In this letter, the tradeoff between symbol rate and diversity gain of Space-Time Block Codes (STBCs) with linear receivers is considered. It is known that Group Orthogonal-Toeplitz Codes (GOTCs) can achieve a good tradeoff with linear receivers. However, the symbol rate of GOTCs is limited to that of the base Orthogonal Space-Time Block Codes (OSTBCs). We propose to simply change the GOTC base codes from OSTBCs to Quasi-Orthogonal Space-Time Block Codes (Q-OSTBCs). Q-OSTBCs can improve the symbol rate of GOTCs at the expense of diversity gain. Simulation results show that Q-OSTBC based GOTCs can improve the tradeoff between symbol rate and diversity gain over that of the original GOTCs.

In wireless sensor networks, unbalanced energy consumption and transmission collisions are two inherent problems and can significantly reduce network lifetime. This letter proposes an unequal clustering and TDMA-like scheduling mechanism (UCTSM) based on a gradient sinking model in wireless sensor networks. It integrates unequal clustering and TDMA-like transmission scheduling to balance the energy consumption among cluster heads and reduce transmission collisions. Simulation results show that UCTSM balances the energy consumption among the cluster heads, saves nodes' energy and so improves the network lifetime.

Orthogonal frequency division multiplexing (OFDM) has great advantages such as high spectrum efficiency and robustness against multipath fading. In order to enhance the advantages, an Hermite-symmetric subcarrier coding for OFDM, which is used for transmission systems like the asymmetric digital subscriber line (ADSL) and multiband OFDM in ultra-wideband (UWB) communications, is very attractive. The subcarrier coding can force the imaginary part of the OFDM signal to be zero, then another data sequence can be simultaneously transmitted in the quadrature channel. In order to theoretically verify the effectiveness of the Hermite-symmetric subcarrier coding in wireless OFDM (HC-OFDM) systems, we derive closed-form equations for bit error rate (BER) and throughput over fading channels. Our analytical results can theoretically indicate that the HC-OFDM systems achieve the improvement of the performances owing to the effect of the subcarrier coding.

We propose three operation modes, namely, DCF uplink, Downlink, and CTS uplink modes to solve the unfairness problem between uplink and downlink as well as improve the performance of delay and throughput. The proposed scheme only requires modifying AP's functionalities without any changes of STAs, and is fully backward compatible to the legacy DCF. Its analytical result is validated against simulation and performance evaluation shows the proposed scheme is superior to the traditional IEEE 802.11 WLAN.

A parameterization of perfect sequences over composition algebras over the real number field is presented. According to the proposed parameterization theorem, a perfect sequence can be represented as a sum of trigonometric functions and points on a unit sphere of the algebra. Because of the non-commutativity of the multiplication, there are two definitions of perfect sequences, but the equivalence of the definitions is easily shown using the theorem. A composition sequence of sequences is introduced. Despite the non-associativity, the proposed theorem reveals that the composition sequence from perfect sequences is perfect.

This study presents an adaptive quantization index modulation scheme applicable on a small audio segment, which in turn allows the watermarking technique to withstand time-shifting and cropping attacks. The exploitation of auditory masking further ensures the robustness and imperceptibility of the embedded watermark. Experimental results confirmed the efficacy of this scheme against common signal processing attacks.

In this letter, we present a method for improving the front-to-back ratio (FBR) of a broadcast antenna. The digitalization of terrestrial TV demands more efficient channel usage due to the reduction in TV bands after the switch-over. Thus, we designed an antenna with an FBR improved over -45 dB as compared to the -20 to -25 dB FBR range of existing antennas. We show experimentally that this antenna satisfies the required performance.

This paper presents comprehensive comparisons based on the block error rate (BLER) of open-loop (OL) transmit diversity schemes considering a cubic metric (CM) for single-carrier (SC)-Frequency Division Multiple Access (FDMA) using discrete Fourier transform (DFT)-precoded OFDMA in uplink frequency-selective fading channels. The OL transmit diversity schemes assumed in the paper are space-time block code (STBC), space-frequency block code (SFBC), single-carrier (SC) - SFBC, cyclic delay diversity (CDD), and frequency switched transmit diversity (FSTD) for two antennas and a combination of STBC, SFBC, SC-SFBC and selection transmit diversity including time switched transmit diversity (TSTD) or FSTD for four antennas. We derive the most appropriate OL transmit diversity scheme for SC-FDMA using a frequency domain equalizer (FDE) with QPSK and 16QAM modulations and with various channel coding rates employing turbo coding. We investigate the best OL transmit diversity scheme under various propagation channel conditions including the fading maximum Doppler frequency and root mean square (r.m.s.) delay spread, and the fading correlation between transmitter/receiver antennas.

The interference rejection combining (IRC) receiver, which can suppress inter-cell interference, is effective in improving the cell-edge user throughput. The IRC receiver is typically based on the minimum mean square error (MMSE) criteria, and requires a covariance matrix including the interference signals, in addition to a channel matrix from the serving cell. Therefore, in order to clarify the gain from the IRC receiver, the actual estimation error of these matrices should be taken into account. In a system performance evaluation, the link performance modeling of the IRC receiver, i.e., the output signal-to-interference-plus-noise power ratio (SINR) after IRC reception including the estimation errors, is very important in evaluating the actual performance of the IRC receiver in system level simulations. This is because these errors affect the suppression of the interference signals for the IRC receiver. Therefore, this paper investigates and proposes IRC receiver modeling schemes for the covariance matrix and channel estimation errors. As the modeling scheme for the covariance matrix, we propose a scheme that averages the conventional approximation using the complex Wishart distribution in the frequency domain to address issues that arise in a frequency selective fading channel. Furthermore, we propose a modeling scheme for the channel estimation error according to the ideal channel response of all cells and a channel estimation filter to address channel fading fluctuations. The results of simulations assuming the LTE/LTE-Advanced downlink with two transmitter and receiver antenna branches show that the proposed modeling scheme for the covariance matrix estimation error accurately approximates the performance of a realistic IRC receiver, which estimates the covariance matrix and channel matrix of the serving cell based on the demodulation reference signal (DM-RS), even in a frequency selective fading channel. The results also show that the proposed modeling scheme for the channel estimation error is a robust scheme in terms of the r.m.s. delay spread of a channel model compared to the scheme using the mean square error (MSE) statistic of the estimated channel coefficients based on a channel estimation filter.

Characterization of peer-to-peer (P2P) traffic is an essential step to develop workload models towards capacity planning and cyber-threat countermeasure over P2P networks. In this paper, we present a classification scheme for characterizing P2P file-sharing hosts based on transport layer statistical features. The proposed scheme is accessed on a virtualized environment that simulates a P2P-friendly cloud system. The system shows high accuracy in differentiating P2P file-sharing hosts from ordinary hosts. Its tunability regarding monitoring cost, system response time, and prediction accuracy is demonstrated by a series of experiments. Further study on feature selection is pursued to identify the most essential discriminators that contribute most to the classification. Experimental results show that an equally accurate system could be obtained using only 3 out of the 18 defined discriminators, which further reduces the monitoring cost and enhances the adaptability of the system.

Two-dimensional (2-D) codes for optical code-division multiple access (O-CDMA) systems can increase the number of subscribers and simultaneous users as compared to one-dimensional time-spreading codes. Multiple-wavelength optical orthogonal code (MWOOC), which is one of the 2-D codes, uses prime sequences as a wavelength-hopping code and an optical orthogonal code (OOC) as a time-spreading code. MWOOCs have some advantages over other 2-D codes especially in high bit-rate O-CDMA systems. The only drawback of MWOOC is that the performance degrades significantly when the number of wavelengths is not prime. Recently a generalized class of modified prime sequence codes (MPSCs), which includes the class of original MPSCs as its subclass, was presented. An important property of generalized MPSCs is that the codes can be constructed over not only prime fields but also extension fields. It has been shown that the correlation property of generalized MPSCs is the same as that of the original MPSCs. This paper investigates MWOOC with generalized prime sequences, which can be obtained in the process of generating the generalized MPSCs, as a wavelength-hopping code. Use of the generalized prime sequences can solve the nonprime problem of MWOOCs. The average error probability of the proposed MWOOCs is formulated theoretically and numerical results are compared with that of the original schemes. It is shown that nonprime numbers, such as 2m, 3m and 5m, can be also taken as the number of wavelengths without degrading the system performance in the proposed systems.

Bipolar complementary sequence pairs of Types II and III are defined, enumerated for n ≤ 28, and classified. Type-II pairs are shown to exist only at lengths 2m, and necessary conditions for Type-III pairs lead to a non-existence conjecture regarding their length.

In time-varying frequency selective channels, to obtain high-rate joint time-frequency diversity, linear dispersion coded orthogonal frequency division multiplexing (LDC-OFDM), has recently been proposed. Compared with OFDM systems, single-carrier systems may retain the advantages of lower PAPR and lower sensitivity to carrier frequency offset (CFO) effects, which motivates this paper to investigate how to achieve joint frequency and time diversity for high-rate single-carrier block transmission systems. Two systems are proposed: linear dispersion coded cyclic-prefix single-carrier modulation (LDC-CP-SCM) and linear dispersion coded zero-padded single-carrier modulation (LDC-ZP-SCM) across either multiple CP-SCM or ZP-SCM blocks, respectively. LDC-SCM may use a layered two-stage LDC decoding with lower complexity. This paper analyzes the diversity properties of LDC-CP-SCM, and provides a sufficient condition for LDC-CP-SCM to maximize all available joint frequency and time diversity gain and coding gain. This paper shows that LDC-ZP-SCM may be effectively equipped with low-complexity minimum mean-squared error (MMSE) equalizers. A lower complexity scheme, linear transformation coded SCM (LTC-SCM), is also proposed with good diversity performance.

The present paper introduces a new approach to the construction of a sequence set with a zero-correlation zone (ZCZ), which is referred to as a ZCZ sequence set. The proposed sequence construction generates a ZCZ sequence set from a ZCZ sequence set. The proposed method can generate an almost optimal ZCZ sequence set, the member size of which approaches the theoretical bound, when an almost optimal ZCZ sequence is used for the sequence construction. The proposed sequence set consists of NO subsets, where a ZCZ sequence set Z(LO, NO, ZO is used in sequence construction. The correlation function of the sequences of a pair of different subsets, referred to as the inter-subset correlation function, has a ZCZ with a width that is about times that of the correlation function of sequences of the same subset (intra-subset correlation function) for integers Λ ≥ 1, T, and m ≥ 0. Wide inter-subset zero-correlation enables improved performance during application of the proposed sequence set.

For advanced mobile communication systems that adopt orthogonal frequency-division multiple access (OFDMA) technologies, intercarrier interference (ICI) significantly degrades performance when mobility is high. Standard specifications and concerns about complexity demand low-cost methods with deployment readiness and decent performance. In this paper, novel zero forcing (ZF) and minimum mean-square error (MMSE) equalizers based on per-subcarrier adaptive (PSA) processing and perturbation-based (PB) approximation are introduced. The proposed equalizers strike a good balance between implementation cost and performance; therefore they are especially suitable for OFDMA downlink receivers. Theoretical analysis and simulations are provided to verify our claims.

Multicarrier communications including orthogonal frequency-division multiplexing (OFDM) is a technique which has been adopted for various wireless applications. However, a major drawback to the widespread acceptance of OFDM is the high peak-to-mean envelope power ratio (PMEPR) of uncoded OFDM signals. Finding methods for construction of sequences with low PMEPR is an active research area. In this paper, by employing some new shortened and extended Golay complementary pairs as the seeds, we enlarge the family size of near-complementary sequences given by Yu and Gong. We also show that the new set of sequences we obtained is just a reversal of the original set. Numerical results show that the enlarged family size is almost twice of the original one. Besides, the Hamming distances of the binary near-complementary sequences are also analyzed.

In block transmissions, inter-block interference (IBI) due to delayed waves exceeding a cyclic prefix severely limits the performance. To suppress IBI in downlink MC-CDMA systems, this paper proposes a novel channel shortening method using a time-domain equalizer. The proposed method minimizes a cost function related to equalizer output autocorrelations without the transmission of training symbols. We prove that the method can shorten a channel and suppress IBI completely. Simulation results show that the proposed method can significantly suppress IBI using relatively less number of received blocks than a conventional method when the number of users is moderate.

A scheme that modulates the training sequence is proposed to support two-layer data streams in the time domain synchronous orthogonal frequency division multiplex (TDS-OFDM) systems. A theoretical analysis and computer simulation show that the proposed scheme works well and that the two layer data streams are compatible with each other.

In this paper, we analyze the existing results to derive the cross-correlation distributions of p-ary m-sequences and their decimated sequences for an odd prime p and various decimations d. Based on the previously known results, a methodology to obtain the distribution of their cross-correlation values is also formulated.

In this paper, we propose a normalization method dividing the gradient vector by the sum of the diagonal and two adjoining elements of the matrix expressing the correlation between the components of the discrete Fourier transform (DFT) of the reference signal used for the identification of unknown system. The proposed method can thereby improve the estimation speed of coefficients of adaptive filter.