1,720,978 research outputs found
A simple multi-antenna transceiver for ultra wide band based 4GWLANs
No full textIn the last years a lot of attention has been paid to multi-antenna systems with Space-Time Coding (STC) and to Ultra Wide Band (UWB). In this paper we aim to propose a transceiver scheme in order to evaluate if these two technologies can be considered adequate candidates for next generation WLANs. Merging Ultra Wide Band signals with Multiple Antenna schemes allows us to achieve very high bit rate and error probability matched to QoS requested by 4GWLANs at low SNR. This contribution presents a simple way to combine Ultra Wide Band and Multiple Antenna schemes so to improve performance and coverage with respect to the conventional UWB approach in order to promote this approach application scenarios by considering a base band channel model and selective are considered
On the information throughput and optimized power allocation for MIMO wireless systems with imperfect channel estimation
No full textIn this paper, we focus on the throughput analysis, outage evaluation and optimized power allocation for Multiple-Input Multiple-Output (MIMO) pilot-based wireless systems subject to short-term constraints on the radiated power and equipped with a feedback-path for communicating back to the transmitter the imperfect MIMO channel estimates available at the receiver. The case of the ergodic throughput for Gaussian distributed input signals is analyzed, and the conditions for the (asymptotical) achievement of the Shannon capacity are pointed out. The main contributions of this work may be so summarized. First, we develop closed-form analytical expressions for the computation of the ergodic information throughput conveyed by the considered MIMO system for the case of ideal feedback link. Second, we present an iterative algorithm for the optimized power allocation over the transmit antennas that explicitly accounts for the imperfect MIMO channel estimates available at the receiver. Third, after relaxing the assumption of ideal feedback link, we test the sensitivity of the proposed power allocation algorithm on errors possibly introduced by the feedback channel, and then, we numerically evaluate the resulting throughput loss. Finally, we develop closed-form upper and lower bounds on the outage probability that are asymptotically tight
Performance analysis of impulse-radio UWB networks impaired by multiple access interference
No full textIn this contribution we analyse the effect of Multi-User Interference in terms of user collision probability and collision probability at all, by showing the impact that different system parameters have on the collision probability and the effect that this last presents on codeword error probability both in Forward Error Correcting (FEC) and Automatic Repeat reQuest (ARQ) schemes. © 2005 IEEE
A novel multi-antenna impulse radio UWB transceiver for broadband high-throughput 4G WLANs
No full textIn the last years, a lot of attention has been devoted to both multi-antenna systems with space-time orthogonal block coding (STOBC) and ultra wideband (UWB) transceivers based. on impulse-radio (IR) technologies. In this short contribution we anticipate the architecture of a novel transceiver merging both multi-antenna and pulse position modulation (PPM) IR-UWB techniques and then we test the performance in flat-faded application scenarios typical of emerging broadband 4G WLANs. Three main appealing features are retained by the sketched transceiver scheme. First, it allows to equip the UWB receiver with reliable estimates of the (possibly time-varying) underlying multiple-input multiple-output (MIMO) UWB without reducing the overall information throughput conveyed by the system. Second, the performance confirms that the proposed transceiver is able to achieve "full diversity" even at SNRs as low as 1.5-2 dB. As a consequence, the resulting BERs outperform those of current Single-Input Single-Output (SISO) IR-UWB transceivers over two orders of magnitude even at SNR's as low as 3-4 dB. Third, at target BER's below 10(-2) and radiated powers around 250 muW, the coverage ranges allowed by the proposed MIMO IR-UWB scheme typically outperform those of conventional SISO IR-UWB ones of about two orders of magnitude
Contracted QoS policies for distributed space division multiple access for "ad-hoc" networks
No full textThis paper focuses on the competitively optimal power-control and signal-shaping for "ad-hoc" networks composed by Multiple-Antenna noncooperative transmit/receive terminals affected by spatially colored Multiple-Access Interference (MAI). For this purpose, the MAI-impaired network is modeled as a noncooperative strategic game, and sufficient conditions for the existence and uniqueness of the Nash Equilibrium are provided. Connection Admission Procedures are presented with related performance
Multipath-Resistant Incoherent Space-Time Codes for IR-UWB MIMO Systems2007 IEEE International Conference on Communications
No full textIn this contribution we develop a Multiple-Input Multiple-Output (MIMO) Impulse Radio Ultra Wide Band (IR-UWB) transceiver for Orthogonal signalling over (baseband) multipath faded MIMO channels. The proposed Maximum-Likelihood receiver results to be "partially coherent", since it is optimized to work without any information about channel coefficients, and it is based on the knowledge of the arrivals' times of the transmitted signals' replicas. The behavior of the proposed transceiver has been evaluated via three suitable versions of the Union-Chernoff Bound related to several indoor and outdoor propagation scenarios, and these limits are considered to introduce a novel family of unitary orthogonal Space-time Block Codes (e.g., the Space-Time OPPM (STOPPM) codes), that are able to attain maximum diversity and coding gains. © 2007 IEEE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Interference suppression in MIMO systems for throughput enhancement and error reduction
No full textThis contribution analyzes the problem of multi-user interference suppression via estimation and subtraction. In particular it is shown that spatial diversity helps the suppression capability of a Base Station and this has an important impact on performance. By fact, we show that the best solution does not consist in transmit at maximum energy level but, in order to allow interference estimation and cancellation, a trade off has to be solved. So, interference suppression can give arise to performance improvements both for achieved throughput (that can be "enhanced") and for error probability (that can be reduced). Copyright 2006 ACM
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