Youngho Jo

Bio: Youngho Jo is an academic researcher from University of Florida. The author has contributed to research in topics: Bit error rate & Spread spectrum. The author has an hindex of 3, co-authored 5 publications receiving 12 citations. Previous affiliations of Youngho Jo include Republic of Korea Army.

An enhanced transform domain communication system (ETDCS) with narrow-band interference (NBI) avoidance capability

Abstract: Reliable communication over hostile environment is desired by both military and civilian parties. In this paper, we propose an enhanced transform domain communication system (ETDCS) with narrow-band interference (NBI) avoidance capability. The basic idea for this system is to synthesize adaptive waveform in the frequency domain by a non-parametric spectral estimator, called Capon's method, at both the transmitter and the receiver to avoid spectrally crowded regions. This approach offers better bit error performance than existing similar systems such as the transform domain communication system (TDCS) that utilizes a parametric autoregressive (AR) spectral estimator, the wavelet domain communication system (WDCS) which uses wavelet domain periodogram, or the enhanced wavelet domain communication system (EWDCS) which employs the evolutionary wavelet spectrum (EWS). Specifically, our proposed ETDCS significantly improves the bit error performance under non-stationary interference such as swepttone interference while achieving consistent bit error performance under stationary interference such as partial band, singletone, and multitone interference. Hence, our proposed ETDCS provides a viable alternative for highly reliable communication in interference rich communication environments.

On cracking direct-sequence spread-spectrum systems

Abstract: Secure transmission of information over hostile wireless environments is desired by both military and civilian parties. Direct-sequence spread-spectrum (DS-SS) is such a covert technique resistant to interference, interception, and multipath fading. Identifying spread-spectrum signals or cracking DS-SS systems by an unintended receiver (or eavesdropper) without a priori knowledge is a challenging problem. To address this problem, we first search for the start position of data symbols in the spread signal (for symbol synchronization); our method is based on maximizing the spectral norm of a sample covariance matrix, which achieves smaller estimation error than the existing method of maximizing the Frobenius norm. After synchronization, we remove a spread sequence by a cross-correlation based method, and identify the spread sequence by a matched filter. The proposed identification method is less expensive and more accurate than the existing methods. We also propose a zigzag searching method to identify a generator polynomial that reduces memory requirement and is capable of correcting polarity errors existing in the previous methods. In addition, we analyze the bit error performance of our proposed method. The simulation results agree well with our analytical results, indicating the accuracy of our analysis in additive white Gaussian noise (AWGN) channel. By simulation, we also demonstrate the performance improvement of our proposed schemes over the existing methods. Copyright © 2009 John Wiley & Sons, Ltd. To eavesdrop on the adversary's communication, we (a) identify the start position of data symbols in the intercepted spread signal for the purpose of symbol synchronization, (b) estimate data symbols, (c) estimate the PN sequence, and (d) estimate the code generator polynomial of the PN sequence. We propose a zigzag searching method to identify a generator polynomial from intercepted signal and we also analyze the bit error performance of our proposed method.

Blind synchronization, estimation of data symbol, spread sequence, and generator polynomial in direct sequence spread spectrum systems

Abstract: Secure transmission of information over hostile wireless environments is desired by both military and civilian parties. Direct-sequence spread spectrum (DS-SS) is such a covert technique resistant to interference, interception and multipath fading. Identifying spread-spectrum signals by an unintended receiver (or eavesdropper) without a priori knowledge is a challenging problem. To address this problem, we first search the start position of a data symbol in the spread signal (for synchronization); our method is based on maximizing spectral norm of a covariance matrix, which achieves smaller estimation error than the existing method of maximizing Frobenius norm. After synchronization, we remove information symbols by a cross-correlation based method, and identify the spread sequence by a matched filter. The proposed identification method is less expensive and more accurate than the existing methods. We also propose a zigzag searching method to identify a generator polynomial that reduces memory requirement and is capable of correcting polarity errors existing in the previous methods. Our simulation results validate the effectiveness of our proposed method.

