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Smart Antennas (WSA), 2012 International ITG Workshop on

Date 7-8 March 2012

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Displaying Results 1 - 25 of 58
  • [Copyright notice]

    Page(s): i
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    Freely Available from IEEE
  • Program

    Page(s): ii - ix
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    Freely Available from IEEE
  • Channel prediction in multiple antenna systems

    Page(s): 1 - 7
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (433 KB) |  | HTML iconHTML  

    Techniques to predict the channel transfer functions into time direction and into frequency direction in multiple antenna systems are investigated in this paper. Having full channel state information at the receiver side and at the transmitter side in a mobile radio system is crucial for many sophisticated transmission techniques. Unfortunately, only channel state information at the receiver side can be estimated based on the transmission of a priori known training signals. This estimated channel state information cannot be directly reused as channel state information at the transmitter. Due to the use of different frequency bands in frequency division duplex systems, the estimated receiver side channel state information differs significantly from the transmitter side channel state information. Furthermore, due to the delay between estimating the receiver side channel state information and using this information at the transmitter side, the estimated receiver side channel state information can often not be directly reused in time division duplex systems. Thus, a prediction is appropriated. In time division duplex systems only a prediction into time direction is relevant. In frequency division duplex systems a prediction into frequency direction and potentially also a prediction into time direction are relevant. This paper shows different techniques to perform the prediction of the estimated receiver side channel state information to achieve transmitter side channel state information in multiple antenna systems. Channel measurements were conducted in a typical indoor scenario in order to evaluate the performance of the proposed prediction techniques. View full abstract»

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  • Low cost beam switchable reflectarray antenna

    Page(s): 8 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (337 KB) |  | HTML iconHTML  

    This paper presents a methodology for designing low cost beam switchable reflectarray antenna. An electronically beam steering antenna, which has a small section, is used to feed a printed reflectarray. Different functional regions were allocated on the printed reflectarray. By controlling the beam from the feed and illuminating each functional region separately, the beam from the reflectarray can be steered. To reduce the size of the feeding antenna, an folded dipole electronically steerable parasitic array radiator (ESPAR) antenna is designed. Compared with standard half-wavelength dipole antenna, the height of the folded dipole ESPAR antenna has been reduced by 50%. The beam from the folded dipole ESPAR antenna can be steered from - 50° to + 50°electronically. To validate this method, a prototype that can switch between three different beams has been constructed. View full abstract»

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  • CoMP in heterogeneous networks: A joint cooperative resource allocation approach

    Page(s): 12 - 19
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB) |  | HTML iconHTML  

    Coordinated multipoint transmission (CoMP) is considered for a heterogeneous network where different kinds of base stations (BS) are located. We focus on linear transceiver design including user scheduling with the goal of maximizing the weighted sum rate in the downlink of a multiple-input multiple-output orthogonal frequency division multiple access (MIMO-OFDMA) system, where each subchannel is allocated to a single user. Since the optimal solutions are extremely computationally complex to obtain, we propose a suboptimal joint resource allocation algorithm with a lower overall complexity. The proposed algorithm is able to take various linear power constraints into account, and simulation results indicate that using the proposed method achieves near-optimal solutions. View full abstract»

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  • Performance comparison of different protocols for a two-hop multiple relay network

    Page(s): 20 - 27
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (410 KB) |  | HTML iconHTML  

    Optimal resource allocation requires global channel knowledge in a relay network. When no or partial channel knowledge is available then static resource allocation is another alternative. This paper investigates the performances of different relaying protocols for static and dynamic resource allocations. A 2-hop relay network with multiple relays is considered. The protocols include adaptive amplify-or-decode & forward (ADF), coded cooperation (CC), and a novel method adaptive coded cooperation or amplify-and-forward (CCAF). In ADF and CCAF, a relay can adapt the forwarding scheme according to the reliability of the received signal. The results show that for fixed resource allocation, ADF always outperform CC. However, for dynamic resource allocation it is the other way around. Moreover, under dynamic resource allocation, CCAF and CC deliver similar performance. View full abstract»

