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In this paper, two new families of asynchronous channel-hopping (CH) sequences—Symmetric Maximum-Length CH (SML-CH) Sequences and Relaxed Difference Set (RDS) of Maximum-Length CH (RDSML-CH) Sequences—are constructed. For the first time, the maximum-length sequences (also called as m-sequences) are used to create 2-D CH matrices with a reduced number of “jump” columns. The two new constructions carry the desirable properties of maximum rendezvous diversity (MRD) and even channel use (ECU) and, more importantly, have the shortest periods in their categories of constructions. Another contribution is on the embedment of optical orthogonal codes (OOCs) to eliminate “stay” columns in the RDSML-CH matrices, thus resulting in the first and only family of the asynchronous CH sequences that can asymptotically achieve the theoretical period lower bound. To support the RDSML-CH construction, a new shortened RDS algorithm for creating the OOCs with smaller weight-to-length ratios than the existing ones is proposed. Numerical and simulation analyses show that the two new constructions have a good balance of short period, MRD, ECU, short time-to-rendezvous (TTR) mean, small TTR variance, and short maximum-TTR, thus more suitable for practical CR wireless networks than the existing constructions. [ABSTRACT FROM AUTHOR]

In this article, the channel hopping (CH) method for the rendezvous process of secondary users in multi-channel CRAHNs is overviewed. With the evolution of the Internet of Things, design criteria of CH sequences targeting these applications are discussed. While channel collision among CH sequences is inherent in realistic CRAHNs, most prior works focused on sequence designs without addressing the channel collision problem. Hence, the concept of contention resolution in CRAHNs is introduced in this article, and a "multi-round" contention resolution mechanism is studied. To quantify the performance, the RS rate of the mechanism is presented and validated with computer simulation. Finally, the rendezvous time savings, which, in turn, can enhance data throughput, of the multi-round mechanism over a single-round one are investigated. [ABSTRACT FROM AUTHOR]

Besides designing channel-hopping (CH) sequences, finding good methods of communication rendezvous is important for improving spectral efficiency and alleviating traffic load of cognitive radio (CR) networks. In this paper, new asynchronous-symmetric CH sequences are constructed and their (channel overlap, even-channel-use, and pairwise shift invariance) properties are investigated. Their operations in three transmission scenarios involving different basic collision-avoidance mechanisms are analyzed and compared in terms of maximum time-to-rendezvous, rendezvous-success (RS) rate, and RS variance. This paper shows that the new sequences have shorter period, larger cardinality, and smaller RS variations than other CH sequences, thus supporting greater number of secondary users and more frequent and uniform rendezvous in the CR networks. [ABSTRACT FROM PUBLISHER]

Protocol sequences have recently been studied in collision channels without feedback for dynamic multiple-access mobile applications, such as wireless sensor and vehicular ad hoc networks. In this paper, a method of systematically adding mark chips into some families of prime sequences for the construction of protocol sequences with adjustable duty factors is investigated. Not relying on computer simulation only, new theoretical models of throughput and its variance are formulated to analyze the sequence performance by means of average hit probabilities. Numerical studies and computer simulations are performed to validate the new analytical models. With adjustable duty factors, these protocol sequences support flexible exchange between throughput and the number of active users. [ABSTRACT FROM PUBLISHER]

In this paper, a novel code-shifting technique, which can be added atop asynchronous incoherent optical code-division multiple-access systems without complex modifications, is proposed and studied. The new technique divides the time-slot (or chips), in which the optical pulses of codewords are located, into $g$ equal-width sub-chips; every pulse is randomly and independently shifted to start at one of the $g$ sub-chips of its own chip, where $g > 1$ is a positive integer. The effects of this random $g$-shift to the cross-correlation property and performance of asynchronous optical codes (of periodic cross-correlation functions of at most one) are formulated. Although it is found that the periodic cross-correlation functions are worsened to $3-2/g$, our theoretical and computer-simulation results show an unconventional finding that code performance improves as $g$ increases. [ABSTRACT FROM PUBLISHER]

Due to power restriction of some laser sources, the use of same power (per bit duration) in optical codes in incoherent optical code-division multiple-access multimedia networks with variable quality-of-services was previously studied. In those studies, the performance of double-weight codes with the maximum cross-correlation function λc=1 was exactly analyzed, but an approximation was only applied to the codes with λc > 1 due to mathematical complexity. In this paper, an exact analytical model of double-weight codes with an arbitrary λc ≥ 1 is formulated and validated with computer simulation. This general, more accurate performance model is also useful for power-sensitive applications, such as in-service monitoring and fiber-fault surveillance in optical networks and sensor-identification in fiber-sensor systems using optical codes for address or user identification. [ABSTRACT FROM PUBLISHER]

In this paper, the extended Reed-Solomon codes are modified to construct a new family of 2-D codes for asynchronous optical code-division multiple access (O-CDMA). In addition of having expanded and asymptotically optimal cardinality, these 2-D asynchronous optical codes can be partitioned into multiple tree structures of code subsets, in which code cardinality is a function of the (periodic) cross-correlation value assigned to the subset. The performance of these 2-D optical codes is analyzed and compared with that of the multilevel prime codes. Our results show that the unique partition property of the new optical codes supports a trade-off between code cardinality and performance for meeting different system requirements, such as user capacity and throughput. In addition, the multiple tree structures of the new codes potentially support applications that require rapid switching of many codewords, such as in O-CDMA-network gateway or in strategic environments where code obscurity is essential. [ABSTRACT FROM PUBLISHER]

