MS, University of Cincinnati, 2002, Engineering : Electrical Engineering

Multicarrier CDMA has emerged recently as a promising candidate for the next generation broad-band mobile networks. Since multicarrier CDMA combines the multicarrier technique and the spread-spectrum CDMA technique, many multiuser detection methods used in DS-CDMA can be applied to multicarrier CDMA system. In this thesis, we propose a direct blind multiuser detection method for multicarrier CDMA based on linear prediction. Using only the spreading code of the desired user, we extract the column vector subspace corresponding to the signal of interest from the channel matrix of the received complex signal. And then zero-forcing (ZF) and minimum mean square error (MMSE) detectors are constructed. Our algorithms do not require channel estimation and avoid the channel estimation error. Simulations show that in most conditions, our algorithms outperform the typical subspace-based algorithm and the eigen-method used in a multicarrier system.

Committee: Dr. Howard Fan (Advisor) Subjects:

PhD, University of Cincinnati, 2004, Engineering : Electrical Engineering

As demand for higher data rates is continuously rising, there is always a need to develop more efficient wireless communication systems. The work described in this thesis is our effort in this direction. We have developed and evaluated a wavelet packet based multicarrier CDMA wireless communication system. In this system design a set of wavelet packets are used as the modulation waveforms in a multicarrier CDMA system. The need for cyclic prefix is eliminated in the system design due to the good orthogonality and time-frequency localization properties of the wavelet packets. New detection algorithms are developed to work in either time domain or wavelet packet domain to combat multiuser and inter symbol interferences. Better performance is achieved by utilizing the saved cyclic prefix overhead for error correction coding. In developing the above system and detection algorithms, we also explored a new method of channel modeling by using wavelet packets as basis functions.

Committee: Dr. Howard Fan (Advisor) Subjects:

Doctor of Philosophy, The Ohio State University, 2010, Electrical and Computer Engineering

We consider the problem of practical communication over a doubly selective (DS)channel, i.e., a time and frequency selective channel. The problem is approached in two different ways: coherent communication and noncoherent communication, and for each communication scheme we propose practical and near-optimal equalizers and maximum-diversity precoders. Toward these ends, we adopt 1) basis expansion (BE) modeling of the channel, which allows for an efficient and unied way of describing a DS channel in both time and frequency domain; and 2) tree-search algorithms (TSAs), which facilitate near-optimal performance with low complexity.For practical coherent communication, we focus on the pulse-shaped (PS) multicarrier modulation (MCM), where controlled inter-symbol-interference (ISI) and inter-carrier-interference (ICI) can be leveraged for computationally efficient receiver structures. Then, we propose a novel channel adaptive TSA with a novel fast minimum mean-squared error (MMSE) generalized decision-feedback equalizer (GDFE) preprocessing, and a rank-reduced channel estimation by using the BE channel model. Also, a new finding about optimality of MMSE-GDFE preprocessing is presented, which states that under constant modulus constellation the minimum distance property is preserved by the MMSE-GDFE preprocessing. Then, two practically realizable noncoherent equalization schemes are proposed: a sequential algorithm and a Bayesian expectation maximization (EM)-based algorithm. The sequential algorithm is derived from the optimal noncoherent metric, and made practical by a fast algorithm and a TSA to evaluate and search over the metric. The Bayesian EM-based noncoherent algorithm is derived from optimal maximum a posteriori (MAP) estimation of the BE parameters, and efficiently implemented via iteration between soft coherent equalizer and soft channel estimator. Efficient operations are accomplished using fast algorithms whose overall complexities grow linearly in the block (open full item for complete abstract)

Committee: Phil Schniter (Advisor); Hesham El-Gamal (Committee Member); Lee Potter (Committee Member) Subjects: Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2008, Electrical Engineering

