Set Of Orthogonal Codes Research Articles

Design of Orthogonal Polyphase Code Set Based on Multi Pulse Joint Processing

Design of Orthogonal Polyphase Code Set Based on Multi Pulse Joint Processing

Hadamard Aperiodic Interval Codes for Parallel-Transmission 2D and 3D Synthetic Aperture Ultrasound Imaging

We present a new set of near orthogonal codes which we call Hadamard Aperiodic Interval (HAPI) codes and demonstrate their utility for parallel multi-transmitter synthetic aperture imaging. The codes are tri-state and sparse. Locations of non-zero bits are based on marks in a sequence of aperiodic intervals, also known as a Golomb ruler. The values of non-zero bits are selected from Hadamard sequences that are mutually orthogonal. This ensures that cross-correlation sidelobe magnitudes between differing codes are bounded by unity while the autocorrelation approaches a delta function with mainlobe-to-sidelobe levels scaling with the number of non-zero bits. We use simulations to demonstrate the potential of the codes for synthetic aperture imaging. A multiplicity of transmitter elements is used to transmit codes simultaneously, with a different code for each element. Echo signals are received from a multiplicity of transducer elements in parallel. Channel data from each receiver element are cross-correlated with respective HAPI codes to estimate the transmit–receive signature associated with each transmitter–receiver pair while minimizing crosstalk. This estimate of the full transmit–receive synthetic aperture dataset is then used to form high-quality images demonstrating image quality and signal-to-noise ratio improvements over multiple flash angle imaging and synthetic aperture imaging methods for linear arrays. We also demonstrate simulated full volume synthetic aperture imaging with random sparse arrays, possible with one extended HAPI code-set transmit event.

Analysis of an algorithm used for finding Unipolar Orthogonal Codes

An Auto-Correlation and Cross-Correlation property of an Orthogonal Code enables the transfer of data with less interference. With more Orthogonal Codes, an Optical Fiber Communication channel can support a large number of users efficiently and reliably with high bandwidth. This paper analyses an algorithm used for finding Unipolar Orthogonal Codes using four major parameters (n, w, λa, and λc) where n is the length of a binary string, w is the weight of the string n (number of one’s in the string), λa is the Auto-Correlation, and λc is the Cross-Correlation. These four parameters jointly with the Johnson Bound (JA) condition are used in the algorithm. The paper illustrates the analysis of a possible number of Orthogonal Code Sets calculated using Orthogonal Codes generated from a software code that is based on the algorithm in consideration. The data analysis is carried out and the findings are summarized.

A Novel Modulation and Multiplexing Technology for Reducing Out-of-Band Leakage Based on Multicarrier Schemes

In this paper, a novel modulation and multiplexing technology for reducing out-of-band leakage is proposed for multicarrier schemes based on CP-OFDM. The proposed method is to spread data of N layers with N selected spreading codes, then multiplex them into a data sequence and transmit it on 2K subcarriers. The N spreading codes, which can suppress out-of-band leakage, are selected out from a complete set of mutual orthogonal spreading codes. The simulation results show that the data modulation and multiplexing technology effectively reduces interference with neighboring frequency bands or adjacent sub-bands for different numerologies and so significantly improves spectrum efficiency

Physical Layer Security for Multiple-Input Multiple-Output Systems by Alternating Orthogonal Space-Time Block Codes

Algorithms are provided to build a large set of unique complex-valued orthogonal space-time block codes (STBCs) from a known or standard STBC. A physical layer security (PLS) scheme is proposed to take advantage of this set by alternating the STBC in use over a multiple-input single-output (MISO) or multiple-input multiple-output (MIMO) communications link between base station (BS) and user equipment (UE). A practical procedure is proposed and demonstrated to build individual STBCs from the set without use of a lookup table. The sufficient statistic is given and proven to allow for maximal ratio combining (MRC) by the intended receiver for all STBCs in the set. An algorithm is offered for the UE to update the MRC matrix in use as the STBC alternates. Definitions are provided for cryptograms, key residues (KRs), key residue classes (KRCs), and message and cryptogram residue classes pertaining to STBC PLS schemes. These definitions are used to present analysis of the information-theoretic security of the proposed PLS scheme to include message and key equivocation. Theoretical expected bit error rate (BER) for a passive eavesdropper is proven and plotted along with Monte Carlo simulations for confirmation. Discussion of different attack models is provided. Cost and attack complexity are compared between the proposed scheme and two related techniques from the literature.