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  • A distributed interference-aware load balancing algorithm for LTE multi-cell networks

    Page(s): 28 - 35
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (561 KB) |  | HTML iconHTML  

    Within a cellular wireless network the unbalanced user load among cells, together with Inter-Cell-Interference (ICI), constitute major factors responsible for poor overall performance. In the current work, a novel decentralized algorithm for Load Balancing in the downlink is suggested. Two are the major novelties in the analysis. (A) The algorithm is based on the solution of a mixed integer optimization problem solved using Lagrangian but not Linear Programming relaxation, which allows the solution to be binary for the user assignment variables. (B) Its implementation is based on exchange of certain prices among base stations and allows each of them to make choices individually without the aid of a central controller. The cell handover parameters are further adequately adjusted to enforce cell-edge users to migrate to their optimal base station. The algorithm aims at optimally balancing the load, while at the same time guaranteeing low levels of ICI. Its performance is evaluated through simulations, which illustrate the improvements provided on aggregate system utility. View full abstract»

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  • Multi-branch tomlinson-harashima precoding for single-user MIMO systems

    Page(s): 36 - 40
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (153 KB) |  | HTML iconHTML  

    Based on a multi-branch (MB) strategy, a new Tomlinson-Harashima precoding (THP) structure is proposed for single-user multiple-input multiple-output (SU-MIMO) systems, which offers a significant performance improvement compared to the conventional THP reported in the literature. The parallelized multiple branch signals are generated at the transmit side according to the pre-designed transmit patterns. An appropriate measurement metric is developed to select the best branch for transmission. Simulation results show that the proposed MB-THP precoder has a better bit error rate (BER) performance than the conventional THP. View full abstract»

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  • Performance analysis of LTE downlink under Symbol Timing Offset

    Page(s): 41 - 45
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB) |  | HTML iconHTML  

    In this paper, we evaluate the performance of a standardized OFDM system, namely Long Term Evolution (LTE) downlink, with imperfect symbol timing. A closed form expression of the post-equalization Signal to Interference and Noise Ratio (SINR) is derived and compared with results obtained from a standard compliant simulator. Also, we analyzed the channel estimation performance when Symbol Timing Offset (STO) occurs. This work reveals the impact of imperfect synchronization on the link performance. It also allows an accurate and realistic modeling of the physical layer behavior, which can be applied to reproduce results from time-consuming link level simulations. View full abstract»

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  • Robust transmit strategies for multiantenna bidirectional broadcast channels

    Page(s): 46 - 53
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (820 KB) |  | HTML iconHTML  

    In this work the multiantenna bidirectional broadcast channel under channel uncertainty is studied. This problem is motivated by the broadcast phase of the decode-and-forward bidirectional relaying protocol, where a relay node establishes a bidirectional communication between two other nodes while having only imperfect channel state information available. Different uncertainty models are investigated, where the nominal channels experience either a multiplicative or additive perturbation based on a spectral norm constraint. For these uncertainty models the corresponding capacity regions of the multiantenna bidirectional broadcast channel are analyzed. Further, robust transmit strategies are characterized and worst-case perturbations are identified. View full abstract»

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  • On energy efficiency of joint transmission coordinated multi-point in LTE-advanced

    Page(s): 54 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1097 KB) |  | HTML iconHTML  

    Coordinated Multi-Point (CoMP) transmission by neighboring base stations to mobile users is recently considered for both the cell-edge and the overall system throughput enhancements in next-generation cellular systems. As one of the most promising CoMP techniques, Joint Transmission (JT)-CoMP achieves higher spectral efficiency by exploiting cooperative diversity gains and inter-cell interference mitigation by coordinated transmission of the same information from multiple transmitting points. In this paper, we investigate the throughput and energy benefits of JT-CoMP transmission (over the conventional single-point transmission) in Long-Term Evolution (LTE) and LTE-Advanced homogeneous and heterogeneous network scenarios. For realistic rate/energy efficiency analysis, we propose a link-level modeling framework based on Finite State Markov Chain models for physical layer transport block transmission over the LTE radio access network. Results obtained show significant rate gains and energy savings using JT-CoMP (compared to the single-point transmission) especially for users in the cell-edge area. View full abstract»

