We propose a concept system termed distributed base station (DBS), which enables distributed transmit beamforming at large carrier wavelengths to achieve significant range extension and or increased downlink data rate, providing a low-cost infrastructure for applications such as rural broadband. We consider a frequency division duplexed (FDD) system, using feedback from the receiver to achieve the required phase coherence. At a given range, @math cooperating transmitters can achieve @math -fold increase in received power compared to that for a single transmitters, and feedback-based algorithms with near-ideal performance have been prototyped. In this paper, however, we identify and address key technical issues in translating such power gains into range extension via a DBS. First, to combat the drop in per-node SNR with extended range, we design a feedback-based adaptation strategy that is suitably robust to noise. Second, to utilize available system bandwidth, we extend narrowband adaptation algorithms to wideband channels through interpolation over OFDM subcarriers. Third, we observe that the feedback channel may become a bottleneck unless sophisticated distributed reception strategies are employed, but show that acceptable performance can still be obtained with standard uplink reception if channel time variations are slow enough. We quantify system performance compactly via outage capacity analyses.
The present paper builds on our prior conference paper @cite_5 , which introduced the DOST scheme, and also discussed extensions to wideband systems. However, it goes well beyond @cite_5 by presenting a DBS concept system built around DOST, including an OFDM system design roughly consistent with LTE, specific prescriptions for pilot design, and outage capacity analyses for downlink and uplink which compactly characterize system-level performance.
@cite_5
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Orthogonal Frequency Division Multiplexing (OFDM) uses pilot tones to estimate the channel's frequency response and perform equalization. It is commonly known that jamming pilot tones is more efficient than broadband attacks against an entire OFDM signal. This paper builds on this idea and introduces the pilot nulling attack, which is considerably more efficient than simple pilot jamming, by driving received pilot energy as close to zero as possible. This paper presents our channel and equalizer model, and then undertakes an analysis of OFDM under these attacks, verifying the assessment through simulation. For a target bit error rate of 0.4, QPSK underlying modulation, and pilot tone density of 1 8, we discover that pilot jamming is roughly 2 dB more efficient than barrage jamming, and pilot nulling is roughly 7.5 dB more efficient than barrage jamming. In all cases, pilot nulling is capable of fully denying the target signal at 4 dB of signal-to-jamming ratio by driving the QPSK bit error rate to 0.5. Communication systems in practice are subject to many technical technological constraints and restrictions. Multiple input, multiple output (MIMO) processing in current wireless communications, as an example, mostly employs codebook-based pre-coding to save computational complexity at the transmitters and receivers. In such cases, closed form expressions for capacity or bit-error probability are often unattainable; effects of realistic signal processing algorithms on the performance of practical communication systems rather have to be studied in simulation environments. The Vienna LTE-A Uplink Simulator is a 3GPP LTE-A standard compliant MATLAB-based link level simulator that is publicly available under an academic use license, facilitating reproducible evaluations of signal processing algorithms and transceiver designs in wireless communications. This paper reviews research results that have been obtained by means of the Vienna LTE-A Uplink Simulator, highlights the effects of single-carrier frequency-division multiplexing (as the distinguishing feature to LTE-A downlink), extends known link adaptation concepts to uplink transmission, shows the implications of the uplink pilot pattern for gathering channel state information at the receiver and completes with possible future research directions. This paper presents a full duplex radio design using signal inversion and adaptive cancellation. Signal inversion uses a simple design based on a balanced unbalanced (Balun) transformer. This new design, unlike prior work, supports wideband and high power systems. In theory, this new design has no limitation on bandwidth or power. In practice, we find that the signal inversion technique alone can cancel at least 45dB across a 40MHz bandwidth. Further, combining signal inversion cancellation with cancellation in the digital domain can reduce self-interference by up to 73dB for a 10MHz OFDM signal. This paper also presents a full duplex medium access control (MAC) design and evaluates it using a testbed of 5 prototype full duplex nodes. Full duplex reduces packet losses due to hidden terminals by up to 88 . Full duplex also mitigates unfair channel allocation in AP-based networks, increasing fairness from 0.85 to 0.98 while improving downlink throughput by 110 and uplink throughput by 15 . These experimental results show that a re- design of the wireless network stack to exploit full duplex capability can result in significant improvements