In the near future, the need for portable multi-antenna wireless devices supporting high data-rates in a harsh mobile environment is anticipated. Typically, in this scenario, the underlying wireless channels are time- and frequency selective, hence doubly selective (DS). Multicarrier modulation (MCM) schemes, wherein a stream of data is split into sub-streams and transmitted on a set of subcarriers in parallel, is frequently used on wireless communication systems. DS channels generate both inter-symbol interference (ISI) as well as inter-carrier interference (ICI) for MCM transmissions, thereby making the design of MCM receivers a challenging task. The challenge is compounded by strict constraints on processing power as a result of the demand for light, portable, low-power devices, and by the lack of channel state information (CSI) in practical wireless receivers. On one hand, information-theoretic analysis of MCM systems has focused on the performance of optimal MCM reception without complexity constraints. On the other hand, practical MCM receiver designs use sub-optimal techniques requiring limited processing power. Moreover, the performance limits of these practical designs is seldom compared to what is promised by optimal reception. Local subcarrier processing (LSP) using CSI acquired via pilot-aided channel estimation is arguably the most popular practical MCM receiver design technique. The LSP constraint allows the use of only a small subset of local observations and dominantICI coefficients to retrieve information transmitted on each subcarrier. We characterize the performance limits imposed by LSP-constrained reception on generic MCM schemes. Our approach provides a new framework within which the performance limits of practical reception strategies with processing complexity constraints can be characterized and compared to optimal reception for any MCM scheme.

Committee: Philip Schniter (Advisor) Subjects:

Doctor of Philosophy (PhD), Ohio University, 2010, Electrical Engineering (Engineering and Technology)

In this dissertation, we propose a new transmission scheme called frequency generalized multicarrier code division multiple access (FG-MC-CDMA) for future wireless communications. The FG-MC-CDMA system uses multi-code and concatenated-codes to provide users flexible data rates and a range of system performance to satisfy the variable service QoS requirements for multimedia applications. FG-MC-CDMA performance is evaluated on both single band and multiband (MB) channel conditions. We also propose the use of multiband channels in future wireless communication systems to alleviate the problem of radio spectrum scarcity. Multiband channels are classified into three different categories based on the frequency separation of different sub-bands. MC-CDMA systems, including the FG-MC-CDMA system, can be easily designed to work on multiband channels. In the MC-CDMA multiband application, we study the single-user transmitted power allocation problem to explore the effects of multi-band diversity. The optimal (minimum BER) power allocation algorithm with the restriction of a fixed transmitted power is derived, and analytical BER expressions for this optimal power allocation are provided. We also propose to use multi-level orthogonal (MLO) codes in MC-CDMA to exploit frequency diversity further. With maximum likelihood sequence detection (MLSD), MLO codes are shown to provide much better system performance than traditional binary orthogonal codes. In the last part, we briefly cover the performance impairment factors to FG-MC-MCDA systems and use channel estimation as an example to demonstrate that accurate system performance can only be evaluated with careful considerations of all factors in real applications.

Committee: David W. Matolak PhD (Committee Chair); Jeffrey Dill PhD (Committee Member); Roger Radcliff PhD (Committee Member); Trent Skidmore PhD (Committee Member); Wei Lin PhD (Committee Member); Dinh V. Huynh PhD (Committee Member) Subjects:

Doctor of Philosophy (PhD), Ohio University, 2000, Electrical Engineering & Computer Science (Engineering and Technology)

In this dissertation, a novel wavelet packet based multicarrier modulation CDMA system is proposed and analyzed. Properties of wavelets and wavelet packets are investigated, the concept of wavelet packet modulation is then explained. Based on this concept, a wavelet packet based multicarrier modulation CDMA transceiver structure is proposed. Compared with three conventional sinusoids based multicarrier CDMA systems, the proposed system has the same computation complexity, consumes much less system resource while achieves the same performance and system capacity. System performance of the proposed system are investigated in two different channels. In the AWGN channel, two anti-jamming algorithms are developed for the proposed system. First, the simplified super-symbol tuning algorithm for known jamming suppression is developed. By taking advantage of the knowledge of the system and jamming signal, the one-direction tuning algorithm can achieve the same performance as the algorithm using both forward and reverse tuning, therefore, greatly simplifies the system. Second, in a system with unknown narrow band jamming signals, generalized Fisher's test algorithm is developed. Due to the time-frequency compact support property of wavelet packets, narrow band jamming signal can be easily detected by using wavelet packet transform and inverse transform pair. Numerical results show that generalized Fisher's test algorithm can suppress the jamming signal in a large jamming to noise ratio range with large jamming signal bandwidth variation. In the slow fading frequency selective channel, maximal ratio combining and equal gain combing equalization techniques under both synchronous and asynchronous situations are investigated. From both theoretical analysis and numerical result, it is shown that maximal ratio combining equalization outperforms the equal gain combining equalization. Based on all the analysis and results, it is clear that wavelet packet based multi-carrier modulatio (open full item for complete abstract)

