Orthogonal Complementary Codes Research Articles

Rail fracture monitoring based on ultrasonic-guided wave technology with multivariate coded excitation

Steel lay the basis of railroad train traffic. Rail fracture is the most serious injury to the rail, which should be monitored in time. The conventional mono-pulse exciting ultrasonic guide wave (UGW) has low energy, the conventional Barker code has limited coding sequence length and the orthogonal complementary Golay code has the problem of low monitoring efficiency. This study proposes multivariate coded excitation (MCE) to excite UGW to monitor rail fracture, and the feasibility of coding and decoding the method is theoretically derived and verified. Ideally, the MCE generated based on the 3-bit Barker code (B3: 1,1, −1) and 4-bit orthogonal complementary Golay code (GA4: 1,1,1, −1; GB4: 1,1, −1,1) is calculated to have a main-lobe power level (MPL) gain of 8.1020 dB, which is significantly higher than the MPL of Barker and Golay codes. For the proposed method, finite element modeling simulation and experimental study are carried out respectively. Analyze and process the data, and calculate the gain of the difference in amplitude (DIA) between the amplitude of echo caused by rail fracture and the amplitude in the healthy rail. The gain of the DIA of the echoes in the MCE is above 50 dB (experimental data, the value of simulation data is 5 dB) under different degrees of rail fracture, while the gain of the DIA of the echoes caused by the other three excitation methods is below 40 dB (experimental data, the value of simulation data is 1 dB). Simulation and experimental results show that the MCE makes up for the shortcomings of the conventional Barker code and Golay code, improves the excitation energy of the monitoring system, and the high gain of the DIA of the echoes is more conducive to the identification of rail fracture damage.

Constructions of Asymptotically Optimal Aperiodic Quasi-Complementary Sequence Sets

Mutually orthogonal complementary codes have found many practical applications in wireless communications owing to their perfect correlation properties. However, the set size of a mutually orthogonal complementary code set (MOCCS) is upper bounded by the number of constituent sequences in each complementary code. As a result, the number of users in the communication system is limited. To overcome this limitation, quasi-complementary sequence sets (QCSSs) were proposed, which include low correlation zone complementary sequence sets (LCZ-CSSs) and low correlation complementary sequence sets (LC-CSSs). In this paper, aperiodic quasi-complementary sequences are our main interest. Constructions of aperiodic LC-CSSs and aperiodic LCZ-CSSs over the complex roots of unity are proposed. With these constructions, asymptotically optimal aperiodic QCSSs can be obtained.

Omnidirectional Quasi-Orthogonal Space–Time Block Coded Massive MIMO Systems

Common signals in public channels of cellular systems are usually transmitted omnidirectionally from the base station (BS). In recent years, both discrete and consecutive omnidirectional space–time block codings (STBC) have been proposed for massive multiple-input multiple-output (MIMO) systems with a uniform linear array (ULA) configuration to ensure cell-wide coverage. In these systems, constant received signal power at discrete angles, or constant received signal sum power in a few consecutive time slots at any angle is achieved. In addition, an equal-power transmission per antenna and a full spatial diversity can be achieved as well. In this letter, by utilizing the property of orthogonal complementary codes (OCCs), a new consecutive omnidirectional quasi-orthogonal STBC (QOSTBC) design is proposed, in which constant received sum power at any angle can be realized with the equal-power transmission per antenna through one STBC transmission, and a higher diversity order of four can be achieved. Moreover, the proposed design can be further extended to the uniform planar array (UPA) configuration with the two-dimensional OCCs.

OCC-Selection-Based High-Efficient UWB Spatial Modulation System Over a Multipath Fading Channel

In this paper, an orthogonal complementary code (OCC)-selection-based high-efficient ultrawideband (UWB) spatial modulation (SM) system has been proposed to achieve higher transmission rate and better system performance. The OCC is employed to spread the spectrum, carry extra information bits, and alleviate the multipath interference simultaneously. Meanwhile, the SM technique is adopted to further increase the system bit rate and overcome the synchronization and interference issues of a multiantenna system. In the proposed UWB SM system, the information bits are conveyed through three ways: direct bipolar pulse amplitude modulation, indirect spread spectrum code selection, and transmit antenna selection. To further enhance the system performance over a multipath fading channel, the selective Rake receiver and maximum ratio combining detection are utilized. A closed-form expression of the system bit error rate is derived through the moment-generating function. Numerical results are provided to verify the theoretical analysis and show the efficiency and performance improvement of the proposed OCC-selection-based UWB SM system.

Omnidirectional Space–Time Block Coding Design for Three-Dimensional Massive MIMO Systems

Common signals in public channels of cellular systems are usually transmitted omnidirectionally by the base station (BS) to ensure cell-wide coverage. In this paper, two categories of omnidirectional space-time block codes (STBCs) are proposed to broadcast the common information omnidirectionally in three-dimensional (3D) massive multiple-input multiple-output (MIMO) systems. By utilizing Zadoff-Chu sequences, we propose a discrete omnidirectional STBC, through which constant received signal power at discrete angles is achieved while guaranteeing equal-power transmission per antenna. Then, by utilizing two-dimensional orthogonal complementary codes (2D-OCCs), we also propose a consecutive omnidirectional STBC, which is insensitive to the number of BS antennas, and can realize constant received sum power at any angle through one STBC transmission. Besides, through theoretic analyses, we also demonstrate that all the proposed STBC designs can achieve full diversity order. Simulation results verify the effectiveness of the proposed omnidirectional STBC designs.

Beam coding with orthogonal complementary Golay codes for signal-to-noise ratio improvement in ultrasound mammography

In this paper, the experimental results of using Golay coded signals at 7.5 MHz to detect breast microcalcifications of 50 μm size is presented. For improving the success on detecting the microcalcifications, orthogonal Golay complementary sequences up to 40 chips having cross correlation for minimum interference are used as coded signals and they are compared to tone burst pulse of equal energy in terms of resolution under weak signal conditions. The measurements are conducted using an experimental ultrasound research scanner, DiPhAS having 256 channels, a phased array transducer with 7.5 MHz center frequency, and the results obtained through experiments are validated by Field-II simulation software. In addition, to investigate the superiority of coded signals in terms of resolution, multipurpose tissue equivalent phantom (Model 84-317) containing series of monofilament nylon targets, 240 μm in diameter, and cyst-like objects with attenuation of 0.5 dB/(MHz*cm) is used in the experiments. We obtained ultrasound images of monofilament nylon targets and cyst-like objects for the evaluation of resolution. Experimental results show that it is possible to differentiate closely positioned small targets with increased success by using coded excitation in very weak signal conditions.In this paper, the experimental results of using Golay coded signals at 7.5 MHz to detect breast microcalcifications of 50 μm size is presented. For improving the success on detecting the microcalcifications, orthogonal Golay complementary sequences up to 40 chips having cross correlation for minimum interference are used as coded signals and they are compared to tone burst pulse of equal energy in terms of resolution under weak signal conditions. The measurements are conducted using an experimental ultrasound research scanner, DiPhAS having 256 channels, a phased array transducer with 7.5 MHz center frequency, and the results obtained through experiments are validated by Field-II simulation software. In addition, to investigate the superiority of coded signals in terms of resolution, multipurpose tissue equivalent phantom (Model 84-317) containing series of monofilament nylon targets, 240 μm in diameter, and cyst-like objects with attenuation of 0.5 dB/(MHz*cm) is used in the experiments. We obtained ult...

MIMO Radar Waveforms Using Orthogonal Complementary Codes with Doppler-Offset

MIMO Radar Waveforms Using Orthogonal Complementary Codes with Doppler-Offset

Modified Chirp Waveforms-Based OCC-UWB System With Multiple Interferences Suppression

To improve the performance of the ultra-wideband (UWB) system against multiple interferences existed in wireless personal area network (WPAN), such as narrowband interference (NBI), multiple-access interference (MAI), and multipath interference (MI), we present an orthogonal complementary code (OCC)-based UWB system with modified chirp waveforms. Considering the time–frequency characteristics of the chirp functions and the principle of NBI suppression, we first propose the modified linear and nonlinear chirp function-based flexible UWB pulses to suppress the multiple NBIs. Furthermore, with the implementation of OCC spread modulation, the modified chirp waveform-based UWB system is presented to effectively alleviate the influence of the MAI and MI. Simulation results and analysis validate the efficiency of the modified chirp pulse-based OCC-UWB system in the suppression of NBIs, MAI, and MI.

A Direct Construction of Inter-Group Complementary Code Set

Complete complementary codes (CCCs) is a collection of mutually orthogonal complementary codes and Inter-group complementary (IGC) code set consists of multiple disjoint groups of 2-D codes. IGC code set has large set size than CCC and both can be applicable in multicarrier code-division multiple access. The aperiodic autocorrelation function sidelobes of any IGC code is zero for all time shifts inside the zero-correlation zone (ZCZ). The aperiodic crosscorrelation functions (ACCF) of any two distinct IGC codes are zero everywhere if they are from two different groups; when they are drawn from the same group, their ACCFs are zero inside the ZCZ width. This paper presents a direct construction of the IGC code set, which can support interference-free code-division multiplexing using second-order generalized Boolean functions. We relate our construction with a graph where the ZCZ width depends on the number of isolated vertices presented in a graph after the deletion of some vertices. Moreover, our construction is capable of generating the IGC code set with more flexible parameters.

Multiband chirp OCC‐UWB system design for suppression of multiple narrowband interferences

AbstractTo improve the coexistence between ultrawideband (UWB) technology–based wireless personal area networks and other narrowband systems and efficiently suppress the multiple narrowband interferences (NBIs) and the multiuser interference (MUI) in UWB systems, we propose a multiband orthogonal complementary code–based UWB (OCC‐UWB) system design in this paper, which utilizes the simple time‐frequency relationship of the chirp waveforms. The system design is implemented in 2 ways, named the equant multiband scheme and the nonequant multiband scheme. The 2 implementation schemes can improve the spectrum utilization of UWB systems and have different principles of NBI suppression. The equant scheme adopts the nonlinear chirp waveforms to suppress multiple NBIs in the subbands with NBIs. In contrast, the nonequant scheme adopts the spectrum elusion method based on the division of the frequency band to exclude the NBIs' frequency bands. Combining the chirp UWB pulse design with the orthogonal complementary code spread modulation, we finally present the multiband chirp OCC‐UWB system to suppress the MUI and the multipath interference simultaneously. Simulation results and theoretical analysis show that the proposed multiband chirp OCC‐UWB system improves the system performance efficiently in the conditions of multiple NBIs, MUI, and multipath interference and increases the data transmission rate and the spectrum utilization simultaneously.

Performance of CHMA System Using Orthogonal Complementary Codes under Diversity Incorporated Fading Channels

Code-Hopping Multiple Access (CHMA) has been an emerging Multiple Access (MA) technology which offers excellent performance in multipath fading channels with Orthogonal Complementary Codes (OCC). Orthogonality among users is not preserved in multipath channel conditions using the existing orthogonal and semi-orthogonal codes. Further, Multiple Access Interference (MAI) and Multipath Interference (MPI) destroy orthogonality of the code set which in turn increases the error rate during the detection process. An OCC set possesses both ideal auto-correlation and ideal cross-correlation properties for any two codes in the same set. Here, we employ OCC for spreading and prove that the performance of OCC is superior to those of Gold codes in multipath channels where orthogonality does not hold. The error probability expressions for Rayleigh and Nakagami-m fading channels using Maximal Ratio Combining (MRC) are derived for CHMA system using OCCs. We then evaluate the system performance using the proposed technique and show that the new scheme is much better compared to traditional CHMA schemes.