in network performance. As society continues to integrate information-based technologies into daily life, there is an increased need for small, powerful mobile phones. Recently, relaying technologies have been researched for standardization of the next generation of mobile communication systems, including third-Generation Partnership Project (3GPP) LTE-Advanced, IEEE 802.16j, and IEEE 802.16m. Especially, LTE-Advanced is an evolutionary version of IMT-2000 defined by the ITU. To satisfy these requirements, relaying technology is considered as a powerful candidate scheme with carrier aggregation, MIMO, and CoMP. Relaying technology has been introduced to guarantee high data rates to multiple users. It can also extend cell coverage or effectively increase the average throughput of the cell by installing relay nodes at cell edges or in shadow areas. Thus, in this paper, we propose a method for boosting reception performance using the downlink transmission method of the LTE system, which is the next-generation mobile communication technology standard currently underway in 3GPP. At the moment, orthogonal frequency division multiplexing (OFDM), which is suitable for high-speed data transmission and multipath, is commonly used in an LTE downlink system. However, the OFDM method has a disadvantage of displaying a relatively higher PAPR at the terminal since it basically uses a multi-carrier. To this end, single carrier division multiple access (SC-FDMA) is used in an LTE uplink system in order to compensate for this defect related to high PAPR of OFDM at such an important terminal where power efficiency is important. However, when the channels in the frequency domain deteriorate signals, SC-FDMA reveals a defect in that the impact of deteriorated parts spreads and causes performance degradation. To this end, we propose that a relay be installed between the station and terminal, the distance between BS and RS be set at 500 or 1,000 m, and orthogonal frequency division multiple access (OFDMA) and SC-FDMA be chosen as transmission methods of RS. This paper found SC-FDMA to be a better choice when RS is closer to BS, whereas OFDMA is a better choice when the distance between BS and RS is farther. The system's reception performance improved when the transmission method fit the circumstances in the middle between BS and MS. We study a multiple input multiple output (MIMO) cellular system where each base-station (BS) is equipped with a large antenna array and serves some single antenna mobile stations (MSs). With the same setup as in [1], the influence of orthogonal and non-orthogonal pilot sequences on the system performance is analytically characterized when each BS has infinitely many antennas. Using stochastic geometric modeling of the BS and MS locations, closed-form expressions are derived for the distribution of signal-to-interference-ratio (SIR) for both uplink and downlink. Moreover, they are shown to be equivalent for the orthogonal pilots case. Further, it is shown that the downlink SIR is greatly influenced by the correlations between the pilot sequences in the non-orthogonal pilots case. Finally, the mathematical tools can be used to study system performances with other general channel estimation methods and transmission-reception schemes. Orthogonal Frequency Division Multiplexing (OFDM) uses pilot tones to estimate and equalize the channel's frequency response whose locations and values are known. This makes OFDM prone to pilot tone based jamming attacks. Our previous research analyzed such jamming attacks. This paper builds on this idea and proposes approaches to mitigate the effect by randomizing pilot tone locations. It also presents OFDM channel and equalizer model, formulates channel estimation error, and then undertakes an analysis of OFDM system for randomized pilot tones, verifying through simulation. Both analytics and simulation show that randomized pilot tone schemes perform worse when a jammer is not present but perform better in the presence of pilot tone based jammer. Of the two proposed randomization schemes, the one that constrains the distance between random tones performs better in both scenarios. In this paper, the feasibility of user deployed femtocells in the same frequency band as an existing macrocell network is investigated. Key requirements for co-channel operation of femtocells such as auto-configuration and public access are discussed. A method for power control for pilot and data that ensures a constant femtocell radius in the downlink and a low pre-definable uplink performance impact to the macrocells is proposed, and the theoretical performance of randomly deployed femtocells in such a hierarchical cell structure is analysed for one example of a cellular UMTS network using system level simulations. The resulting impact on the existing macrocellular network is also investigated. Long-term evolution (LTE) is becoming the first choice of mobile network operators (MNOs) when constructing a wireless network infrastructure because of its high data rate, high throughput, and low latency. These significant advancements are necessary for satisfying the delivery of a wide-range of mobile applications and managed network resources. However, deploying a new LTE network or a transition from current legacy cellular networks to LTE can take several years to roll out. In the meantime, working in a heterogeneous