In this paper, a new family of two-dimensional (2-D) wavelength-hopping time-spreading codes, which employs wave-length hopping algebraically under prime-sequence permutations on top of time-spreading optical orthogonal codes, is studied and analyzed. Different from other 2-D codes, our new codes allow the number of wavelengths and code length to be chosen independently and, at the same time, the code cardinality is a quadratic function of the number of wavelengths without sacrificing the maximum cross-correlation value (i.e., still at most one). They are particularly suitable for high bit-rate optical code-division multiple-access systems with broadband mode-locked lasers, in which the number of time slots is very limited, and system capacity can only be grown by increasing the number of wavelengths, rather than code length. Finally, a novel wavelength-aware detector for wavelength-hopping time-spreading codes is discussed and shown to provide improved code performance. [ABSTRACT FROM AUTHOR]

A two-dimensional wavelength-hopping time- spreading coding scheme has been recently studied for optical code-division multiple access, owing to maturity in fiber-Bragg grating (FBG) and arrayed-waveguide grating (AWG) technologies. Most of the optical codes designed for the scheme were based on an assumption, which may not be true in high data-rate systems, that the number of chips is higher than the number of available wavelengths. To provide a flexible code design without the assumption, this paper studies and analyzes a new family of carrier-hopping prime codes with expanded cardinality and ideal correlation properties. Flexible implementation of programmable AWG- and FBG-based coding hardware by using the wavelength-shift property of the codes is discussed. [ABSTRACT FROM AUTHOR]

Presents a study which proposed a multicarrier (multihopping) scheme for multilevel frequency-shift keying/frequency-hopping code-division multiple-access (FH-CDMA) systems. Information on the FH-CDMA systems; Performance analysis; Conclusions.

Studies the application of multilevel frequency-shift keying/frequency-hopping spread spectrum multiple access (MFSK-FH-SSMA) to wireless systems. Discussion on MFSK-FH-SSMA systems; Description of the system model; Performance of a system with one-hit FH patterns; Example of double-length FH patterns; Performance of the system with double-length patterns; Performance comparison of random and deterministic patterns.

Provides information on a study which explored the construction of multilength frequency-hopping (FH) codes by modifying the generalized prime codes (GPC). Construction of the GPC; Construction of multiple-length FH codes; Applications of the GPC.

Addresses the problem of constructing frequency-hopping codes for use in a fast frequency-hopping code-division multiple access cellular system with a K-cell frequency-reuse scheme. Frequency-hopping patterns; Cardinalities of the codes for use in the intracells; Maximum number of users which can be accommodated using the proposed scheme.

Due to power restriction of some laser sources, the use of same optical power in every bit duration (i.e., same bit power) of double-weight codes in optical code-division multiple access (O-CDMA) with differential quality-of-service (QoS) was previously studied and analyzed with approximated performance. In this paper, an exact analytical model is formulated and validated with computer simulation, establishing accurate relationships of code weight, chip power, and bit power with code performance. Besides better understandings the role of power control in variable-weight O-CDMA with differential QoS, such accurate analytical model is important for power-sensitive applications, such as in-service monitoring and fiber-fault surveillance in optical networks and sensor-identification in fiber-sensor systems with the use of optical codes. [ABSTRACT FROM AUTHOR]

In this paper, we propose a "two-level" frequency-hopping code-division multiple-access (FH-CDMA) scheme for wireless communication systems. The new scheme provides flexibility in the selection of modulation codes and FH patterns. By partitioning the modulation codes, our two-level scheme can be modified to support more possible users without increasing the number of FH patterns. The performance and spectral efficiency (SE) of the scheme are analyzed. Our results show that the partitioned two-level FH-CDMA scheme supports higher data rate and greater SE than Goodman's frequency-shift-keying FH-CDMA scheme under some conditions. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) wavelength-time coding schemes have recently been studied for optical code-division multiple access. In this paper, we propose a new family of 2D codes, which use "synchronized" quadratic congruence sequences for wavelength hopping and (n,w,2,2) optical orthogonal codes for time spreading. The new 2D codes provide larger (asymptotically optimal) code cardinality than other 2D codes by relaxing the maximum cross-correlation function from one to two. Our study shows that the heavier code weight supported by our 2D codes results in better code performance than some of previously proposed 2D codes (of the maximum cross-correlation functions of one and two). The new codes potentially support more subscribers and heavier bursty asynchronous traffic with gradual performance degradation as traffic load increases. [ABSTRACT FROM AUTHOR]

We propose a modified bipolar-bipolar code for wavelength-time optical code-division multiple access. The new code uses Gold sequences for time spreading, in place of Barker sequences in our previously proposed bipolar-bipolar code. The new code has a cardinality of N + 1 times greater than the original code, because there exist N + 2 Gold sequences, but only one Barker sequence, for a given code length N. Since the new code is modified from the original code, there is no increase in hardware complexity. The average performance of the new code is analyzed and found very close to that of the original code. In other words, the new code can support greater cardinality without worsening average performance or increasing hardware complexity. [ABSTRACT FROM AUTHOR]

To provide differential quality-of-service in optical code-division multiple access, variable-weight codes were proposed and analyzed under a conventional assumption of identical power in every optical pulses (i.e., same chip power). To account for power limit of some laser sources, we assume the use of same optical power in each bit duration (i.e., same bit power) in this paper. For illustration, we focus our study on double-weight codes under both same-chip-power and same-bit-power assumptions. A new and better approximate performance-analytical model for double-weight codes is developed and validated with computer simulation. We show that heavy-weight codes do not always perform better than light-weight codes under the same-bit-power assumption, contrary to previous findings under the same-chip-power assumption. [ABSTRACT FROM AUTHOR]