I/Q Column-Wise Complementary Codes for Interference-Resistant CDMA Communication Systems

Motivated by growing demand for high-speed wireless communications, we proposed to implement code division multiple access systems based on orthogonal complementary codes (OCC-CDMA). While an OCC-CDMA system indeed offers ideal correlation properties, its capacity is strictly constrained by the number of element codes each user may use. In this paper, we suggest to use in-phase/quadrature (I/Q) column-wise complementary (IQCC) codes to implement a CDMA system to support $2M$ users, where $M$ stands for the number of element codes in a flock of IQCC codes assigned to a user. The IQCC codes were designed to fit quadrature phase-shift keying modulation, where odd and even chips can be transmitted via I and Q carriers. We analyze correlation properties of the IQCC codes and introduce a CDMA system design based on the codes. The analytical results show that out-of-phase autocorrelation and cross-correlation functions are zero for any relative time shifts. Thus, a CDMA system implemented by the IQCC codes has an inherent capability to mitigate multiple access interference and multipath interference.

Decode-and-forward relaying based on orthogonalcomplementary codes

In this note, we propose a full-duplex decode-and-forward cooperative diversity scheme based on code division with orthogonal complementary codes. We consider a simple case in which a single user is assisted by a single relay to achieve cooperative diversity. When the cooperation is full-duplex, the operational delay of the relay makes the channel asynchronous and this may cause multiple-access interference (MAI) between the user and relay. The orthogonal complementary codes have perfect autocorrelation and cross-correlation properties that provide MAI-free operation in asynchronous channels. In the proposed scheme, the user and relay terminals spread their messages with complementary codes and the spread messages can reach the destination without interfering with each other. The numerical results reveal that the proposed scheme reaches the same bit-error-rate performance in both synchronous and asynchronous channels. The results are also compared with the conventional orthogonal code sets, such as Hadamard sets, which fail to provide diversity.

Multiple access interference and multipath interference analysis of orthogonal complementary code‐based ultra‐wideband systems over multipath channels

SUMMARYIn order to alleviate multiple access interference and multipath interference of ultra‐wideband (UWB) system, we propose the orthogonal complementary code (OCC)‐based direct‐sequence UWB system and offset‐stacking (OS)‐UWB system. OCC has perfect partial autocorrelation and cross‐correlation characteristics. With the application of OCC in UWB system, we can obtain better performance in multiple access interference and multipath interference. The proposed OS‐UWB structure can also achieve variable data rate transmission because of its innovative OS spreading technique. Theoretical analysis and simulation results show that the proposed UWB system can achieve excellent performance and outperform the unitary code‐based direct‐sequence UWB system. Copyright © 2013 John Wiley & Sons, Ltd.

A Novel Underlay Cognitive Radio Based on Direct Sequence Complementary Coded CDMA

In this study, we propose a spectrum sharing scheme where secondary-users (SUs) can co-exist at the same frequency band with the primary-users simultaneously. Both primary (PN) and secondary networks (SN) are considered as CDMA based networks with the same set of orthogonal complementary codes. An orthogonal complementary code set possesses both ideal auto-correlation function (ACF) of any code and ideal cross-correlation function for any two codes in the same set. In the proposed scheme, a delay is applied to the transmission of the SN which exploits ideal ACF properties of complementary codes and will not interfere the transmission of the primary user. Numerical results show that the proposed scheme enables SUs to efficiently utilize the PN's licensed spectrum without any harmful interference.

Evolution from symbol‐level space–time coded MIMO to chip‐level space–time coded MIMO: a review

ABSTRACTSpace–time coded multiple‐input multiple‐output (MIMO) technology is an important technique that improves the performance of wireless communication systems significantly without consuming bandwidth resource. This paper first discusses the characteristics and limitations of traditional symbol‐level space–time coding schemes, which work largely on the basis of an assumption that signals are sent to a block‐fading channel. Therefore, the symbol‐level space–time coding schemes rely on symbol‐level signal processing. Taking advantage of orthogonal complementary codes, we propose a novel MIMO scheme, in this paper, based on chip‐level space–time coding that is different from the traditional symbol‐level space–time coding. With the help of space–time–frequency complementary coding and multicarrier modem, the proposed scheme is able to achieve multipath interference‐free and multiuser interference‐free communications with simple a correlator detector. The proposed chip‐level space–time coded MIMO works well even in a fast fading channel in addition to its flexibility to achieve diversity and multiplexing gains simultaneously in varying channel environments. Copyright © 2012 John Wiley & Sons, Ltd.