An enhanced V-BLAST with non-stationary interference avoidance capability

Abstract: Reliable communication under interferences is desired by both military and commercial parties. This paper proposes a vertical-Bell Laboratories Layered Space-Time (V-BLAST) architecture with non-stationary interference avoidance capability. A transform domain processing (TDP) and minimum mean square error (MMSE) detector are combined with the V-BLAST to enhance performance in a narrow band interference (NBI) environment. A key idea of TDP is to generate an adaptive modulated information-bearing signal avoiding spectrally crowded regions in the transform domain at both transmitters and receivers of the V-BLAST system. The adaptive interference-free signal is synthesized by a non-parametric spectral estimator, called Caponpsilas method (CM). The proposed V-BLAST system also incorporates the MMSE detector. These approaches offer better bit error performance than other interference mitigation methodologies that process signals at the receiver only, and better than other similar systems that use a parametric spectral estimator with zero-forcing detector. Our simulation results indicate that the proposed system mitigates not only stationary interferences but also non-stationary interferences. Therefore, the proposed system is a viable option for the highly reliable multiple-input multiple-output (MIMO) system.

On the performance of joint space‐frequency pre‐filtering and equalization for downlink multi‐carrier code division multiple access

Abstract: We analyze the performance of joint space-frequency pre-filtering and equalization techniques for downlink multi-carrier code division multiple access in terms of average bit error rate performance. Several linear power allocation strategies combined with single-user equalization schemes are compared with a joint pre-filtering with an equal power constraint at the base station and maximal ratio combining at the mobile terminals. Our bit error rate analysis obtained in this paper facilitates predicting the performance of various space-frequency pre-filtering schemes without massive simulations. Copyright © 2011 John Wiley & Sons, Ltd.

Spread Spectrum Pattern and PN Sequence Retrieval in Wireless Ad Hoc Network: Design Approach

Abstract: Spread spectrum signaling technique is used for security purpose in wireless network because it becomes difficult to access the wireless network by unwanted users. We are developing the algorithm to retrieve the PN sequence & pattern of spectrum in spread spectrum system. This algorithm will increase the wireless network security & solve the problem of accessing the wireless network in secured way. Because, when only sender end knows the PN sequence & pattern of spread spectrum communication system the network security will be enhanced. Spread spectrum is a means of transmission in which data sequence occupies a much more bandwidth than minimum required bandwidth necessary to send it. The spectrum spreading at transmitter & de-spreading at receiver is obtained by PN-sequence which is independent of data sequence. There are two types of the spread spectrum techniques direct sequence spread spectrum & frequency hopped spread spectrum. Direct sequence spread spectrum is technique in which data sequence directly modulates the pseudo noise sequence known to only transmitter & receiver. Frequency hopping means to transmit data in different frequency slots.

Contributions to time-frequency synchronization in wireless systems

Abstract: Time and frequency synchronization is an indispensable task for all wireless transceivers and systems. In modern wireless systems, such as 4G and future 5G systems, new wireless technologies set new challenges also to synchronization. In particular, new solutions for time and frequency synchronization are needed in multiantenna and cooperative systems. New research areas arise also in context of interference cancellation and cognitive radio systems where the transmission parameters of the signal of interest may not be known to the receiver. Similar applications can be found also in the military domain. Obviously, synchronization in such cases poses significant challenges. In this thesis, new methods for time and frequency synchronization in wireless systems are developed and analyzed. Both orthogonal frequency division multiplexing (OFDM) -based as well as direct sequence spread spectrum (DSSS) -based systems are considered. The thesis consists of seven publications and a summary which contains also an extensive literature review on the topic. Synchronization acquisition methods in DSSS-based systems without the knowledge of the spreading sequence are developed. A subspace -based method for asynchronous multi-user DSSS systems is proposed and shown to achieve nearly optimal processing gain corresponding to that of the conventional matched filter. The studied methods find applications in interference cancellation, cognitive radio as well as in military applications. Multiantenna methods for synchronization are analyzed. Probabilities of synchronization acquisition and false alarm are derived analytically for the multiantenna case where transmit, receive and time diversity schemes are used. The analytical results are verified by simulations. Also optimum synchronization sequence transmission schemes are derived. Extensive simulation results for various scenarios in terms of signal-to-noise ratio, spatial correlation and Doppler spread are provided. The results can be used to facilitate practical design of wireless multiantenna systems. The impacts of time and frequency offsets in cooperative OFDM wireless systems are analyzed and quantified and shown to be, in some cases, much more severe than in traditional OFDM systems. Solutions to estimation of multiple frequency offsets in cooperative OFDM systems are then studied. A method enabling low complexity algorithms to be used for the estimation is proposed and shown to achieve mean square error performance close to the Cramer-Rao bound.; Aika- ja taajuussynkronointi on oleellinen toiminto kaikissa langattomissa vastaanottimissa ja jarjestelmissa. Nykyaikaisissa langattomissa jarjestelmissa, kuten 4G- seka tulevissa 5G-jarjestelmissa, uudet langattomat teknologiat asettavat uusia haasteita myos synkronoinnille. Uusia synkronointiratkaisuja tarvitaan erityisesti moniantennijarjestelmissa seka yhteis-toiminnallisissa jarjestelmissa. Joissain sovelluksissa, esimerkiksi hairionpoistossa ja kognitiivisissa radioissa, synkronointi on tehtava vastaanottimessa tuntematta…

On Narrowband Interference Suppression in TDCS with WFRFT Preprocessing

Abstract: We propose a modified transform domain communication system (TDCS) structure with weighted fractional Fourier transform (WFRFT) preprocessing over the channel with additive white Gaussian noise (AWGN) and narrowband interference (NBI). The majority of NBI can be removed by adding zeros to TDCS’s basic function (BF) amplitude vector at these subcarriers where strong NBI exists, and the corresponding residual NBI can be further greatly eliminated in time-frequency domain through WFRFT processing. To achieve the best bit error rate (BER) performance, we define as the normalised cross relationship coefficient between TDCS’s BF vector and residual NBI vector and prove that the corresponding WFRFT can be obtained by minimising the magnitude of . Numerical simulations are conducted to evaluate the proposed system’s performance with regard to NBI suppression.

On the modulation and signalling design for a transform domain communication system

Abstract: Transform domain communication system (TDCS) has been proposed to establish a communication link with a low probability of interception by synthesising an adaptive waveform containing energy only in the unused frequency bands. However, this communication system suffers from a low spectral efficiency. To improve its spectral efficiency, a unified modulation framework for a TDCS is proposed in this study to embrace the previously reported modulation schemes under one framework. The resulting spectral efficiency is higher compared to these previous schemes. Also, to combat the slow channel fading, a TDCS system using two transmit antennas and one receive antenna with the proposed modulation scheme is presented. Simulation results show that the multiple-antenna system improves the performance dramatically compared to the single antenna system under the slow fading environment.

IPsec tunnels vs. identity-only obfuscation techniques for moving target networks

Abstract: There has been recent interest in applying moving target approaches to computer networks. The ability to obfuscate the adversary's view of an organization's internal network is thought to confound the adversary's network reconnaissance steps, causing certain inefficiencies in nation state actors' attack processes. Novel Moving Target Network (MTN) techniques have been proposed specifically to hide communicating endpoint identities, blinding the adversary's view of the nodes in the network. To date, however, no published work has evaluated identity-only obfuscation approaches against using IPsec ESP tunnels as a way of hiding endpoint identities. The question is, are there some network configurations where identity-only obfuscation techniques work better than IPsec ESP tunnels? We present arguments that low-overhead MTN identity-only obfuscation approaches may work more efficiently on wireless mobile, tactical, peer-to-peer networks where processing energies and transmission bandwidth are constrained and we also discuss features of metrics for measuring the success of moving target network approaches, helping to guide future research in this area.