Copyright (c) 2013 San Jose State University All rights reserved. http://scholarworks.sjsu.edu/ee_pub Recent documents in Faculty Publications en-us Tue, 14 May 2013 16:10:51 PDT 3600 http://scholarworks.sjsu.edu/ee_pub/33 http://scholarworks.sjsu.edu/ee_pub/33 Wed, 23 Mar 2011 16:21:27 PDT A non-data aided carrier recovery technique using digital modulation format identification called multi-mode PLL (Phase Locked Loop) is proposed. This technique can be interpreted as a modulation identification method that is robust against static phase and frequency offsets. The performance of the proposed technique is studied and the analytical expressions are derived for the probability of lock detection, acquisition time over AWGN channel in the cases of M-PSK and M-QAM modulations with respect to frequency offset and signal-to-noise ratio.

]]> Kenta Umebayashi et al. http://scholarworks.sjsu.edu/ee_pub/32 http://scholarworks.sjsu.edu/ee_pub/32 Thu, 17 Mar 2011 16:19:40 PDT In this paper, an adaptive adjacent channel interference (ACI) technique is proposed. Results for BPSK modulation with rectangular and square-root raised-cosine pulse shaping, under AWGN conditions, are obtained showing the proposed method to be effective in improving performance under high levels of interference. Basically, the idea is to send pilot signals and then to use them in estimating the amount of ACI in the frequency domain. The estimated spectral error is used to modify tap weights of an adaptive frequency-domain filter. Our simulation results reported suggest that ACI can be effectively reduced with the proposed technique. At the system level, the requirements of analog front-end channel-select and other filters can be relaxed, resulting in a cost -effective receiver design.

]]> Robert H. Morelos-Zaragoza et al. http://scholarworks.sjsu.edu/ee_pub/30 http://scholarworks.sjsu.edu/ee_pub/30 Fri, 11 Feb 2011 08:26:07 PST In this paper, theoretical upper bounds and computer simulation results on the error performance of multilevel block coded modulations for unequal error protection (UEP) and multistage decoding are presented. It is shown that nonstandard signal set partitionings and multistage decoding provide excellent UEP capabilities beyond those achievable with conventional coded modulation. The coding scheme is designed in such a way that the most important information bits have a lower error rate than other information bits. The large effective error coefficients, normally associated with standard mapping by set partitioning, are reduced by considering nonstandard partitionings of the underlying signal set. The bits-to-signal mappings induced by these partitionings allow the use of soft-decision decoding of binary block codes. Moreover, parallel operation of some of the staged decoders is possible, to achieve high data rate transmission, so that there is no error propagation between these decoders. Hybrid partitionings are also considered that trade off increased intraset distances in the last partition levels with larger effective error coefficients in the middle partition levels. The error performance of specific examples of multilevel codes over 8-PSK and 64-QAM signal sets are simulated and compared with theoretical upper bounds on the error performance.

]]> Robert H. Morelos-Zaragoza et al. http://scholarworks.sjsu.edu/ee_pub/29 http://scholarworks.sjsu.edu/ee_pub/29 Fri, 04 Feb 2011 10:11:12 PST This paper considers iterative decoding of two-level superposition codes used in cooperative broadcasting over wireless networks. The coding scheme consists of two low-density parity-check (LDPC) codes combined using Plotkin's |u|u + v|-construction and provides two levels of error protection. Coding for cooperative broadcasting differs from conventional single-source broadcast coding. Instead of binary addition of subcode codewords performed by a single-source encoder, in superposition coding two modulated subcode sequences, produced by two coordinated and independent sources, are combined at the antenna of the receiver. Expressions are derived for the bit metrics, or log-likelihood ratio values, used by an iterative decoder for two-level superposition coding schemes based on BPSK, QPSK and 4-PAM modulated sequences. It is shown that conventional equal-energy 4-PAM constellations do not work well with two-level superposition coding. A solution is proposed in which 4-PAM constellations of different levels of average energy are used.

