Recently proposed full-rate quasi-orthogonal space-time block codes (QSTBCs) with power scaling is able to achieve full-diversity through linearly combining two adequately power scaled orthogonal space-time block codes (OSTBCs). While in our initial work we numerically derived the optimal value of the power scaling factor to achieve full-diversity, our goal in this letter is to analytically derive the optimal power scaling, especially for square lattice constellations (e.g., 4-QAM, 16-QAM, etc.) by maximizing the coding gain.

In this paper, a novel algorithm, Cross Low-dimension Pursuit, based on a new structured sparse matrix, Permuted Block Diagonal (PBD) matrix, is proposed in order to recover sparse signals from incomplete linear measurements. The main idea of the proposed method is using the PBD matrix to convert a high-dimension sparse recovery problem into two (or more) groups of highly low-dimension problems and crossly recover the entries of the original signal from them in an iterative way. By sampling a sufficiently sparse signal with a PBD matrix, the proposed algorithm can recover it efficiently. It has the following advantages over conventional algorithms: (1) low complexity, i.e., the algorithm has linear complexity, which is much lower than that of existing algorithms including greedy algorithms such as Orthogonal Matching Pursuit and (2) high recovery ability, i.e., the proposed algorithm can recover much less sparse signals than even 1-norm minimization algorithms. Moreover, we demonstrate both theoretically and empirically that the proposed algorithm can reliably recover a sparse signal from highly incomplete measurements.

In this paper, we consider a nonparametric regression problem using a learning machine defined by a weighted sum of fixed basis functions, where the number of basis functions, or equivalently, the number of weights, is equal to the number of training data. For the learning machine, we propose a training scheme that is based on orthogonalization and thresholding. On the basis of the scheme, vectors of basis function outputs are orthogonalized and coefficients of the orthogonalized vectors are estimated instead of weights. The coefficient is set to zero if it is less than a predetermined threshold level assigned component-wise to each coefficient. We then obtain the resulting weight vector by transforming the thresholded coefficients. In this training scheme, we propose asymptotically reasonable threshold levels to distinguish contributed components from unnecessary ones. To see how this works in a simple case, we derive an upper bound for the generalization error of the training scheme with the given threshold levels. It tells us that an increase in the generalization error is of O(log n/n) when there is a sparse representation of a target function in an orthogonal domain. In implementing the training scheme, eigen-decomposition or the Gram–Schmidt procedure is employed for orthogonalization, and the corresponding training methods are referred to as OHTED and OHTGS. Furthermore, modified versions of OHTED and OHTGS, called OHTED2 and OHTGS2 respectively, are proposed for reduced estimation bias. On real benchmark datasets, OHTED2 and OHTGS2 are found to exhibit relatively good generalization performance. In addition, OHTGS2 is found to be obtain a sparse representation of a target function in terms of the basis functions.

This paper proposes a windowed-sinc function based peak-to-average power ratio (PAPR) reduction scheme for applying the polar transmitter techniques to orthogonal frequency division multiplexing (OFDM), where the high PAPR problem occurs. The proposed algorithm mitigates the effect of excessive suppression due to successive peaks or relatively high peaks of a signal, which is often observed when applying the conventional peak windowing scheme. The bit error rate (BER) and error vector magnitude (EVM) performances are measured for various window types and lengths. The simulation results demonstrate that the proposed algorithm achieves significant improvement in terms of BER and PAPR reduction performance while maintaining similar spectrum performance compared to the conventional peak windowing scheme.

Multi-core processors have been attracting a great deal of attention. In the domain of signal processing for communications, the current trends toward rapidly evolving standards and formats, and toward algorithms adaptive to dynamic factors in the environment, require programmable solutions that possess both algorithm flexibility and low implementation complexity. Reconfigurable architectures have demonstrated better tradeoffs between algorithm flexibility, implementation complexity, and energy efficiency. This paper presents a reconfigurable homogeneous memory-based FFT processor (MBFFT) architecture integrated in a single chip to provide hybrid SISO/MIMO OFDM wireless communication systems. For example, a reconfigurable MBFFT processor with eight processing elements (PEs) can be configured for one DVB-T/H with N=8192 and two 802.11n with N=128. The reconfigurable processors can perfectly fit the applications of Software Defined Radio (SDR) which requires more hardware flexibility.

Quadratic congruence code (QCC)-based frequency-hopping and time-spreading (FH/TS) optical orthogonal codes (OOCs), and the corresponding expanded cardinality were recently studied to improve data throughput and code capacity. In this paper, we propose a new FH/TS two-dimensional (2-D) code using the QCC and the cubic congruence code (CCC), named as the QCC/CCC 2-D code. Additionally the expanded CCC-based 2D codes are also considered. In contrast to the conventional QCC-based 1-D and QCC-based FH/TS 2-D optical codes, our analysis indicates that the code capacity of the CCC-based 1-D and CCC-based FH/TS 2-D codes can be improved with the same code weight and length, respectively.

Orthogonal frequency division multiplexing has emerged as a promising air interface scheme for wireless broadband communications. For OFDM systems, frame synchronization has received much attention in the literature, though simple correlators are still widely used in real systems. In this letter, we present the analytical expression of the optimal frame synchronizer for OFDM systems. Frame synchronization is posed as a maximum a posteriori probability estimation. We show that the resulting frame synchronizer consists of a correlation term and a correction term. The correction term accounts for the random data surrounding a synchronization word. Numerical results show the performance gain of the proposed frame synchronizer over a correlation scheme.

This paper presents an improved version of multi-stage threshold decoding with a difference register (MTD-DR) for self-orthogonal convolutional codes (SOCCs). An approximate lower bound on the bit error rate (BER) with the maximum likelihood (ML) decoding is also given. MTD-DR is shown to achieve an approximate lower bound of ML decoding performance at the higher Eb/N0. The code with larger minimum Hamming distance reduces the BER in error floor, but the BER in waterfall shifts to the higher Eb/N0. This paper gives a decoding scheme that improves the BER in both directions, waterfall and error floor. In the waterfall region, a 2-step decoding (2SD) improves the coding gain of 0.40 dB for shorter codes (code length 4200) and of 0.55 dB for longer codes (code length 80000) compared to the conventional MTD-DR. The 2-step decoding that serially concatenates the parity check (PC) decoding improves the BER in the error floor region. This paper gives an effective use of PC decoding, that further makes the BER 1/8 times compared to the ordinary use of PC decoding in the error floor region. Therefore, the 2SD with effective use of parity check decoding improves the BER in the waterfall and the error floor regions simultaneously.

Quantization is an important operation in digital communications systems. It not only introduces quantization noise but also changes the statistical properties of the quantized signal. Furthermore, quantization noise cannot be always considered as an additive source of Gaussian noise as it depends on the input signal probability density function. In orthogonal-frequency-division-multiplexing transmission the signal undergoes different operations which change its statistical properties. In this paper we analyze the statistical transformations of the signal from the transmitter to the receiver and determine how these effect the quantization. The discussed process considers the transceiver parameters and the channel properties to model the quantization noise. Simulation results show that the model agrees well with the simulated transmissions. The effect of system and channel properties on the quantization noise and its effect on bit-error-rate are shown. This enables the design of a quantizer with an optimal resolution for the required performance metrics.

EIRP measurement in the direction of maximum radiation has not always been valid to estimate the radiated power from radio equipments integrated with antennas, for example, integrated radiator with antennas shaped like the notebook-sized PC. Therefore, it is recommended that total radiated power (TRP) from equipment under test (EUT) should be estimated by integrating measured EIRPs on the whole surface of the unit sphere. In this paper, a conventional and some novel sampling methods for the TRP estimation, which were proposed to reduce the number of measurement points, are examined by using a measured EIRP data set and compared with each other. For a simulated radio equipment shaped like a notebook-sized PC, it is found that the equi-area and generalized spiral points methods are superior to the equi-angle method in terms of reducing the number of the measurement points and orthogonal three planes method is another candidate in terms of saving measurement time unless the pattern radiated from EUT is not so complicated.

A resource allocation scheme for multi-access MIMO-OFDM systems in uplink was developed to improve power and spectrum efficiency in the frequency and the space domains [1]. The scheme requires a multi-user detector in the receiver and assumes identical spatial crosscorrelation across all subcarriers for any pair of spatially separable users. However, the multi-user detection device may not exist in the receiver and the identical spatial crosscorrelation assumption may not be valid in some operational scenarios. The paper develops a scheme to remedy these problems for multi-access MIMO-OFDM systems without using multi-user detection techniques and the assumption. The proposed scheme aims at minimizing the total user transmit power while satisfying the required data rate, the maximum transmit power constraint, and the bit error rate of each user. The simulation results are presented to demonstrate the efficacy of the proposed algorithm.

In this paper, two constructions of mutually orthogonal zero correlation zone polyphase sequence sets are presented. The first one is based on DFT matrices and interleaving iteration. After each recursive step, the period of sequence and the length of zero-correlation zone are two times larger than that in the last step. The second method, based on DFT matrices and orthogonal matrices, can generate numbers of mutually orthogonal optimal ZCZ sequence sets whose parameters reach the theoretical bounds by using interleaving and shifting techniques. As a result, the algorithms proposed can provide more sequences for the QS-CDMA (quasi-synchronous CDMA) systems.

