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Communications, IEEE Transactions on

Issue 10 • Date Oct. 2004

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Displaying Results 1 - 25 of 34
  • Table of contents

    Publication Year: 2004 , Page(s): c1 - c4
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  • IEEE Transactions on Communications publication information

    Publication Year: 2004 , Page(s): c2
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  • Blind symbol-timing and frequency-offset estimation in OFDM systems with real data symbols

    Publication Year: 2004 , Page(s): 1609 - 1612
    Cited by:  Papers (24)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    In this letter, the problem of blind symbol-timing and frequency-offset estimation in orthogonal frequency-division multiplexing (OFDM) systems with real data symbols is considered. Maximum-likelihood (ML) estimators for the parameters of interest have been derived by modeling the OFDM signal as a proper complex Gaussian random process. However, when data symbols belong to a real constellation, the received signal becomes an improper complex random process, and hence, previously mentioned estimators, termed cyclic prefix (CP) estimators, are not ML estimators. In this letter, minimum mean-squared error estimators exploiting the conjugate-symmetry property exhibited by the OFDM signal with real data symbols, termed MSR estimators, that greatly outperform CP estimators in additive noise channels, are derived. Moreover, a modified MSR symbol-timing estimator that can assure satisfactory performance in multipath fading channels is proposed. View full abstract»

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  • On decision-feedback detection of differential space-time modulation in continuous fading

    Publication Year: 2004 , Page(s): 1613 - 1617
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    We show that linear prediction (LP)-based decision-feedback detection (DFD) for nondiagonal differential space-time modulation (DSTM) may suffer from a severe performance degradation in continuously fading channels. DSTM constellations that incur no degradation in LP-DFD are identified as those with a diagonal generator. To cater to other constellations, we propose a low-complexity DFD scheme by inserting decision-feedback symbols into the metric of multiple-symbol differential detection. View full abstract»

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  • An upper bound on the average throughput of opportunistic transmission in a multiple-access fading channel

    Publication Year: 2004 , Page(s): 1618 - 1621
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    This letter considers a multiple-access fading channel with opportunistic transmission of the users, i.e., only the user with the highest received power is allowed to transmit at a certain time slot. The transmit power randomization, independent of the channel estimates, is used in order to increase the fading rate, decrease the latency, and shape the distribution of the received powers. We derive the optimal distribution of the received powers that maximizes the throughput of the system, and measure possible gains compared with the long-term average throughput of the opportunistic transmission in a Rayleigh fading channel. The issue of unequal fading distributions of different users is also addressed. View full abstract»

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  • Analysis of diffuse optical wireless channels employing spot-diffusing techniques, diversity receivers, and combining schemes

    Publication Year: 2004 , Page(s): 1622 - 1631
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (984 KB) |  | HTML iconHTML  

    In this letter, the performance of an indoor optical wireless spot-diffusing system using various multibeam transmitter configurations, in association with direction diversity and combining techniques, is assessed and compared under the impact of multipath dispersion and ambient light noise through theoretical analysis and computer simulation. Computer simulation for three different multibeam transmitter configurations and a conventional diffuse transmitter is carried out. Diversity receiver and wide field-of-view (FOV) receiver configurations are evaluated in conjunction with the proposed configurations. For the diversity-detection case, a receiver comprising an array of narrow FOV detectors (three and seven segments) oriented in different directions is used to maximize the collected signals and minimize noise. A novel line-strip multibeam system (LSMS) is investigated with single and diversity receiver configurations, and is compared with other spot-diffusing methods. Combining schemes, including selection combining, maximum ratio combining, and equal gain combining are employed for the presented configurations. Our results indicate that the performance improvement obtained through the use of LSMS with a three-direction diversity receiver is about 20 dB signal-to-noise ratio enhancement over the conventional diffuse system, and 26 dB when combining techniques are used. Root mean square delay-spread performance for the proposed configurations, at different positions on the communication floor, are also evaluated and compared. View full abstract»

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  • Adaptive-modulation schemes for minimum outage probability in wireless systems

    Publication Year: 2004 , Page(s): 1632 - 1635
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    Adaptive-modulation schemes are designed that yield the minimum outage probability for wireless systems with strict delay constraints, under the assumption of perfect causal channel state information at the transmitter and receiver. Numerical results indicate that the proposed schemes significantly outperform adaptive schemes designed to maximize the average rate. View full abstract»

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  • Some results on the self-similarity property in communication networks

    Publication Year: 2004 , Page(s): 1636 - 1642
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    Due to the strong experimental evidence that packet network traffic is self-similar in nature, it is important to study the problems to see whether the superposition of self-similar processes retains the property of self-similarity, and whether the service of a server changes the self-similarity property of the input traffic. In this letter, we first discuss some definitions and superposition properties of self-similar processes. We obtain some good results about the property of merging self-similar data streams. Then we present a model of a single server with infinite buffer and prove that when the queue length has finite second-order moment, the input process, being strong asymptotically second-order self-similar (sas-s), is equivalent to the output process which also bears the sas-s property. View full abstract»

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  • A modified Gardner detector for symbol timing recovery of M-PSK signals

    Publication Year: 2004 , Page(s): 1643 - 1647
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    In this letter, we propose a modified version of the Gardner detector for symbol timing recovery of M-ary phase-shift keying (M-PSK) signals. Simulation results show that the proposed modification leads to significant performance improvement when M-PSK signals are highly bandlimited and M is small. Specifically, the reduction in the level of self-noise due to the modification amounts to 10.7 dB for quaternary phase-shift keying signals with the rolloff factor of 0.25 and the normalized noise-equivalent loop bandwidth of 0.005. In terms of computational complexity involved, the proposed method has an advantage over the known self-noise reduction methods for M-PSK signals with small M. View full abstract»

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  • Transmit diversity for combined 2G and 3G CDMA systems

    Publication Year: 2004 , Page(s): 1648 - 1653
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    In this letter, we propose modifications to existing transmit-diversity techniques to provide transmit diversity in code-division multiple-access cellular systems which must support both second-generation and third-generation mobiles on a common carrier. The proposed method, which we call symmetric-sweep transmit diversity, combines phase-sweep transmit diversity (PSTD) and space-time spreading (STS) in a way that allows second-generation and non-STS-capable mobiles to obtain the full advantage of PSTD, while third-generation mobiles obtain the full advantage of STS. View full abstract»

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  • On the ergodic capacity as a function of the correlation properties in systems with multiple transmit antennas without CSI at the transmitter

    Publication Year: 2004 , Page(s): 1654 - 1657
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB) |  | HTML iconHTML  

    In this letter, the impact of correlation of the transmit antennas of a multiple-input single-output (MISO) system, with no channel state information (CSI) at the transmitter and perfect CSI at the receiver is analyzed. We show that the ergodic capacity for the single-user MISO system is Schur-concave with respect to the vector with eigenvalues of the channel covariance matrix, i.e., the more correlation that exists between the transmit antennas, the less is the achievable capacity. Furthermore, the capacity loss for fully correlated transmit antennas in comparison with the uncorrelated case is derived. The results for the ergodic capacity are compared with the impact of correlation on the outage probability. The relationship between correlation properties and outage probability is more complicated than the relationship between the correlation properties and the ergodic capacity. It is shown that the outage probability is Schur-convex in the high signal-to-noise ratio (SNR) regime, and Schur-concave in the low SNR regime. View full abstract»

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  • Transmit power allocation for BER performance improvement in multicarrier systems

    Publication Year: 2004 , Page(s): 1658 - 1663
    Cited by:  Papers (38)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB) |  | HTML iconHTML  

    In a multicarrier system, transmit power allocation over different subchannels is an effective means of improving the performance. We develop the optimal transmit power allocation scheme to improve bit-error rate (BER) performance in a multicarrier system with diversity reception. A simple suboptimal scheme is also derived from the optimal one, and an asymptotic case referred to as the equal-signal-to-noise ratio scheme is discussed. Numerical results show that the optimal and suboptimal power allocation schemes significantly outperform the equal power allocation scheme. The effects of the modulation level, the number of receiving antennas, and the number of subchannels on the BER performance are also investigated. View full abstract»

