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ABSTRACT: This paper focuses on the Femtocell spectrum access problems when a certain amount of Femto Base Stations (FBS) are underlying in a two-tier cellular network, where the Macro Base Stations (MBS) are adopting Fractional Frequency Reuse (FFR) strategy. Under the first-tier outage constraints, the FBS transmission capacity in an analytic form has been presented. It is found via the relevant bound analysis that the optimal Femtocell spectrum access rate depends only on the basic configuration parameters of the Macrocell FFR, regardless the aspects of Femto transmit power and required QoS criteria. Consequently, the optimal Femtocell spectrum access algorithm is proposed in this paper, which achieves substantial gains over conventional algorithms. In the mean time, the maximal transmission capacity is not only related to the optimal access rate, but also to the system specific parameters such as Femto UE transmit power, target SIR and outage rate. Tuning these parameters enables the system to accommodate more number of FBSs simultaneously. Finally, the second-tier outage probability constraints are also derived, providing the optimal strategies for FBSs to maximize the second-tier throughput.
Communications Workshops (ICC), 2011 IEEE International Conference on; 07/2011
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ABSTRACT: In this paper, we investigate the impact of the transmit spatial correlation on the performance of the spatial multiplexing Multiple-Input Multiple-Output (MIMO) Multi-User (MU) Ultra-WideBand (UWB) system in which a pre-equalizer and a Time Reversal (TR) pre-filter are deployed at the transmitter. The combination of the pre-equalizer and the pre-filter is to mitigate the Multiple-Stream Interference (MSI) and Multiple-User Interference (MUI) caused by transmitting several independent data streams to different users simultaneously and the Inter-Symbol Interference (ISI) while the receivers are kept simple. In order to reduce the complexity of the transmitter, the selective-TR pre-filter is used.
Signal Processing and Communication Systems (ICSPCS), 2010 4th International Conference on; 01/2011
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9th International Symposium on Modeling and Optimization in Mobile, Ad-Hoc and Wireless Networks (WiOpt 2011), May 9-13, 2011, Princeton, NJ, USA; 01/2011
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ABSTRACT: To coexist with existing legacy wireless systems, the transmit power spectral density of ultrawideband (UWB) impulse radio systems is limited. The coverage range of UWB systems is then confined to within a few meters. Dual-hop relaying or multiple-input-multiple-output (MIMO) technology is one possible way of achieving greater UWB system coverage. This paper presents the design of dual-hop UWB MIMO relay systems (in which a source, relay, and destination have multiple antennas) according to the availability of channel state information (CSI) and their performance analysis over a UWB multipath fading channel. In particular, the decouple-and-forward and decode-and-forward relay systems are proposed when partial CSI is only available at the receiver side. On the other hand, with partial CSI being available at the transmitter side, we propose the amplify-and-forward and detect-and-forward relay systems. The exact formulas for the outage probabilities of those systems are derived. Furthermore, we evaluate, in closed form, the amount of fading and bit error rate expressions under sufficiently high signal-to-noise ratio and verify them through comparison with the simulation results. The effect of spatial correlation on the performance of our proposed systems is also studied. Numerical examples of the results provide valuable insights into the design of UWB MIMO relay systems.
IEEE Transactions on Vehicular Technology 08/2010; · 1.92 Impact Factor
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03/2010: pages 251 - 254; , ISBN: 9780470740019
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ABSTRACT: We introduce dual-hop ultra-wideband (UWB) relay systems using a multiple-antenna relay with antenna selection and the ones using single-antenna relay selection. In particular, amplify-and-forward (AF) and detect-and-forward (DTF) relaying schemes are considered for these systems. To study and compare the system performance, the exact formulae for the end-to-end signal-to-noise ratio (SNR) outage probabilities of the systems are derived. Numerical results show that the AF and DTF systems using the multiple-antenna relay with antenna selection outperform those using the single-antenna relay selection, respectively.
Source and Channel Coding (SCC), 2010 International ITG Conference on; 02/2010
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44th Annual Conference on Information Sciences and Systems, CISS 2010, Princeton, NJ, USA, 17-19 March 2010; 01/2010
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ABSTRACT: Orthogonal frequency division multiplexing (OFDM) signals are sensitive to the mismatching errors between the in-phase (I) and quadrature (Q) branches in the up and down-conversions. These mismatching errors including phase and amplitude mismatches make the signal constellation expand and rotate, which severely degrades the performance of OFDM systems. In this paper, a method of signal design for OFDM communication system is proposed in order to mitigate the impact of IQ mismatching errors. A simple quasi-symmetric conjugate (QSC) structure of signal in frequency domain designed at the transmitter side can completely remove the self-interference caused by IQ mismatching errors. At the receiver, the estimation and the compensation for IQ mismatch are not necessary. Analytic and simulation results can show the efficiency of QSC method in IQ mismatch mitigation compared to other techniques such as Adjacent Symbol Repetition (ASR), Adjacent Conjugate Symbol Repetition (ACSR), Symmetric Symbol Repetition (SSR), or Symmetric Conjugate Symbol Repetition (SCSR), respectively.