wireless communication network looks inevitable. This paper investigates Voice over LTE (VoLTE) Quality of Service (QoS) under a heterogeneous wireless communication scenario. The contributions of this paper are twofold. First, a novel downlink (DL) semi-persistent scheduling scheme is proposed to reduce VoLTE end-to-end delay and increase system capacity. Second, an extensive network simulation model has been designed and implemented to evaluate the proposed scheme. The performance of the proposed scheme is compared with the performance of two relevant and well-known DL packet scheduling methods. The simulation results confirm that the proposed scheme is able to reduce VoLTE end-to-end delay and achieve a better system capacity than current methods, and maintain the desired VoLTE QoS. We study a distributed antenna system where L antenna terminals (ATs) are connected to a central processor (CP) via digital error-free links of finite capacity R0, and serve K user terminals (UTs). This model has been widely investigated both for the uplink (UTs to CP) and for the downlink (CP to UTs), which are instances of the general multiple-access relay and broadcast relay networks. We contribute to the subject in the following ways: 1) For the uplink, we consider the recently proposed “compute and forward” (CoF) approach and examine the corresponding system optimization at finite SNR. 2) For the downlink, we propose a novel precoding scheme nicknamed “reverse compute and forward” (RCoF). 3) In both cases, we present low-complexity versions of CoF and RCoF based on standard scalar quantization at the receivers, that lead to discrete-input discrete-output symmetric memoryless channel models for which near-optimal performance can be achieved by standard single-user linear coding. 4) We provide extensive numerical results and finite SNR comparison with other “state of the art” information theoretic techniques, in scenarios including fading and shadowing. The proposed uplink and downlink system optimization focuses specifically on the ATs and UTs selection problem. In both cases, for a given set of transmitters, the goal consists of selecting a subset of the receivers such that the corresponding system matrix has full rank and the sum rate is maximized. We present low-complexity ATs and UTs selection schemes and demonstrate through Monte Carlo simulation that the proposed schemes essentially eliminate the problem of rank deficiency of the system matrix and greatly mitigate the noninteger penalty affecting CoF RCoF at high SNR. Comparison with other state-of-the art information theoretic schemes, show competitive performance of the proposed approaches with significantly lower complexity. Dynamic downlink and uplink resource adaptation in TDD (Time Domain Duplex) systems by flexibly changing the ratio of time slots for downlink and uplink transmissions is studied under Heterogonous Network (HetNet) scenarios. The time-scale of the resource adaptation and the interference management between downlink and uplink transmissions from different cells are important factors in determining the achievable level of resource efficiency, user experience and energy saving in TDD systems. In this paper, we apply the dynamic downlink and uplink resource adaptation in multi-cell macro-pico scenarios with co-channel interference. The performance is evaluated in system level for LTE-Advanced TDD configurations. Reconfiguration rates of 10 msec and 640 msec are considered as the time-scale of the dynamic resource adaptation. In addition, the time domain inter-cell interference coordination between the macro cells and the pico cells is applied for handling the high level of interference from macro cells to pico cells in the downlink multi-cell dynamic simulations. This paper presents optimal and efficient suboptimal resource allocation algorithms for the downlink control channel of the Third Generation Partnership Project-Long Term Evolution (3GPP-LTE) standard. A novel formulation of this resource allocation problem as a pure binary-integer program called the set packing problem is performed. This problem has been well-studied in operations research. In addition a greedy heuristic sub-optimal algorithm that reduces the processing complexity involved in finding the optimal solution and also approaches the optimal performance is presented. Performance comparisons of these proposed schemes based on Monte-Carlo simulations in a 5 MHz bandwidth LTE system are provided. The results prove that the proposed algorithms can significantly improve the system's cell-edge performance. Scholars are increasingly citing electronic “web references” which are not preserved in libraries or full text archives. WebCite is a new standard for citing web references. To “webcite” a document involves archiving the cited Web page through www.webcitation.org and citing the WebCite permalink instead of (or in addition to) the unstable live Web page. This journal has amended its “instructions for authors” accordingly, asking authors to archive cited Web pages before submitting a manuscript. Almost 200 other journals are already using the system. We discuss the rationale for WebCite, its technology, and how scholars, editors, and publishers can benefit from the service. Citing scholars initiate an archiving process of all cited Web references, ideally before they submit a manuscript. Authors of online