Committee: Jeffrey Dill (Advisor) Subjects:

Doctor of Philosophy (PhD), Ohio University, 2007, Electrical Engineering & Computer Science (Engineering and Technology)

In the work of this dissertation, we propose a new modulation scheme called spectrally-shaped generalized multitone direct-sequence spread spectrum (SSG-MT-DS-SS) which is the generalized multitone/multicarrier-DS-SS (MC/MT-DS-SS) scheme. With SSG-MT-DS-SS, we can shape the spectrum of the transmitted signal with out using any kind of pulse shape filter. The spectral shaping is achieved via allowing the data rate, bit energy, processing gain, and carrier frequency of each subcarrier to be adjustable. Specifically, the parameters of each subcarrier are not constrained to be identical as conventional MC/MT-DS-SS schemes. By varying these parameters, we alter the energy distribution of the SSG-MT-DS-SS signal, and, hence, the spectrum of the transmitted signal. In this dissertation, we investigate the spectral shaping mechanism and the shaping capabilities of SSG-MT-DS-SS. We provide a general form of the power spectrum density of SSG-MT-DS-SS with arbitrary parameters on each subcarrier, and develop a numerical method to select the parameters of SSG-MT-DS-SS according to some given design requirements. We derive the general form of the bit error probability SSG-MT-DS-SS in additive white Gaussian noise channel and the dispersive channel. In addition, we also investigate the error performance of SSG-MT-DS-SS with sinusoidal chip waveforms on each subcarrier. It is shown that with the properly selected sinusoidal chip waveform and the dual sidebands combining scheme, we can improve the error performance of SSG-MT-DS-SS in the dispersive channel. The use of error correction code, e.g., Hamming code, and the peak to average power ratio of the SSG-MT-DS-SS are also investigated in this dissertation.

Committee: David Matolak (Advisor) Subjects:

Master of Science (MS), Ohio University, 2004, Electrical Engineering & Computer Science (Engineering and Technology)

We provide new analytical and computer simulation results for the performance of multitone direct-sequence spread spectrum (MT-DS-SS) signaling in the presence of imperfect synchronization, modeled as frequency offset and phase noise. We investigate performance as a function of frequency offset/phase noise standard deviation, number of subcarriers and the per-subcarrier processing gain. We assume coherent detection with BPSK modulation. Comparisons between simulations and analysis show excellent agreement. Our approach offers a realistic analytical/numerical method for performance evaluation when the target error probability values are of the order of 10 −6 or lower. In addition, our method can also be easily applied to any multicarrier system with other frequency offset/phase noise models.

Committee: David Matolak (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2006, Electrical Engineering

As the demand for transmitting variable and high data rates rises, the need to develop more efficient wireless communication systems increases. In this dissertation, a new Wavelet Packets based Multicarrier Multicode Code Division Multiple Access (WP-MC/MCD-CDMA) system, which combines the properties of wavelet packets with the concept of MC, MCD and CDMA, is proposed and analyzed. Another new wavelet packets based system, denoted as Wavelet Packets Multicarrier Multiuser Code Division Multiple Access (WP-MC/MU-CDMA) system, which combines the properties of wavelet packets with the concept of MC and CDMA, is proposed and analyzed. The WP-MC/MCD-CDMA can be used for multirate services using multicode schemes. In WP-MC/MU-CDMA system, a decorrelating suboptimum detector is used in the detection process. This will suppress the multiple access interference, support a higher number of users and relaxes the power control requirements. In our systems, wavelet packets functions are used as subcarrier instead of a sinusoidal function. Thus, the proposed systems have high immunity against interferences caused by multipath and multicarriers. The systems are evaluated in Nakagami slow fading channel, and their performance are investigated in terms of signal-to-noise plus interference ratio, bit error rate and outage probability. Three diversity combiners, namely selective diversity, equal gain combining and maximal ratio combining are used at the receiver to improve the system performance. Results show that the new proposed systems are viable for future generation wireless systems.

Committee: Okechukwu Ugweje (Advisor) Subjects: