Dennis Goeckelhttps://works.bepress.com/dennis_goeckel/Recent works by Dennis Goeckelen-usCopyright (c) 2019 All rights reserved.Sun, 01 Feb 2009 00:00:00 +00003600Hybrid Coherent and Frequency-Shifted-Reference Ultrawideband Radiohttps://works.bepress.com/dennis_goeckel/3/Dennis GoeckelSun, 01 Feb 2009 00:00:00 +0000https://works.bepress.com/dennis_goeckel/3/ArticlesBounds on the Throughput Gain of Network Coding in Unicast and Multicast Wireless Networkshttps://works.bepress.com/dennis_goeckel/2/Gupta and Kumar established that the per node throughput of ad hoc networks with multi-pair unicast traffic scales with an increasing number of nodes n as λ(n) = Θ(1/√n log n), thus indicating that performance does not scale well. However, Gupta and Kumar did not consider network coding and wireless broadcasting, which recent works suggest have the potential to significantly improve throughput. Here, we establish bounds on the improvement provided by such techniques. For random networks of any dimension under either the protocol or physical model that were introduced by Gupta and Kumar, we show that network coding and broadcasting lead to at most a constant factor improvement in per node throughput. For the protocol model, we provide bounds on this factor. We also establish bounds on the throughput benefit of network coding and broadcasting for multiple source multicast in random networks. Finally, for an arbitrary network deployment, we show that the coding benefit ratio is at most O(log n) for both the protocol and physical communication models. These results give guidance on the application space of network coding, and, more generally, indicate the difficulty in improving the scaling behavior of wireless networks without modification of the physical layer.Dennis GoeckelThu, 01 Jan 2009 00:00:00 +0000https://works.bepress.com/dennis_goeckel/2/ArticlesAsymptotic Connectivity Properties of Cooperative Wireless Ad Hoc Networkshttps://works.bepress.com/dennis_goeckel/4/Extensive research has demonstrated the potential improvement in physical layer performance when multiple radios transmit concurrently in the same radio channel. We consider how such cooperation affects the requirements for full connectivity and percolation in large wireless ad hoc networks. Both noncoherent and coherent cooperative transmission are considered. For one-dimensional (1-D) extended networks, in contrast to noncooperative networks, for any path loss exponent less than or equal to one, full connectivity occurs under the noncoherent cooperation model with probability one for any node density. Conversely, there is no full connectivity with probability one when the path loss exponent exceeds one, and the network does not percolate for any node density if the path loss exponent exceeds two. In two-dimensional (2-D) extended networks with noncoherent cooperation, for any path loss exponent less than or equal to two, full connectivity is achieved for any node density. Conversely, there is no full connectivity when the path loss exponent exceeds two, but the cooperative network percolates for node densities above a threshold which is strictly less than that of the noncooperative network. A less conclusive set of results is presented for the coherent case. Hence, even relatively simple noncoherent cooperation improves the connectivity of large ad hoc networks.Dennis GoeckelThu, 01 Jan 2009 00:00:00 +0000https://works.bepress.com/dennis_goeckel/4/ArticlesA New Form of Network Coded Cooperative Transmission for Multiple Access Channelshttps://works.bepress.com/dennis_goeckel/35/Dennis GoeckelSat, 01 Nov 2008 00:00:00 +0000https://works.bepress.com/dennis_goeckel/35/Conference PublicationsReceiver Optimization in Frequency-Shifted Reference Ultra-Wideband (FSR-UWB) Systemshttps://works.bepress.com/dennis_goeckel/36/Dennis GoeckelWed, 01 Oct 2008 00:00:00 +0000https://works.bepress.com/dennis_goeckel/36/Conference PublicationsPerformance of UWB Systems in the Presence of Severe Multipath and Narrowband Interferencehttps://works.bepress.com/dennis_goeckel/38/Dennis GoeckelMon, 01 Sep 2008 00:00:00 +0000https://works.bepress.com/dennis_goeckel/38/Conference PublicationsThe Capacity of MIMO Systems with Increasing SNR by Electromagnetic Analysishttps://works.bepress.com/dennis_goeckel/5/The dependence of the communication capacity of multiple-input multiple-output (MIMO) wireless systems on the average received signal-to-noise ratio (SNR), assuming the channel is unknown at the transmitter and perfectly known at the receiver, is studied through full wave electromagnetic tools. Although it is commonly accepted that the capacity of a MIMO system increases linearly at high SNRs when plotted versus the SNR expressed in dB, the fact that the number of effective degrees of freedom (DOF) of the system increases with SNR in many practical environments calls this conclusion into question for reasonably high SNRs. Based on a full wave electromagnetic investigation, we are able to analytically predict and then confirm a significant region on the MIMO capacity curve where the capacity grows quadratically when plotted versus the SNR in dB. This gives analytical insight into a portion of the capacity curve that may previously be (incorrectly) attributed to the concavity of the logarithm function rather than the increase in electromagnetic degrees of freedom. The quadratic, rather than linear, growth of capacity suggests that it may be worthwhile to invest more transmit power to achieve higher performance gains. However, to fully take advantage of this second order benefit, the numbers of antennas at the transmitter and the receiver must be close to or slightly larger than the wavevector-aperture-product (WAP) of the corresponding EM system.Dennis GoeckelMon, 01 Sep 2008 00:00:00 +0000https://works.bepress.com/dennis_goeckel/5/ArticlesAntenna Beam Pattern Model for Cooperative Ad-Hoc Networkshttps://works.bepress.com/dennis_goeckel/37/Dennis GoeckelMon, 01 Sep 2008 00:00:00 +0000https://works.bepress.com/dennis_goeckel/37/Conference PublicationsA Relay Assisted Cooperative Transmission Protocol for Wireless Multiple Access Systemshttps://works.bepress.com/dennis_goeckel/6/In this paper, we propose a spectrally efficient cooperative transmission protocol for multiple access scenarios. The key feature is to utilize multi-user diversity and fully exploit the dynamic nature of radio propagation. In particular, by carefully scheduling the multiple sources and relays' transmissions, a source with a poor connection to the destination can have higher priority to obtain help from a relay with better channel condition. As a result, the full diversity gain is achievable even though only a fraction of relays is scheduled to help each user. We developed an achievable diversity-multiplexing tradeoff for the proposed transmission protocol to assist performance evaluation. When the number of relays is large, the diversity-multiplexing tradeoff achieved by the proposed scheme can approximate the optimal multiple-input single-output upper bound. Both analytical and numerical results show that the proposed protocol outperform other comparable schemes in most conditions.Dennis GoeckelFri, 01 Aug 2008 00:00:00 +0000https://works.bepress.com/dennis_goeckel/6/ArticlesThe Complex Envelope of a Bandlimited OFDM Signal Converges Weakly to a Gaussian Random Processhttps://works.bepress.com/dennis_goeckel/7/Orthogonal frequency division multiplexing (OFDM) systems have been used extensively in wireless communications in recent years; thus, there is significant interest in analyzing the properties of the transmitted signal in such systems. In particular, a large amount of work has focused on analyzing the variation of the complex envelope of the transmitted signal and on designing methods to minimize this variation. In this paper, it is established that the complex envelope of a bandlimited uncoded OFDM signal converges weakly to a Gaussian random process as the number of subcarriers goes to infinity. This shows that the properties of the OFDM signal will asymptotically approach those of a Gaussian random process over any finite time interval. The convergence proof is then extended to two important cases, namely, coded OFDM systems and systems with an unequal power allocation across subcarriers.Dennis GoeckelSun, 01 Jun 2008 00:00:00 +0000https://works.bepress.com/dennis_goeckel/7/Articles