documents and websites which are expected to be cited by others can ensure that their work is permanently available by creating an archived copy using WebCite and providing the citation information including the WebCite link on their Web document(s). Editors should ask their authors to cache all cited Web addresses (Uniform Resource Locators, or URLs) “prospectively” before submitting their manuscripts to their journal. Editors and publishers should also instruct their copyeditors to cache cited Web material if the author has not done so already. Finally, WebCite can process publisher submitted “citing articles” (submitted for example as eXtensible Markup Language [XML] documents) to automatically archive all cited Web pages shortly before or on publication. Finally, WebCite can act as a focussed crawler, caching retrospectively references of already published articles. Copyright issues are addressed by honouring respective Internet standards (robot exclusion files, no-cache and no-archive tags). Long-term preservation is ensured by agreements with libraries and digital preservation organizations. The resulting WebCite Index may also have applications for research assessment exercises, being able to measure the impact of Web services and published Web documents through access and Web citation metrics. @PARASPLIT [J Med Internet Res 2005;7(5):e60] Recently, a lot of research effort has been spent on cross-layer system design. It has been shown that cross-layer mechanisms (i.e., policies) potentially provide significant performance gains for various systems. In this article we review several aspects of cross-layer system optimization regarding wireless OFDM systems. We discuss basic optimization models and present selected heuristic approaches realizing cross-layer policies by means of dynamic resource allocation. Two specific areas are treated separately: models and dynamic approaches for single transmitter receiver pairs (i.e., a point-to-point communication scenario) as well as models and approaches for point-to-multipoint communication scenarios (e.g., the downlink of a wireless cell). This article provides basic knowledge in order to investigate future OFDM cross-layer-optimization issues Full-duplex communication has the potential to substantially increase the throughput in wireless networks. However, the benefits of full-duplex are still not well understood. In this paper, we characterize the full-duplex rate gains in both single-channel and multi-channel use cases. For the single-channel case, we quantify the rate gain as a function of the remaining self-interference and SNR values. We also provide a sufficient condition under which the sum of uplink and downlink rates on a full-duplex channel is concave in the transmission power levels. Building on these results, we consider the multi-channel case. For that case, we introduce a new realistic model of a small form-factor (e.g., smartphone) full-duplex receiver and demonstrate its accuracy via measurements. We study the problem of jointly allocating power levels to different channels and selecting the frequency of maximum self-interference suppression, where the objective is maximizing the sum of the rates over uplink and downlink OFDM channels. We develop a polynomial time algorithm which is nearly optimal under very mild restrictions. To reduce the running time, we develop an efficient nearly-optimal algorithm under the high SINR approximation. Finally, we demonstrate via numerical evaluations the capacity gains in the different use cases and obtain insights into the impact of the remaining self-interference and wireless channel states on the performance. Future generation cellular networks are expected to provide ubiquitous broadband access to a continuously growing number of mobile users. In this context, LTE systems represent an important milestone towards the so called 4G cellular networks. A key feature of LTE is the adoption of advanced Radio Resource Management procedures in order to increase the system performance up to the Shannon limit. Packet scheduling mechanisms, in particular, play a fundamental role, because they are responsible for choosing, with fine time and frequency resolutions, how to distribute radio resources among different stations, taking into account channel condition and QoS requirements. This goal should be accomplished by providing, at the same time, an optimal trade-off between spectral efficiency and fairness. In this context, this paper provides an overview on the key issues that arise in the design of a resource allocation algorithm for LTE networks. It is intended for a wide range of readers as it covers the topic from basics to advanced aspects. The downlink channel under frequency division duplex configuration is considered as object of our study, but most of the considerations are valid for other configurations as well. Moreover, a survey on the most recent techniques is reported, including a classification of the different approaches presented in literature. Performance comparisons of the most well-known schemes, with particular focus on QoS provisioning capabilities, are also provided for complementing the described concepts. Thus, this survey would be useful for readers interested in learning the basic concepts before going into the details of a particular scheduling strategy, as well as for researchers aiming at deepening more