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  • Multicarrier CDMA overlay for ultra-wideband communications

    Publication Year: 2004 , Page(s): 1664 - 1669
    Cited by:  Papers (47)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    In this letter, the performance of multicarrier code-division multiple-access (CDMA) systems is studied in the presence of narrowband interference for future ultra-wideband (UWB) communications. A Nakagami fading channel is assumed, and notch filters along with diversity techniques are used in the multicarrier CDMA receiver. A complete performance analysis of error probability is given. It is shown that when the number of subcarriers jammed by narrowband interference is small, the multicarrier receiver without notch filters can work well, due to the gain of frequency diversity from nonjammed subcarriers. On the other hand, when the number of subcarriers jammed by the narrowband interference is large, using notch filters can improve the multicarrier system performance significantly. View full abstract»

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  • On the design of adaptive space-time codes

    Publication Year: 2004 , Page(s): 1670 - 1674
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    In this letter, we investigate the design of adaptive space-time codes that exploit partial transmitter channel state information (CSI). We introduce the adaptive space-time parsing paradigm as a generalization of the transmitter selection-diversity approach. We then use this new framework to construct full-diversity adaptive space-time codes for delay-limited applications with fixed-rate transmission. The proposed codes allow for reduced-complexity decoders and are robust to inaccuracies in the transmitter CSI. View full abstract»

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  • Application layer error-correction coding for rate-distortion optimized streaming to wireless clients

    Publication Year: 2004 , Page(s): 1675 - 1687
    Cited by:  Papers (17)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB) |  | HTML iconHTML  

    This paper addresses the problem of streaming packetized media over a lossy packet network to a wireless client, in a rate-distortion optimized way. We introduce an incremental redundancy error-correction scheme that combats the effects of both packet loss and bit errors in an end-to-end fashion, without support from the underlying network or from an intermediate base station. The scheme is employed within an optimization framework that enables the sender to compute which packets it should send, out of all the packets it could send at a given transmission opportunity, in order to meet an average transmission-rate constraint while minimizing the average end-to-end distortion. Experimental results show that our system is robust and maintains quality of service over a wide range of channel conditions. Up to 8 dB performance gains are registered over systems that are not rate-distortion optimized, at bit-error rates as large as 10-2. View full abstract»

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  • On performance bounds for space-time codes on fading channels

    Publication Year: 2004 , Page(s): 1688 - 1697
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    We evaluate truncated union bounds on the frame-error rate (FER) performance of space-time (ST) codes operating over the quasi-static fading channel and compare them with computer simulation results. We consider both ST trellis and block codes. We make the following contributions. For the case of ST trellis codes, we develop a general method, which we denote as measure spectrum analysis, that characterizes ST codeword differences and accommodates the combined influences of the ST code and channel scenario. We propose a numerical bounding method that converges in the measure spectrum to within a very small fraction of a decibel to the simulated FER over the full range of signal-to-noise ratio. In addition, we demonstrate the existence of dominant quasi-static fading error events and detail a method for predicting them. Using only this set of dominant measure spectrum elements, very rapid and tight numerical estimation of FER performance is attained. View full abstract»

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  • Achievable information rates and coding for MIMO systems over ISI channels and frequency-selective fading channels

    Publication Year: 2004 , Page(s): 1698 - 1710
    Cited by:  Papers (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    We propose a simulation-based method to compute the achievable information rates for general multiple-input multiple-output (MIMO) intersymbol interference (ISI) channels with inputs chosen from a finite alphabet. This method is applicable to both deterministic and stochastic channels. As an example of the stochastic MIMO ISI channels, we consider the multiantenna systems over frequency-selective fading channels, and quantify the improvement in the achievable information rates provided by the additional frequency diversity (for both ergodic and nonergodic cases). In addition, we consider the multiaccess multiantenna system and present some results on the achievable information-rate region. As for the deterministic MIMO ISI channels, we use the binary-input multitrack magnetic recording system as an example, which employs multiple write and read heads for data storage. Our results show that the multitrack recording channels have significant advantages over the single-track channels, in terms of the achievable information rates when the intertrack interference is considered. We further consider practical coding schemes over both stochastic and deterministic MIMO ISI channels, and compare their performance with the information-theoretical limits. Specifically, we demonstrate that the performance of the turbo coding/decoding scheme is only about 1.0 dB away from the information-theoretical limits at a bit-error rate of 10-5 for large interleaver lengths. View full abstract»

