deploying many BSs. To address this issue, we adopt a stochastic-geometry model of the downlink cellular network and analyze the mobile outage probability. Specifically, given Poisson distributed BSs, the outage probability is shown to diminish inversely with the increasing ratio between the BS and mobile densities. Furthermore, we analyze the optimal tradeoff between the performance gain from increasing the BS density and the resultant network cost accounting for energy consumption, BS hardware and backhaul cables. The optimal BS density is proved to be proportional to the square root of the mobile density and the inverse of the square root of the cost factors considered.

Method and apparatus for uplink power control in wireless communication system

Abstract: A method and an apparatus for uplink power control in a wireless communication system are provided. More specially, a method is provided in which a first base station in a wireless communication system periodically measures interference for a cell of a second base station neighboring the first base station, determines an average of the periodically measured interference, broadcasts the determined average of the periodically measured interference to mobile terminals located in a cell of the first base station, determines a weight for the determined average of the periodically measured interference, based on one of resource allocation information for the cell of the second base station and whether a specific message for interference regulation is received from the second base station, and transmits the determined weight to the mobile terminals.

Overview of Wireless Sensor Network

Abstract: Wireless Sensor Networks (WSNs) can be defined as a self-configured and infrastructureless wireless networks to monitor physical or environmental conditions, such as temperature, sound, vibration, pressure, motion or pollutants and to cooperatively pass their data through the network to a main location or sink where the data can be observed and analysed. A sink or base station acts like an interface between users and the network. One can retrieve required information from the network by injecting queries and gathering results from the sink. Typically a wireless sensor network contains hundreds of thousands of sensor nodes. The sensor nodes can communicate among themselves using radio signals. A wireless sensor node is equipped with sensing and computing devices, radio transceivers and power components. The individual nodes in a wireless sensor network (WSN) are inherently resource constrained: they have limited processing speed, storage capacity, and communication bandwidth. After the sensor nodes are deployed, they are responsible for self-organizing an appropriate network infrastructure often with multi-hop communication with them. Then the onboard sensors start collecting information of interest. Wireless sensor devices also respond to queries sent from a “control site” to perform specific instructions or provide sensing samples. The working mode of the sensor nodes may be either continuous or event driven. Global Positioning System (GPS) and local positioning algorithms can be used to obtain location and positioning information. Wireless sensor devices can be equipped with actuators to “act” upon certain conditions. These networks are sometimes more specifically referred as Wireless Sensor and Actuator Networks as described in (Akkaya et al., 2005).

Wireless Radio Extension Using Up- and Down-Conversion

Abstract: A system may include a base station and a remote radio head (“RRH”). The base station may receive digital data streams destined for a user device, and generate a first set of modulated signals. The modulated signals may each be based on a different one of the digital data streams. The generated first set of modulated signals may be modulated within a first carrier frequency band. The base station may output the first set of modulated signals to the RRH. The RRH may generate a second set of modulated signals based on the first set of modulated signals. The second set of modulated signals being modulated within a second carrier frequency band, and may output the second set of modulated signals to the user device.

Measurements and Modelling of Base Station Power Consumption under Real Traffic Loads

Abstract: Base stations represent the main contributor to the energy consumption of a mobile cellular network. Since traffic load in mobile networks significantly varies during a working or weekend day, it is important to quantify the influence of these variations on the base station power consumption. Therefore, this paper investigates changes in the instantaneous power consumption of GSM (Global System for Mobile Communications) and UMTS (Universal Mobile Telecommunications System) base stations according to their respective traffic load. The real data in terms of the power consumption and traffic load have been obtained from continuous measurements performed on a fully operated base station site. Measurements show the existence of a direct relationship between base station traffic load and power consumption. According to this relationship, we develop a linear power consumption model for base stations of both technologies. This paper also gives an overview of the most important concepts which are being proposed to make cellular networks more energy-efficient.

Relay Placement for Physical Layer Security: A Secure Connection Perspective

Abstract: This work studies the problem of secure connection in cooperative wireless communication with two relay strategies, decode-and-forward (DF) and randomize-and-forward (RF). The four-node scenario and cellular scenario are considered. For the typical four-node (source, destination, relay, and eavesdropper) scenario, we derive the optimal power allocation for the DF strategy and find that the RF strategy is always better than the DF to enhance secure connection. In cellular networks, we show that without relay, it is difficult to establish secure connections from the base station to the cell edge users. The effect of relay placement for the cell edge users is demonstrated by simulation. For both scenarios, we find that the benefit of relay transmission increases when path loss becomes severer.