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  • An improved inter-relay cooperation scheme for distributed relaying networks

    Page(s): 62 - 69
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (402 KB) |  | HTML iconHTML  

    We consider a two-hop distributed relaying network using orthogonal space-time block codes (OSTBC), where several relays using Decode-Forward (DF) support the transmission from one source to one destination. In order to mitigate the impact of error propagation for DF, an inter-relay cooperation (IRC) scheme allowing message exchanges among the relays was presented in our previous work based on punctured channel codes. Specifically, one of the relays that decodes the source message correctly re-generates and broadcasts the punctured bits as side information to support the relays with decoding errors for re-decoding. Subsequently, only the error-free relays transmit to the destination using OSTBC. It was shown that this IRC scheme may increase the number of error-free relays when at least one relay decodes the source message correctly. In this paper we focus on the scenario that all relays fail to decode the source message correctly. To this end, an improved IRC scheme is presented based on received signal exchange, in which the whole or part of the received frame are exchanged among the relays to apply signal combining. Additionally, the total energy consumption for signal transmission, baseband processing and RF circuit at all relays is evaluated for practical preferences. It is shown that the improved scheme outperforms our original scheme significantly with respect to the overall system throughput. View full abstract»

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  • A physical layer average consensus algorithm for wireless sensor networks

    Page(s): 70 - 77
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (506 KB) |  | HTML iconHTML  

    We propose a consensus algorithm for distributed average computation in a decentralized wireless network. In contrast to gossip-based schemes that operate on the network layer, our scheme is performed on the physical layer and exploits the broadcast character of the wireless channel. For the proposed scheme the sensor nodes in the network are partitioned into two groups of nodes. The nodes of each group transmit their information simultaneously in a given time slot while the nodes of the opposite group process the received superposition of signals. Each node's transmitted signal is constructed as a weighted sum of its received signals and its own data. The proposed scheme is energy efficient and associated with a moderate requirement in system overhead, e.g., associated with the acquisition of channel state information. Further, it offers fast convergence to the true mean of the sensor data in the network in a fully distributed manner. View full abstract»

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  • Interference cancellation and suppression in asynchronous cooperating base station systems

    Page(s): 78 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB) |  | HTML iconHTML  

    We consider cooperating base station systems where the users are not aligned in time and frequency to the core network as it is actually desired for coherent joint signal processing. As it is widely known, time and frequency offsets can cause inter-symbol as well as inter-carrier interference in OFDM systems which leads to a reduced transmission performance. In this paper we investigate uplink joint detection algorithms which, in addition to multi-user interference cancellation, reduce the asynchronous interference by using iterative interference cancellation as well as mitigating the additional interference by exploiting spatial diversity. The structure of the asynchronous interference in frequency domain can be exploited to derive algorithms with scalable complexity. As will be seen, particularly the interference suppression algorithm provides very good performance results with only a moderate complexity increase. View full abstract»

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  • Decentralized Q-learning of LTE-femtocells for interference reduction in heterogeneous networks using cooperation

    Page(s): 86 - 91
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (395 KB) |  | HTML iconHTML  

    Femtocells have become an attractive approach for operators to offer extended services on their licensed UMTS/LTE spectrum. They are typically deployed indoors to improve coverage and provide high data rates. As a drawback, femtocells may cause interference to other femtocells or to the macrocellular wireless network, especially in co-channel closed access deployment scenarios. In order to reduce this downlink interference, we propose a solution based on intelligent and self-organized femtocells implementing decentralized Q-learning algorithms. We introduce a criterion to measure the expertness of the femtocells in order to enable cooperation to those femtocells that are activated after a certain time. Newly activated and non-experienced femtocells measure the expertness of neighbour femtocells, assign a weight to their knowledge, and learn from them accordingly. System level simulation results demonstrate the effectiveness of the proposed approach. View full abstract»

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  • Parallel multiple candidate interference cancellation with distributed iterative multi-cell detection and base station cooperation