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  • Generalized switch-and-examine combining (GSEC): a low-complexity combining scheme for diversity-rich environments

    Publication Year: 2004 , Page(s): 1711 - 1721
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    In diversity-rich environments, there is a tradeoff between performance and complexity. While combining a large number of diversity paths improves the system performance, it also increases the receiver complexity. With this in mind, we propose generalized switch and examine combining (GSEC) as a good candidate combining scheme for such environments. Description of the GSEC mode of operation shows that this scheme conserves a fixed complexity as the number of diversity paths increases, and offers a considerable complexity savings over traditional maximum ratio combining and even other low-complexity schemes, such as generalized selection combining. In this paper, we look into the design and performance analysis of GSEC over independent and identically distributed diversity paths. As an illustration of the mathematical formalism, selected numerical examples are provided, together with some related discussions and interpretations. View full abstract»

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  • Adaptive joint detection of cochannel signals for TDMA handsets

    Publication Year: 2004 , Page(s): 1722 - 1732
    Cited by:  Papers (5)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    In mobile communication systems, downlink (forward link) system capacity is limited by the ability of mobile receivers to recover the desired signal in the presence of cochannel interference (CCI). Joint detection of the desired and cochannel signals is a useful approach to improving receiver performance, thus increasing system capacity. In this paper, we show that a practical single-antenna joint-detection receiver can provide significant gains in system capacity for the time-division multiple-access (TDMA) standard Telecommunications Industry Association/Electronic Industry Association/Interim Standard-136 (TIA/EIA/IS-136 or IS-136). For a sectorized system, joint detection provides a capacity gain of 47% in a typical urban environment. When used in conjunction with transmit beamforming, the synergy between the two approaches leads to a capacity gain of over 200%. In determining these gains, practical aspects of the IS-136 system are considered, namely, unsynchronized networks, limited receiver complexity, and adaptability. A semiblind acquisition process, which uses the training sequence of the desired user only, is employed, because the desired and interfering base stations are not synchronized. The receiver complexity is controlled by processing only one sample per symbol period, even though it is shown that multiple samples per symbol period should ideally be used. Finally, because receiver performance may be limited by its own intersymbol interference instead of CCI, an adaptive joint-detection process is used which selects between joint demodulation and single-user equalization for each slot. View full abstract»

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  • Envelope-aided Viterbi receivers for GMSK signals with limiter-discriminator detection

    Publication Year: 2004 , Page(s): 1733 - 1746
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (872 KB) |  | HTML iconHTML  

    Continuous phase modulation schemes, such as Gaussian minimum-shift keying (GMSK), are frequently used with limiter-discriminator (LD) detectors. This paper studies how the side information derived from the signal envelope can enhance the performance of a Viterbi algorithm (VA)-based receiver operating on the LD output of a GMSK scheme. By considering the joint probability density function of envelope and frequency, different approximations yield different novel metrics for VA, using the three-variables envelope and its derivative, and frequency error in different combinations. Simulation results confirm that such envelope-aided VA gives significant performance gains, and that envelope information complements the frequency information output by the LD detector in frequency-selective fading channels. View full abstract»

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  • Multicast traffic scheduling in single-hop WDM networks with arbitrary tuning latencies

    Publication Year: 2004 , Page(s): 1747 - 1757
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (736 KB) |  | HTML iconHTML  