]]> Robert H. Morelos-Zaragoza http://scholarworks.sjsu.edu/ee_pub/28 http://scholarworks.sjsu.edu/ee_pub/28 Fri, 04 Feb 2011 09:26:49 PST This talk is aimed at MSEE students in San Jose State University. It provides an overview of cognitive radio concepts and technologies. A MATLAB Simulink of demonstration of digital channel selection using a low IF radio architecture is presented. Technical challenges that remain to be solved in this area are identified.

]]> Robert H. Morelos-Zaragoza http://scholarworks.sjsu.edu/ee_pub/27 http://scholarworks.sjsu.edu/ee_pub/27 Fri, 04 Feb 2011 09:17:46 PST In this talk, the unique characteristics of ultra wideband (UWB) communications systems are introduced. Receiver design considerations are presented. Focus is on the relation between the symbol duration and the delay spread of the channel. This determines whether the receiver should use a Rake receiver (Spread-spectrum system) or an equalizer (multiple carrier or OFDM system).

]]> Robert H. Morelos-Zaragoza http://scholarworks.sjsu.edu/ee_pub/26 http://scholarworks.sjsu.edu/ee_pub/26 Fri, 04 Feb 2011 08:53:16 PST Robert H. Morelos-Zaragoza et al. http://scholarworks.sjsu.edu/ee_pub/25 http://scholarworks.sjsu.edu/ee_pub/25 Thu, 03 Feb 2011 10:28:28 PST This talk considers the design and implementation of error correcting codes for cooperative broadcasting in wireless networks. Focus is on the case of two cooperating sources transmitting two classes of information to a single receiver. This case was first introduced in the seminal work of Bergmans and Cover and referred to as "over the air mixing". Two levels of protection are provided using two low-density parity-check (LDPC) codes combined using Plotkin's |u|u+v|-construction. Expressions are derived for the bit metrics used in iterative decoding for two-level codes combined with BPSK, QPSK and 4-PAM modulations. Several examples of codes and their performance over AWGN and flat Rayleigh fading channels are presented. The talk concludes with final remarks and directions for future research in this area.

]]> Robert H. Morelos-Zaragoza http://scholarworks.sjsu.edu/ee_pub/24 http://scholarworks.sjsu.edu/ee_pub/24 Wed, 19 Jan 2011 10:49:33 PST Cognitive radios aim to coexist in the unused spectrum bands which are licensed to primary users without harming the primary transmission/reception. For a cognitive radio, it is important to detect the band in which the primary is operating as fast as possible and with high reliability in order to adapt its transmission. In this work, we propose P-partitioning method in combination with energy detectors for the search of the band that the primary user is operating. In the P-partitioning method, the spectrum bands are categorized into P groups and the group that the primary band belongs to is detected in a recursive fashion. The energy detector operates on each group and the test statistics is the total energy received in the bands belonging to the group. The proposed search technique has detection time PlogP(N), where N is the number of bands in the spectrum. When P = N, the proposed scheme is equivalent to linear search with detection time N. We study the performance of the proposed scheme for a single non-cooperative radio and also for multiple cooperating radios. For a single cognitive radio, we provide an upper bound on the probability of correct detection which presents two different regimes of operation. In the low SNR regime, although it is counter-intuitive the partitioning improves the probability of detection. This is due an averaging effect when the signal energy in different bands are accumulated to obtain the energy contribution from a group. In the high SNR regime, performance degrades with partitioning. In addition, we observe that user cooperation improves the performance in the high SNR regimes.

]]> Birsen Sirkeci-Mergen et al. http://scholarworks.sjsu.edu/ee_pub/23 http://scholarworks.sjsu.edu/ee_pub/23 Wed, 19 Jan 2011 10:35:03 PST In this paper, a study is presented of the dynamic behavior of an automatic transmit power control (ATPC) loop in a single fixed wireless system (FWS) link subject to multipath fading and an uncorrelated co-channel interferer that does not use ATPC (this represents a so-called non-ATPC FWS link or a fixed satellite link). Fundamental questions include the sensitivity of an ATPC link to multipath interference and the co-channel interference that may be caused by a non-ATPC interferer. In the context of the present project, a good example of a non-ATPC interferer is a fixed satellite to which one antenna in a fixed microwave link has partial view. A computer model was developed that constitutes a useful tool in describing; simulating and analyzing an ATPC loop in a single FWS link. With the aid of this model, results are presented on the sensitivity of an ATPC loop in a FWS link with respect to channel conditions, non-ATPC interference and parameter settings.