This letter introduces a blind minimum interference symbol synchronization for orthogonal frequency-division multiplexing (OFDM) systems based on the cyclic prefix (CP). The basic idea of our contribution is to obtain an estimate of the channel-tap powers from the correlation characteristics of the CP. Based on the estimate of the channel-tap powers, a minimum interference metric is proposed. The proposed algorithm has low complexity and can be used to cope with long inter-symbol-interference (ISI) channels with length up to twice the CP length.

In this letter, we propose a set of Space-Time Block Codes (STBC) equipped with 4 transmit antennas to transmit one additional information bit achieving rate-9/8. To maintain full rank property of the coding gain matrix, one new orthogonal STBC code with full rate is proposed in this letter. Simulation results show that this method achieves good bit error rate (BER) performance with a small gap compared to that of the rate-1 case and throughput in the high SNR region.

A differential cross-correlation cell ID identification algorithm is proposed for IEEE 802.16e OFDMA cellular system. The cell ID represents the number of the preamble selected by the base station in downlink mode. First, we construct the downlink (DL) preamble structure and signal model with carrier frequency offset (CFO) and channel effects. Next, in order to achieve the initial synchronization, a differential receiver with cross correlation for all preamble patterns is proposed to search for cell ID. Simulation results confirm that the proposed structure is suitable for ITU fading channels and outperforms the conventional cell search system.

In this paper, we design a practical time-reversal quasi-orthogonal space-time block code (TR-QO-STBC) system for broadband multi-input multi-output (MIMO) communications. We first modify the TR-QO-STBC encoding structure so that the interference between the transmitted blocks can be completely removed by linear processing. Two low complex decision-feedback equalization (DFE) schemes are then proposed. One is built from the frequency-domain decision-feedback equalization (FD-DFE). The derived bi-directive FD-DFE (BiD-FD-DFE) cancels the interference among the successive symbols along the time axis. The other one is the enhanced V-BLAST, which cancels the interference between the real and imaginary parts of the spectral components. They have distinct performance characteristics due to the different interference-cancellation strategies. The underlying orthogonal and symmetric characters of TR-QO-STBC are exploited to reduce the computational complexity. Computer simulations confirm that the proposed equalizers can achieve better performance than the existing schemes.

In UWB systems, data symbols are transmitted and received continuously. The Fast Fourier Transform (FFT) processor must be able to seamlessly process input/output data. This paper presents the design and implementation of a continuous data flow parallel memory-based FFT (CF-PMBFFT) processor without the use of input buffer for pre-loading the input data. The processor realizes a memory space of two N-words and multiple processing elements (PEs) to achieve the seamless data flow and meet the design requirement. The circuit has been fabricated in TSMC 0.18 µm 1P6M CMOS process with the supply voltage of 1.8 V. Measurement results of the test chip shows that the developed CF-PMBFFT processor takes a core area of 1.97 mm2 with a power consumption of 62.12 mW for a throughput rate of 528 MS/s.

The logic mapping problem and the problem of finding a largest sub-crossbar with no defects in a nano-crossbar with nonprogrammable-crosspoint defects and disconnected-wire defects are known to be NP-hard. This paper shows that for nano-crossbars with only disconnected-wire defects, the former remains NP-hard, while the latter can be solved in polynomial time.

Advanced Evolved Universal Terrestrial Radio Access (Advanced E-UTRA), called LTE-Advanced, has been standardized in the 3rd Generation Partnership Project (3GPP) as a candidate for IMT-Advanced. LTE-Advanced supports spatial orthogonal-resource transmit diversity (SORTD) [1],[2] for ACK/NACK signals and scheduling requests (SRs), which are used to control downlink hybrid automatic repeat requests (HARQs) and manage uplink radio resources based on uplink data traffic, respectively. Both ACK/NACK signals and SRs are carried via a physical uplink control channel (PUCCH) [3], and a common PUCCH format is used for both ACK/NACK signals and SRs. If SORTD is used, the base station assigns mutually orthogonal resources to each antenna included in the user equipment (UE) for ACK/NACK signals and SRs; hence, the number of required resources increases with the number of transmitting antennas in the UE. In this paper, we study the resource reduction method for ACK/NACK signal and SR in case of SORTD using the concept of common resource. In addition, we investigate a phase rotation scheme for common resources to improve the SR detection performance.

In OFDM systems, in-phase and quadrature (I/Q) imbalances generated in the analog front-end introduce inter-channel interference and, consequently, error performance degradation. This letter provides an exact expression involving the two-dimensional (2-D) Gaussian Q-function for the error probability of an arbitrary 2-D modulated OFDM signal with I/Q imbalances. The effects of I/Q imbalances on the distribution of an AWGN and the error performance are analyzed.