    To accommodate the demands of quality of service (QoS) and multicast applications, a multicast QoS traffic-scheduling algorithm with tuning latency consideration in wavelength-division multiplexing star-coupled networks is provided in this paper. To furnish different levels of QoS, two classes of traffic are considered: constant bit rate and available bit rate (ABR). An effective bandwidth-normalization scheme for ABR traffic is also derived. We define the slot scanning problem in the connection-setup process as the maximum assignable slots (MAS) problem. We prove that the optimal solution of the MAS problem can be obtained in polynomial time. Owing to its high-order time complexity, we also propose two heuristics for the MAS problem. The performance of these strategies are evaluated and compared by simulations under different system parameters, such as number of wavelengths, traffic load, and tuning latency. View full abstract»

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  • Accurate evaluation of multiple-access performance in TH-PPM and TH-BPSK UWB systems

    Publication Year: 2004 , Page(s): 1758 - 1766
    Cited by:  Papers (97)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB) |  | HTML iconHTML  

    A characteristic function method is proposed for precisely calculating the bit-error probability of time-hopping (TH) ultra-wideband (UWB) systems with multiple-access interference in an additive white Gaussian noise environment. The analytical expressions are validated by simulation and used to assess the accuracy of the Gaussian approximation. The Gaussian approximation is shown to be inaccurate for predicting bit-error rates (BERs) for medium and large signal-to-noise ratio (SNR) values. The performances of TH pulse position modulation (PPM) and binary phase-shift keying (BPSK) modulation schemes are accurately compared in terms of the BER. It is shown that the BPSK system outperforms the binary PPM system for all values of SNR. The sensitivity of the performance of the modulation schemes to the system parameters is also addressed through numerical examples. View full abstract»

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  • A novel channel-identification method for wireless communication systems

    Publication Year: 2004 , Page(s): 1767 - 1776
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB) |  | HTML iconHTML  

    We present a novel dual-channel identification approach for mobile wireless communication systems. Unlike traditional channel-estimation methods that rely on training symbols, we propose a bent-pipe feedback mechanism which requires the mobile station (MS) to send portions of its received signal back to the base station (BS) for wireless channel identification. Using a filter-bank decomposition concept, we introduce an effective algorithm that can identify both the forward and the reverse channels based only on this feedback information. This new method permits transfer of computational burden from the MS to the resource-rich BS, and leads to significant savings in bandwidth-consuming training signals. View full abstract»

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  • Power control, capacity, and duality of uplink and downlink in cellular CDMA systems

    Publication Year: 2004 , Page(s): 1777 - 1785
    Cited by:  Papers (44)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB) |  | HTML iconHTML  

    Accurate power control is an essential requirement in the design of cellular code-division multiple-access (CDMA) systems. In this paper, we contribute three main themes to the power control problem. First, we derive an efficient algorithm for computing minimal power levels for large-scale networks within seconds. Nice and intuitive conditions for the existence of feasible power solutions follow from this approach. Second, we define the capacity region of a network by the set of effective spreading gains, or data rates, respectively, which can be supplied by the network. This is achieved by bounding the spectral radius of a certain matrix containing system parameters and mutual transmission gain information. It is shown that the capacity region is a convex set. Finally, we reveal an interesting duality between the uplink and downlink capacity region. In a clear-cut analytical way, it substantiates the fact that the uplink is the more restricting factor in cellular radio networks. The same methods carry over to certain models of soft handover. In the case that the channel gains are subject to log-normal shadowing, we introduce the concept of level-α capacity regions. Despite the complicated structure, it can still be shown that this set is sandwiched by two convex sets coming arbitrarily close as variance decreases. View full abstract»

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  • Measurement and modeling of an ultra-wide bandwidth indoor channel

    Publication Year: 2004 , Page(s): 1786 - 1796
    Cited by:  Papers (135)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (968 KB) |  | HTML iconHTML  

    This paper describes the results of frequency-domain channel sounding in residential environments. It consists of detailed characterization of complex frequency responses of ultra-wideband (UWB) signals having a nominal center frequency of 5 GHz. A path loss model as well as a second-order autoregressive model is proposed for frequency response generation of the UWB indoor channel. Probability distributions of the model parameters for different locations are presented. Also, time-domain results such as root mean square delay spread and percent of captured power are presented. View full abstract»

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Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

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Editor-in-Chief
Robert Schober
University of British Columbia