specific aspects. With the recent advent of 4G LTE networks, there has been increasing interest to better understand the performance and power characteristics, compared with 3G WiFi networks. In this paper, we take one of the first steps in this direction. Using a publicly deployed tool we designed for Android called 4GTest attracting more than 3000 users within 2 months and extensive local experiments, we study the network performance of LTE networks and compare with other types of mobile networks. We observe LTE generally has significantly higher downlink and uplink throughput than 3G and even WiFi, with a median value of 13Mbps and 6Mbps, respectively. We develop the first empirically derived comprehensive power model of a commercial LTE network with less than 6 error rate and state transitions matching the specifications. Using a comprehensive data set consisting of 5-month traces of 20 smartphone users, we carefully investigate the energy usage in 3G, LTE, and WiFi networks and evaluate the impact of configuring LTE-related parameters. Despite several new power saving improvements, we find that LTE is as much as 23 times less power efficient compared with WiFi, and even less power efficient than 3G, based on the user traces and the long high power tail is found to be a key contributor. In addition, we perform case studies of several popular applications on Android in LTE and identify that the performance bottleneck for web-based applications lies less in the network, compared to our previous study in 3G [24]. Instead, the device's processing power, despite the significant improvement compared to our analysis two years ago, becomes more of a bottleneck. In this paper, turbo-based coding scheme for relay systems together with iterative decoding algorithms is designed. The performance of the proposed schemes is about 1.0-1.5 dB away from the information theoretical limits for various channel models. Coarse quantization at the base station (BS) of a massive multi-user (MU) multiple-input multiple-output (MIMO) wireless system promises significant power and cost savings. Coarse quantization also enables significant reductions of the raw analog-to-digital converter data that must be transferred from a spatially separated antenna array to the baseband processing unit. The theoretical limits as well as practical transceiver algorithms for such quantized MU-MIMO systems operating over frequency-flat, narrowband channels have been studied extensively. However, the practically relevant scenario where such communication systems operate over frequency-selective, wideband channels is less well understood. This paper investigates the uplink performance of a quantized massive MU-MIMO system that deploys orthogonal frequency-division multiplexing (OFDM) for wideband communication. We propose new algorithms for quantized maximum a posteriori channel estimation and data detection, and we study the associated performance quantization tradeoffs. Our results demonstrate that coarse quantization (e.g., four to six bits, depending on the ratio between the number of BS antennas and the number of users) in massive MU-MIMO-OFDM systems entails virtually no performance loss compared with the infinite-precision case at no additional cost in terms of baseband processing complexity. In this paper, we consider an adaptive modulation system with multiple-input-multiple-output (MIMO) antennas in conjunction with orthogonal frequency-division multiplexing (OFDM) operating over frequency-selective Rayleigh fading environments. In particular, we consider a type of beamforming with a maximum ratio transmission maximum ratio combining (MRT-MRC) transceiver structure. For this system, we derive a central limit theorem for various block-based performance metrics. This motivates an accurate Gaussian approximation to the system data rate and the number of outages per OFDM block. In addition to the data rate and outage distributions, we also consider the subcarrier signal-to-noise ratio (SNR) as a process in the frequency domain and compute level crossing rates (LCRs) and average fade bandwidths (AFBs). Hence, we provide fundamental but novel results for the MIMO OFDM channel. The accuracy of these results is verified by Monte Carlo simulations, and applications to performance analysis and system design are discussed. The LogicBlox system aims to reduce the complexity of software development for modern applications which enhance and automate decision-making and enable their users to evolve their capabilities via a self-service'' model. Our perspective in this area is informed by over twenty years of experience building dozens of mission-critical enterprise applications that are in use by hundreds of large enterprises across industries such as retail, telecommunications, banking, and government. We designed and built LogicBlox to be the system we wished we had when developing those applications. In this paper, we discuss the design considerations behind the LogicBlox system and give an overview of its implementation, highlighting innovative aspects. These include: LogiQL, a unified and declarative language based on Datalog; the use of purely functional data structures; novel join processing strategies; advanced incremental maintenance and live programming facilities; a novel concurrency control scheme; and built-in support for prescriptive and predictive analytics.