    Page(s): 92 - 96
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (254 KB) |  | HTML iconHTML  

    A novel cooperative interference mitigation strategy for an uplink cellular network with high frequency reuse factor is proposed in this paper. The cooperative base stations iteratively exchange their information among the neighbours while performing distributed signal processing. The base stations improve the estimate of the desired signal with each iteration and the exchanged information is used to regenerate the interference of the users from other cells. The interference is subsequently subtracted at the receiver resulting in an interference reduced signal. The exchange of soft information usually requires high communication bandwidth consumption of the network backhaul. In order to address this problem, we propose a strategy which exchanges only the hard information among the neighbours and a reliable hard interference cancellation procedure is introduced. The proposed algorithm is able to outperform the conventional soft cancellation based cooperation structure while requiring a reduced backhaul traffic. View full abstract»

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  • OFDM-IDM Space-Time Coding in two-hop relay-systems with error-prone relays

    Page(s): 97 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (441 KB) |  | HTML iconHTML  

    In this paper, the combination of distributed Interleave-Division-Multiplexing-Space-Time Codes (IDM-STCs) with Orthogonal Frequency Division Multiplexing (OFDM) in two-hop relay systems applying Decode-and-Forward (DF) is investigated. In order to cope with erroneous decoding at the relays, a model to capture the decoding reliabilities of the relays is formulated and a method to incorporate these reliabilities in the iterative detection process at the destination is presented. In addition, different approaches to keep the required signaling overhead low are discussed and compared with each other. It is shown, that the proposed scheme achieves significant gains over the common DF detection scheme assuming perfect decoding at the relays. Even with only one bit signaling per frame and relay an improvement of 3.6 dB can be obtained in certain scenarios. View full abstract»

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  • Energy-efficient device-to-device MIMO underlay network with interference constraints

    Page(s): 105 - 109
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (514 KB) |  | HTML iconHTML  

    Current interest is centered on non-orthogonal resource sharing between device-to-device (D2D) and cellular user equipments (C-UEs) that share the same frequency band, which then requires careful interference management techniques to avoid degrading the quality-of-service of the C-UEs. This work proposes an improved paradigm named device-to-multidevice (D2MD) communications, where a transmitting device communicates simultaneously with multiple receiving devices in an energy-efficient manner, and the underlay communication is augmented with the use of multiple transmit and receive antennas. Due to the difficulty of acquiring channel state information (CSI) of the C-UEs, we also present an enhanced D2MD scheme that does not require explicit feedback of CSI matrices from the C-UEs and/or D2MD receivers. Numerical simulations are presented to verify the efficacy of D2MD underlay transmission under a variety of CSI assumptions. View full abstract»

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  • 3D beamforming trials with an active antenna array

    Page(s): 110 - 114
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1661 KB) |  | HTML iconHTML  

    Beamforming techniques for mobile wireless communication systems like LTE using multiple antenna arrays for transmission and reception to increase the signal-to-noise-and-interference ratio (SINR) are state of the art. The increased SINR is not only due to a larger gain in the direction of the desired user, but also due to a better control of the spatial distribution of interference in the cell. To further enhance the system performance not only the horizontal, but also the vertical dimension can be exploited for beam pattern adaptation, thus giving an additional degree of freedom for interference avoidance among adjacent cells. This horizontal and vertical beam pattern adaptation is also referred to as 3D beamforming in the following. This paper describes investigations of the potential of 3D beamforming with lab and field trial setups and provides initial performance results. View full abstract»

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  • Max-min fair transmit beamforming for multi-group multicasting

    Page(s): 115 - 118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    In this paper, we consider transmit beamforming to multiple multicasting groups. We assume that the different multicasting groups share the same frequency band and that the channel state information (CSI) in terms of either instantaneous channels or the second order channel statistics is available at the transmitter. For the problem of maximizing the minimum signal-to-interference-plus-noise ratio (SINR) of all the receivers under a total power constraint, a sequential convex programming algorithm is developed. Compared to the method proposed in the literature, the developed algorithm achieves a higher SINR at a significantly reduced computational complexity. View full abstract»