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.

Greedy Code Search Based Memetic Algorithm for the Design of Orthogonal Polyphase Code Sets

Multiple-input-multiple-output (MIMO) radar has received significant attention because it offers broad design freedom and superior performance. Polyphase code sets with low autocorrelation sidelobe peaks and low cross-correlation peaks, also known as orthogonal polyphase code sets, can be used as transmission signals by MIMO radar. We present an effective algorithm named the greedy code search-based memetic algorithm (MA-GCS) to design such code sets. MA-GCS is a novel variation of the new evolutionary search, which can be used to design only a single binary sequence with low autocorrelation peaks. MA-GCS integrates an evolutionary search for global searches and a GCS for local searches to improve the accuracy of solutions. Moreover, an accelerating algorithm is designed to reduce the computational complexity of the GCS-based local search. The computational complexity of our algorithm is derived and compared with other algorithms. It is demonstrated by the experimental results that our algorithm is truly effective. On one hand, the code sets designed using our proposed algorithm have better autocorrelation and cross-correlation properties than other methods. On the other hand, the time consumed is acceptable. In addition, the influence of the code set parameters on the performance of the design results is also investigated.

Modified hybrid interference cancellation algorithm for uplink cognitive radio transmission based on overloaded DS-CDMA

In this paper, cognitive radio network architecture based on overloaded direct sequence code division multiple access (O-DS-CDMA) is proposed. In this method, secondary users are enabled to share the available bandwidth with the existing primary users. Two sets of orthogonal Gold codes are used to support the primary and secondary users simultaneously. Orthogonality between the spreading codes is lost due to non-zero cross correlation between the codes and timing synchronisation error in the uplink transmission, which causes interference among primary and secondary users. In this paper, a modified hybrid parallel/successive interference cancellation algorithm is proposed for the primary and secondary user base station receivers with multiple antennas, to suppress the interference among the users. Interferences among same group users are cancelled using parallel interference cancellation and the interferences between groups are cancelled using successive interference cancellation. The simulation results show that, the proposed modified interference cancellation algorithm improves the BER performance of the system significantly.

Design and modeling of electrode networks for code-division multiplexed resistive pulse sensing in microfluidic devices.

A typical microfluidic device sorts, captures or fractionates sample constituents by exposing them to discriminating microenvironments. Direct electronic acquisition of such manipulation by a network of integrated sensors can provide a fast, integrated readout, replacing otherwise required microscopy. We have recently introduced a sensor technology, Microfluidic CODES, which allows us to multiplex resistive pulse sensors on a microfluidic device. Microfluidic CODES employs a network of micromachined coplanar electrodes such that particles passing over these electrodes produce distinguishable code sequences. In this paper, we explain the design process to specifically generate an orthogonal digital code set for an efficient and accurate demultiplexing of the sensor signals. We also introduce an equivalent circuit model for a network of code-multiplexed resistive pulse sensors by utilizing the Foster-Schwan model and conformal mapping, to model dynamic cell-electrode interaction in a non-uniform electric field. Our results closely match with both experimental measurements using cell lines and finite element analysis. The coding and modeling framework presented here will enable the design of code-division multiplexed resistive pulse sensors optimized to produce desired waveform patterns to ensure reliable and efficient decoding.