]]> Robert H. Morelos-Zaragoza et al. http://scholarworks.sjsu.edu/ee_pub/22 http://scholarworks.sjsu.edu/ee_pub/22 Wed, 19 Jan 2011 10:24:34 PST We introduce the modulation identification technique implementing the multimode phase locked loop (PLL) in the satellite communication using adaptive modulation scheme which is a countermeasure against the rain attenuation. In the multimode PLL, phase lock detectors (PLDs) are used for not only phase lock, but also modulation identification. We present the sub-optimized design of the PLDs for modulation identification with respect to the throughput and show the validity of sub-optimization. In addition, by the comparison between the multimode PLL and conventional scheme in ISDB-S, we present the effectivity of the multimode PLL.

]]> Kenta Umebayashi et al. http://scholarworks.sjsu.edu/ee_pub/21 http://scholarworks.sjsu.edu/ee_pub/21 Wed, 19 Jan 2011 10:09:03 PST In this paper, the performance of adaptive equalization and turbo product coding is investigated for pulse-based UWB communications in short-range indoor environments. The sensitivity of adaptive LMS linear and nonlinear (decision-feedback) equalizers with respect to the number of training symbols and number of taps is considered. To reduce the error performance variation with respect to changing channel conditions, a turbo product code (TPC) with two component (31,26,3) Hamming codes is proposed. We report simulation results showing that channel coding not only improves error performance, but also reduces significantly the sensitivity of UWB systems in short-range indoor wireless communications.

]]> Robert H. Morelos-Zaragoza et al. http://scholarworks.sjsu.edu/ee_pub/20 http://scholarworks.sjsu.edu/ee_pub/20 Wed, 19 Jan 2011 09:55:54 PST We continue our investigation of joint beamforming and transmit diversity with space-time block coding. In particular, the performance of a four-element array antenna is considered, in the context of an indoor wireless communication system. The main contribution is to show that transmit diversity may be practically achieved, even with correlated beams produced by a sparse array antenna.

]]> Robert H. Morelos-Zaragoza et al. http://scholarworks.sjsu.edu/ee_pub/19 http://scholarworks.sjsu.edu/ee_pub/19 Tue, 18 Jan 2011 17:11:22 PST A two-stage decoding procedure for pragmatic trellis-coded modulation (TCM) is introduced. It applies a transformation from the received I-channel and Q-channel samples onto points in a two-dimensional (2-D) signal space that contains a coset constellation. For pragmatic TCM over M-PSK signal sets with ν coded bits per symbol, ν=1, 2, the signal points in the coset constellations represent cosets of a B/QPSK signal subset-associated with the coded bits-in the original M-PSK signal constellation. A conventional Viterbi decoder operates on the transformed symbols to estimate the coded bits. After reencoding these bits, the uncoded bits are estimated in a second stage, on a symbol-by-symbol basis, with decisions based on the location of the received symbols. In addition to requiring no changes in the Viterbi decoder core, it is shown that the proposed method results in savings of up to 40% in the memory required to store (or in the size of the logic required to compute) metrics and transformed symbols.

]]> Robert H. Morelos-Zaragoza et al. http://scholarworks.sjsu.edu/ee_pub/18 http://scholarworks.sjsu.edu/ee_pub/18 Tue, 18 Jan 2011 17:01:10 PST A new software defined radio platform with multiport-based direct conversion is proposed, named SOPRANO (Software Programmable and Hardware Reconfigurable Architecture for Network). The main features of SOPRANO are a high-level design methodology for digital circuits, a new mixer-less direct conversion method, and software algorithms for multi-band and multi-mode operation. We built the first prototype SOPRANO 1.0, which was able to receive PSK and QAM signals with two different carrier frequencies at 2.45 GHz and 5.25 GHz by changing signal processing software.