Personal, Indoor and Mobile Radio Communications, 2009 IEEE 20th International Symposium on; 10/2009
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ABSTRACT: A Multi-Input Multi-Output (MIMO) Ultra-Wide Band (UWB) communication system with Time Reversal (TR) is investigated in this paper. The system uses spatial multiplexing (SM) scheme to achieve high data rate. In order to cope with long delay spread of the UWB channel, time reversal technique is adopted at transmitter. Later a Multi Stream Interference (MSI) mitigation algorithm based on Zero Forcing (ZF) is proposed. The proposed ZF algorithm requires the knowledge of the channel state information (CSI), which is already available for time reversal at tranmitter. Simulation results show that the algorithm can considerably improve the BER performance of the system when the number of data streams is large (ges 3). This paper focuses on MIMO single user cases, however, the proposed MIMO-TR-UWB can be also extended to MIMO broadcasting system.
Ultra-Wideband, 2009. ICUWB 2009. IEEE International Conference on; 10/2009
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ABSTRACT: In this paper, we present detect-and-forward relaying approaches for a coherent ultra-wideband (UWB) detection (specifically selective-Rake reception) system and for a noncoherent UWB detection (specifically differential transmittedreference, DTR) system in order to achieve greater coverage in multipath fading channels. Multiple-antenna relay system are also proposed to further enhance the overall system performance. The corresponding bit error rate (BER) performance is evaluated theoretically and via simulations. The effect of some design factors on this performance is investigated. Analytical and simulation results verify the performance improvement of the proposed relay systems over the direct transmission systems.
IEEE Transactions on Wireless Communications 08/2009; · 2.59 Impact Factor
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ABSTRACT: An antenna selection scheme for multi-input multi-output (MIMO) ultra-wide band (UWB) communication system with time reversal (TR) is investigated in this paper. The system exploits spatial multiplexing (SM) scheme to achieve high data rate. In order to cope with long delay spread of the UWB channel, time reversal technique is adopted. TR can mitigate not only the interference intersymbol (ISI) but also multi stream interference (MSI) caused by transmitting several data streams simultaneously. Antenna selection algorithm allows to reduce the number of transmit antenna by using the channel state information (CSI), which is already available for time reversal. Simulation results show that the algorithm can considerably improve the BER performance of the system when the number of diversity branch is not so large.
Vehicular Technology Conference, 2009. VTC Spring 2009. IEEE 69th; 05/2009
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ABSTRACT: In order to coexist with existing legacy wireless systems, the transmit power spectral density (PSD) of ultra-wideband (UWB) impulse radio systems is limited. The coverage range of the UWB systems is then confined within a few meters. One possible way to achieve a greater coverage is a short-range multihop relaying strategy. This paper proposes a two-hop UWB relay system using multiple detect-and-forward relays, each of which is equipped with multiple antennas. Each multiple-antenna relay performs spatial diversity reception with partial-Rake scheme in the first hop, and decides whether or not to perform spatial transmit diversity with partial-pre-Rake scheme in the second hop. This leads not only to low complexity at the receiver, but also to reduced error propagation. Moreover, we derive the outage probability of the proposed relay system based on the IEEE 802.15.3a channel model. The effects of using multiple relay antennas, relays, and Rake/pre-Rake fingers on the outage performance are demonstrated. The tradeoffs among the numbers of relay antennas, relays, and Rake/pre-Rake fingers are also investigated. Numerical results show that it is best to use multiple relay antennas to improve the outage performance of the proposed system. Furthermore, in general, increasing the number of relays is more beneficial than increasing the number of Rake/pre-Rake fingers.
Vehicular Technology Conference, 2009. VTC Spring 2009. IEEE 69th; 05/2009
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04/2009: pages 65 - 72; , ISBN: 9780470740125
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ABSTRACT: In this paper, a dual-hop multiple-input multiple-output (MIMO) ultra-wideband (UWB) communication system in a frequency-selective fading environment is presented for the first time. The focus is on the case that partial channel state information (CSI) is only available at the receiver side. The relaying schemes associated with this case are proposed, and the exact outage probability analysis of the dual-hop MIMO UWB system using such relaying schemes is provided.
Information Sciences and Systems, 2009. CISS 2009. 43rd Annual Conference on; 04/2009
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ABSTRACT: Ultra-wide-band (UWB) technology combined with multiple transmit and receive antennas (MIMO) is a viable way to achieve data rates of more than 1 Gb/s for wireless communications. UWB is typically applied to short-range and therefore mainly indoor communications in environments characterized usually by dense multipath propagation. For this type of environment, MIMO systems allow for a substantial increase of spectral efficiency by exploiting the inherent array gain and spatial multiplexing gain of the systems. In this paper, we provide a brief overview for UWB-MIMO wireless technology. The overview covers channel capacity, space-time coding (STC), and beamforming. It is shown that the spectral efficiency is increased logarithmically and linearly , respectively, for single transmit and multiple receive antennas (SIMO) and MIMO systems. For multiple transmit and single receive antenna (MISO) systems, a threshold for the data transmission rate exists such that the spatial multiplexing gain can be obtained if the data rate is lower than this threshold, but it is not beneficial to deploy multiple transmit antennas if the required data rate is higher than the threshold. Two STC schemes for UWB-MIMO are briefly discussed, and their performance comparison is presented. A discussion about antenna selection is also presented, and the performance comparison between antenna selection and equal gain combiner is provided showing the diversity gain for some scenarios. For the beamforming, it is shown that the optimal beamformer is obtained if all the weighting filters in each antenna branch are identical. About the optimal beamformer, it is found that the amplitude of the side lobe is independent of the ray incidence angle, and the amplitude of the main lobe is increased by a fold of the element number in the array. Three kinds of beam patterns are defined, and the beamwidth of the main lobe is given. Experimental results based on an offline testbed are provided to verify so-
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me analytical results presented in this paper. Since UWB-MIMO is still in its research infancy, the aim of this paper is to present some first results on spatial multiplexing, STC, and beamforming to illustrate the potential of UWB-MIMO.
Proceedings of the IEEE 03/2009; · 6.81 Impact Factor
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Proceedings of the IEEE 20th International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2009, 13-16 September 2009, Tokyo, Japan; 01/2009
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IEEE Transactions on Wireless Communications. 01/2009; 8:3407-3414.
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IEEE Transactions on Signal Processing. 01/2009; 57:4196-4208.
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ABSTRACT: The mobile position estimation using time-of-arrival (ToA) is considered for the wireless NLoS geolocation exploring a signal strength(SS) based on path loss. As exploited the path attenuation, a hybrid SS-ToA approach indicates a performance improvement compared with the usual ToA method. To realize this prospect, it calls for an estimator to determine the mobile position from the time delay. In this paper, we show that the use of line-of-sight (LoS) time delay provides the same performance as that given by using both the LoS and non-LoS (NLoS) time delays. We then propose least squares (LS), weighted least squares (WLS) and maximum likelihood (ML) to estimate the mobile position. Theoretical performance of the LS and WLS is analyzed. It reveals that for different LoS time delay error variances, the LS error variance is larger than the WLS error variance, which is equal to the Cramer-Rao bound (CRB). Numerical results illustrate that the time delay performance analysis is accurate when the time delay estimate is close to its true value, i.e. for small time delay error variance. For high SNR and large effective bandwidth, the LS cannot provide the performance compared with the CRB, whereas the WLS and ML are statistically efficient.
Wireless Communications and Networking Conference, 2009. WCNC 2009. IEEE; 01/2009
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ABSTRACT: This paper discusses the channel capacity of multiantenna ultra-wideband (UWB) indoor wireless systems. It is shown first that for both single-input single-output (SISO) and multiple-input multiple-output (MIMO) cases, when the transmit SNR is lower than some value, say -20 dB, using optimal power spectrum allocation (OPSA) at the transmitter side can increase the reliable transmission rate considerably compared to the uniform power spectrum allocation scheme, while when the transmit signal-to-noise ratio (SNR) is higher than some value, say 10 dB, the benefit of OPSA is very limited. Therefore, measures such as the water-filling algorithm should be taken to make full use of the frequency-selectivity of UWB systems if the transmit SNR is low. Second, in the multiple-input single-output (MISO) case, the outage probability decreases with the number of transmit antennas when the communication rate is lower than some value, but increases instead when the rate is higher than another value. A critical transmission rate is identified. Third, in the cases of SIMO and MIMO, the communication rate supportable by the channel with a given outage probability increases approximately logarithmically and linearly , respectively, with the number of receive antennas.
IEEE Transactions on Signal Processing 01/2009; · 2.63 Impact Factor