Transmission scheduling in optical CDMA networks using hybridized overlap and threshold (HOT) scheduling algorithm

The bane of optical network is multiuser interference as a result of codewords overlap from different nodes simultaneously transmitting. Transmission scheduling is a good interference avoidance scheme which helps prevent throughput degradation at high offered load in an optical code division multiple access local area network. Interference avoidance consists of state estimation and transmission scheduling. This work examines different scheduling algorithms and parameter variations. This work investigated the performance of three scheduling algorithms (Pure Selfish Scheduling, Threshold Scheduling and Overlap Section Scheduling) against the ALOHA CDMA and our novel Hybrid--Hybridized Overlap and Threshold Scheduling--HOT algorithms using the modified padded prime codeset. The performance of the scheduling algorithms are measured in terms of its normalized network throughput, packet error rate and the average number of codewords allow into the line against the normalized offered load. The analysis shows that under this condition, the Hybridized Overlap--Threshold scheduling perform best and has throughputs as high as the 52 % with nearly zero packet error rate while the non-scheduled algorithm produce a throughput as low as 10 % and very high error rate at maximum offered load. Overall, the Threshold Scheduling and HOT algorithm are head to head and performed best in terms of normalized network throughput, however the HOT scheduling is best in terms of the packet error rate. Analysis also shows that the throughput is not affected by changes in codeset length and the mean packet size but it is affected by changes in the codeset weight. The study also analyzes the performance of the network under a bimodal packet distribution and with the Prime code codeset family. Optical Orthogonal Codeset and the Prime codeset family are used in the study under the assumption of perfect state estimation; that all nodes have the same view of the network and the transmission lines and the distance between the nodes and the central star coupler is assumed to be zero. A novel hybrid Scheduling Algorithm, the HOT Scheduling which proved better than traditional Scheduling Algorithms is peddled here.

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.

Performance Analysis of Uplink Cognitive Radio Transmission based on Overloaded MC-DS-CDMA

This paper reports a cognitive radio network architecture based on overloaded multicarrier direct sequence code division multiple access (O-MC-DS-CDMA). The O-MC-DSCDMA technique combines CDMA with a multicarrier modulation technique to overcome the channel fading effects. In this technique, secondary users are enabled to share the available bandwidth with the existing primary users. Two sets of orthogonal Gold codes are used to support the primary and secondary users simultaneously. The orthogonality between the spreading codes is lost due to the non-zero cross correlation between the codes and the timing synchronization error in the uplink transmission, which causes interference between primary and secondary users. This paper proposes two modified hybrid parallel/successive interference cancellation techniques for primary and secondary user base station receivers with multiple antennas to suppress the interference among users. Interference among the same group of users is cancelled by parallel interference cancellation and the interference among groups is cancelled using successive interference cancellation. The simulation results confirmed that the proposed modified interference cancellation techniques show better BER performance over conventional interference cancellation techniques.

Anti-Collision Technique of SAW Tags Using Walsh Code

—In view of the inefficiency of coding, the complexity of signal extraction and the strict demands of machining in the existing multiple SAW tags system, an anti-collision technique based on Walsh Code was proposed. First, it encodes the 2PSK using the single antenna transmission structure, then it implements the orthogonal encoding of each tag in a multiple SAW tags system using Walsh coding, and finally the encoding information of each tag is acquired by reading the echo signals from the reader and doing cross-correlation operation with each code block in the orthogonal code-set. The proposed approach incorporates both the coding efficiency and the processing technology, simplifies the complexity of signal extraction, and achieves the goal of anti-collision of multiple SAW tags system. The theoretical analysis and simulation verify the feasibility of this technique.

A New Method for Generating a Zero Mean Self-Balanced Orthogonal Chaotic Spread Spectrum Codes

Spread spectrum technique becomes one of the most important communication techniques in the recent decades. It provides high security, in addition to its resistance to the various interference and fading types. One of the most important parameter in the spreading process is the spreading code used in the spreading process, especially in the direct sequence spread spectrum. Recently, many researches focused on the chaotic codes, due to its attractive security properties, in addition to its availability to generate a huge number of spreading codes. This property is very useful in the multi-access applications. However, as the number of the MAI is increased, the performance of the chaotic codes is degraded. This paper presents a new method to generate a set of orthogonal self-balanced chaotic codes. The results show that the presented method generates a set of chaotic codes with correlation properties much better than the traditional chaotic code. The results show also that the BER performance of the presented orthogonal chaotic codes is superior and outperforming the BER performance of the traditional chaotic codes in addition to the PN sequences.