]]> Shinichiro Haruyama et al. http://scholarworks.sjsu.edu/ee_pub/17 http://scholarworks.sjsu.edu/ee_pub/17 Tue, 18 Jan 2011 16:45:39 PST Recent research activities in the area of mobile radio communications have moved to third generation (3G) cellular systems to achieve higher quality with variable transmission rate of multimedia information. In this paper, an overview is presented of various interference cancellation and iterative detection techniques that are believed to be suitable for 3G wireless communications systems. Key concepts are space-time processing and space-division multiple access (or SDMA) techniques. SDMA techniques are possible with software antennas. Furthermore, to reduce receiver implementation complexity, iterative detection techniques are considered. A particularly attractive method uses tentative hard decisions, made on the received positions with the highest reliability, according to some criterion, and can potentially yield an important reduction in the computational requirements of an iterative receiver, with minimum penalty in error performance. A study of the tradeoffs between complexity and performance loss of iterative multiuser detection techniques is a good research topic.

]]> Ryuji Kohno et al. http://scholarworks.sjsu.edu/ee_pub/16 http://scholarworks.sjsu.edu/ee_pub/16 Tue, 18 Jan 2011 16:34:15 PST A non-data aided carrier recovery technique using modulation format identification is proposed. This technique can also be interpreted as a modulation identification method that is robust against static phase and frequency offsets. The performance of the proposed technique is studied and analytical expressions derived for the mean acquisition time to detect lock in the cases of M-PSK, M=2,4,8, and 16-QAM modulation, with respect to frequency offset and signal-to-noise ratio. The results are verified with Monte Carlo simulations. The main advantage of the proposed method lies in its simpler implementation and faster lock detection, when compared to conventional methods.

]]> Robert H. Morelos-Zaragoza et al. http://scholarworks.sjsu.edu/ee_pub/15 http://scholarworks.sjsu.edu/ee_pub/15 Tue, 18 Jan 2011 16:19:38 PST In this paper, multilevel coded asymmetric modulation with multistage decoding and unequal error protection (UEP) is discussed. These results further emphasize the fact that unconventional signal set partitionings are more promising than traditional (Ungerboeck-type) partitionings, to achieve UEP capabilities with multilevel coding and multistage decoding. Three types of unconventional partitionings are analyzed for asymmetric 8-PSK and 16-QAM constellations over the additive white Gaussian noise channel to introduce design guidelines. Generalizations to other PSK and QAM type constellations follow the same lines. Upper bounds on the bit-error probability based on union bound arguments are first derived. In some cases, these bounds become loose due to the large overlappings of decision regions associated with asymmetric constellations and unconventional partitionings. To overcome this problem, simpler and tighter approximated bounds are derived. Based on these bounds, it is shown that additional refinements can be achieved in the construction of multilevel UEP codes, by introducing asymmetries in PSK and QAM signal constellations.

]]> Motohiko Isaka et al. http://scholarworks.sjsu.edu/ee_pub/14 http://scholarworks.sjsu.edu/ee_pub/14 Tue, 18 Jan 2011 15:56:40 PST This paper considers block-coded 8-phase-shift-keying (PSK) modulations for the unequal error protection (UEP) of information transmitted over Rayleigh-fading channels. Both conventional linear block codes and linear UEP (LUEP) codes are combined with a naturally labeled 8-PSK signal set, using the multilevel construction of Imai and Hirakawa (1977). Computer simulation results are presented showing that, over Rayleigh-fading channels, it is possible to improve the coding gain for the most significant bits with the use of binary LUEP codes as constituent codes, in comparison with using conventional binary linear codes alone.

]]> Robert H. Morelos-Zaragoza et al. http://scholarworks.sjsu.edu/ee_pub/13 http://scholarworks.sjsu.edu/ee_pub/13 Tue, 18 Jan 2011 15:34:05 PST Binary multilevel convolutional codes (CCs) with unequal error protection (UEP) capabilities are studied. These codes belong to the class of generalized concatenated (GC) codes. Binary CCs are used as outer codes. Binary linear block codes of short length, and selected subcodes in their two-way subcode partition chain, are used as inner codes. Multistage decodings are presented that use Viterbi decoders operating on trellises with similar structure to that of the constituent binary CCs. Simulation results of example binary two-level CC's are also reported.

]]> Robert H. Morelos-Zaragoza et al.