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  • Linear precoding in MISO cognitive channels with degraded message sets

    Page(s): 119 - 124
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (339 KB) |  | HTML iconHTML  

    In this work, the coexistence of a single-input single-output (SISO) primary link and a multiple-input single-output (MISO) secondary link is considered, where the secondary transmitter has non-causal knowledge of primary message and transmits both primary and secondary messages. The optimal beamforming vectors and power allocation at the secondary transmitter are derived to maximize the achievable secondary rate while satisfying the primary rate requirement. Moreover, the optimal linear precoding is obtained by semidefinite relaxation and rank-one decomposition, when the number of antennas at the secondary transmitter is larger than two. Finally, the performance of the proposed scheme is evaluated through numerical simulations. View full abstract»

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  • On multiantenna sensor networks with interference: Energy consumption vs. robustness

    Page(s): 125 - 132
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (421 KB) |  | HTML iconHTML  

    In this paper, we consider power-controlled wireless multiantenna sensor networks with interference and study the general trade-off between energy consumption and quality-of-service expressed in terms of the signal-to-interference ratio (SIR). First, we develop a model for the energy consumption of multiantenna nodes (i.e., energy consumption for transmission and hardware) and then study the trade-off between accuracy and energy costs for channel estimation by deriving a bound for the estimation error variance, since most multiantenna strategies require adequate channel knowledge. Then, we numerically compare different MIMO strategies with the energy consumption and the achievable SIR of a standard SISO system, to obtain insights into the strength of the discussed trade-off and to provide guidelines on the choice of strategies for different applications. View full abstract»

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  • Handling unknown interference in cellular networks with interference coordination

    Page(s): 133 - 139
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (338 KB) |  | HTML iconHTML  

    We consider the downlink of a cellular network with cooperating multiple antenna base stations. On the one hand, each base stations tries to serve its associated mobile devices optimally, on the other hand, they try to minimize the interference they cause. Both goals could be achieved, if the interference channels would be zero. An adaptive beamforming based interference mitigation can only be performed for measured interference channels. To find an unachievable, but relatively tight upper bound we set the measured interference channels to zero. For such a limited cooperation, we show that the rates can be improved by predicting the interference over the unknown channels. View full abstract»

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  • Measurement of capacity enhancement with parasitic reconfigurable aperture antennas in interference-limited scenarios

    Page(s): 140 - 144
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (626 KB) |  | HTML iconHTML  

    The potential of capacity enhancement with a parasitic reconfigurable aperture (RECAP) antenna is investigated through a measurement campaign in line-of-sight (LOS) and non-LOS conditions in an indoor laboratory environment. Measurements are performed using a 5×5 parasitic RECAP for a bandwidth of 70 MHz centered at 2.55 GHz. Both noise-limited as well as interference-limited cases are considered with a varying level of interference under two different realistic power constraints: average receive signal-to-noise ratio (SNR) and fixed total transmit power. For RECAP optimization a simple genetic algorithm (GA) is implemented and its performance is compared with that of a random search. Measurements confirm that a large increase in capacity is possible especially for the case when there is high interference present. View full abstract»

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  • Performance comparison of distributed IDM-STC versus cooperative OFDM for practical decode-and-forward relay-networks

    Page(s): 145 - 151
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (381 KB) |  | HTML iconHTML  

    In this paper, we compare two different multiplexing strategies for a two-hop parallel relay channel. Precisely, we show the performance of distributed Interleave-Division-Multiplexing Space-Time Coding (dIDM-STC) and cooperative Orthogonal Frequency Division Multiplexing (cOFDM) operating in a decode-and-forward relay network, under the constraint of imperfect channel knowledge and timing and carrier frequency offsets. These impairments have to be estimated with either a complete pilot layer in dIDM-STC or orthogonal pilot symbols in cOFDM. While both schemes can cope with timing offsets of integer multiples of the sampling interval very well, cOFDM requires an adjustment of all transmit frequencies in order to avoid inter-carrier interference which would destroy orthogonality of the subcarriers and lead to severe performance degradations. View full abstract»

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