An efficient multiple access interference suppression scheme in asynchronous femtocells

This work considers a code division multiple access (CDMA)-based femtocell system where a fixed set of subscribed users communicate simultaneously to a femtocell access point (FAP) in an asynchronous fashion during the uplink. The main goal of this paper is to present an augmentation protocol for the physical layer of the CDMA2000 femtocell standard with focus on the multiple access interference (MAI) suppression. The above-closed access femtocell uses a unique set of cyclic orthogonal binary codes to eliminate the MAI caused by packet collisions. This property ensures that the time and data rate asynchronicity of active nodes in a femtocell produces a zero MAI situation at the FAP. The work investigates the optimality and the effectiveness of such codes in femtocells from the link bit error rate performance in a practical Rayleigh-fading environment, where Kalman filtering is used at the FAP for the channel estimation. Theoretical findings are verified by simulation evaluations and it is shown numerically a significant improvement in the performance of the proposed scheme when compared with conventional non-cyclic orthogonal codes in a Rayleigh-fading channel in the asynchronous femtocell.

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.

Multiplexing schemes for homomorphic cryptosystems

We present in this article two secure multiplexing and demul- tiplexing schemes that use homomorphic properties from known public key cryptosystems. One scheme is suitable for cryptosystems with addi- tive homomorphic properties such as Paillier and Benaloh cryptosystems. The proposed scheme employs a modification of Hadamard codes to generate a set of orthogonal codes over Z3. The other one is suitable for cryptosystems with multiplicative homomorphic properties such as RSA and ElGamal. Both schemes might be used in voting and auction systems where anonymity of the individuals is crucial.

Polyphase orthogonal sequences design for opportunistic array radar via HGA

Opportunistic array radar (OAR) is a new generation radar system based on the stealth of the platform, which can improve the modern radar performance effectively. Designing the orthogonal code sets with low autocorrelation and cross-correlation is a key issue for OAR. This paper proposes a novel hybrid genetic algorithm (HGA) and designs the polyphase orthogonal code sets with low autocorrelation and cross-correlation properties, which can be used in the OAR system. The novel algorithm combines with simulated annealing (SA) and genetic algorithm (GA), adds in keeping best individuals and competition in small scope, and introduces grey correlation evaluation to evaluate fitness function. These avoid the premature convergence problem existed in GA and enhance the global searching capability. At last, the genetic results are optimized to obtain the best solution by using greedy algorithm. The simulation results show that the proposed algorithm is effective for the design of orthogonal phase signals used in OAR systems.

Target Detection Using Orthogonal Polyphase MIMO Radar Waveform against Compound Gaussian Clutter

This paper mainly deals with the target detection using orthogonal Polyphase Multiple Input Multiple Output (MIMO) radar waveforms against compound-Gaussian clutter with an unknown covariance matrix. The design of orthogonal code sets with correlation properties can effectively improve the radar performance by transmitting orthogonal waveforms optimized by Particle Swarm Optimization Algorithm (PSO). The space-time coding MIMO radar model has adopted, and developed to compound-Gaussian case. The GLRT is developed by assuming known covariance matrix, and then, a suitable estimate based on secondary data is inserted into the detector to make fully adaptive. The simulation results show that the orthogonal waveform and the GLRT used in MIMO radar Model can provide a good performance in spikier clutter.

Method of Generating Multiple Sets of Orthogonal Codes with Wide Choice of Spreading Factors

This paper presents a generic method to construct multiple sets of orthogonal codes for application in direct sequence spread spectrum systems. The plurality of orthogonal sets is generated using any single two-level autocorrelation sequence of period one less than the desired spreading factor of the orthogonal codes. The proposed method hence generates orthogonal codes of all spreading factors for which a corresponding two-level autocorrelation sequence exists. The resulting orthogonal sets with wide choice of spreading factors is desirable in synchronous direct sequence spread spectrum systems. The sets can be generated such that they do not contain the codeword with single polarity as in the case of Walsh-Hadamard codes and orthogonal sets generated from cyclic shifts of two-level autocorrelation sequences. This renders all codes in the generated sets with an effective spreading gain. The generation method also encompasses a procedure to generate N-1 sets with low inter-set correlation for application to oversaturated spread spectrum systems.