Code-Hopping Multiple Access Based on Orthogonal Complementary Codes

Code-hopping multiple access (CHMA) is a newly emerging multiple-access technique with the potential to offer high capacity. Unfortunately, orthogonality among user signals in existing CHMA schemes can be preserved only in synchronous channels under an assumption that neither multipath interference (MI) nor multiple-access interference (MAI) exists. Exploiting their ideal orthogonality, we apply orthogonal complementary codes to CHMA systems to overcome problems with existing CHMA schemes. In particular, we will show that the application of orthogonal complementary codes can significantly improve the performance of a CHMA system due to its unique collision-resistant capability. To deal with destructive collisions among spreading codes in CHMA systems, convolutional coding is employed in complementary-coded CHMA systems. The properties and bit error rate (BER) performance of the proposed system are analyzed for both uplink and downlink applications, where the system may simultaneously suffer MI and MAI. Simulation results show that the complementary-coded CHMA with channel coding can provide much higher capacity than complementary-coded code-division multiple access (CDMA) systems in varying operational scenarios.

Quasi-synchronous multicarrier DS-CDMA using Z-Complementary sequences

In this paper, a multicarrier DS-CDMA system which employs Z-Complementary Sequences (ZCS) as spreading code is investigated. The new system can not only eliminate multipath interference and Multiple Access Interference (MAI), but also support flexible number of users compared with system using Orthogonal Complementary (OC) codes. Multicarrier DS-CDMA using OC codes can be regarded as a special case of our proposed system. Zero Correlation Zone (ZCZ) of ZCS can be flexibly adjusted to meet the requirements on the user number and maximum multipath and inter-user delay, in this way, more users can be supported without losing interference-free property. The effectiveness of the proposed system is validated through theoretical analysis and simulation results.

Design of next-generation cdma using orthogonal complementary codes and offset stacked spreading

This article presents an innovative code-division multiple access system architecture that is based on orthogonal complementary spreading codes and time-frequency domain spreading. The architecture has several advantages compared to conventional CDMA systems. Specifically, it offers multiple-access-interference-free operation in AWGN channels, reduces co-channel interference significantly, and has the potential for higher capacity and spectral efficiency than conventional CDMA systems. This is accomplished by using an offset stacked spreading modulation technique followed by quadrature amplitude modulation, which optimizes performance in a fading environment. This new spreading modulation scheme also simplifies the rate matching algorithms relevant for multimedia services and IP-based applications.

A post-compression based ultrasound imaging technique for simultaneous transmit multi-zone focusing

The compression error of post-compression based coded excitation techniques increases with decreasing f-number, which causes the elevation of side-lobe levels. In this paper, a post-compression based coded excitation technique with reduced compression errors through dynamic aperture control is proposed. To improve the near-field resolution with no frame rate reduction, the proposed method performs simultaneous transmit multi-zone focusing using two mutually orthogonal complementary Golay codes. In the proposed method, the two mutually orthogonal sequences of length 16 are simultaneously transmitted toward two different focal depths, which are separately compressed into two short pulses on receive after dynamic focusing is performed. After carrying out the same transmit-receive operation for the same scan line with the complementary set of the orthogonal Golay codes, a single scan line with two transmit foci is obtained.The computer simulation results using a linear array with a center frequency of 7.5 MHz and 60% 6 dB bandwidth show that the range side-lobe level can be suppressed below −50 dB, when f-number is maintained not smaller than 3. The performance of the proposed scheme for a smaller f-number of 2 was also verified through actual experiments using a 3.85 MHz curved linear array with 60% 6 dB bandwidth. Both the simulation and experimental results show that the proposed method provides improved lateral resolution compared to the conventional pre-compressed and post-compression based coded excitation imaging using Golay codes.