Technologies for Cost-Effective udWDM-PONs

A comparison of AMI and NRZ coding schemes in a 636 Mbit/s SF-FSK system is performed. The system performances for a 223−1 sequence show that NRZ-coding of a three-electrode DFB transmitter laser and AMI-coding of a conventional DFB transmitter laser are comparable to within 0.5 dB. Both perform 3.5 dB better than NRZ-coding of the conventional DFB laser at a 10−9 bit error rate.

Distributed feedback lasers with reflecting ends can support a mode in the energy gap that is exponentially confined to the end reflectors. This mode can become the lasing mode in a laser having one high reflecting and one low reflecting end. We have quantitatively compared the properties of such a laser to more conventional DFB lasers having two uncoated cleaved facets or one uncoated and one low reflecting facet. This comparison required computing a distribution of properties for each laser design because the phases of the two end reflections have random values. The gap mode is inherently compact, and the laser favoring this mode has extremely high single-mode selectivity, excellent quantum efficiency, and good resistance to external reflections, when only one Bragg length long. The conventional laser designs have less mode selectivity and require cavity lengths of about two Bragg lengths to reach their optimum performance.

Due to the ever‐growing applications and services of the Internet of Things (IoT), designing energy‐efficient and spectral‐efficient transmission schemes to support IoT devices for the 6G space–air–ground integrated networks becomes much more challenging. Fortunately, energy harvesting (EH) and cognitive radio (CR) technologies have been proposed to alleviate these challenges. Inspired by this fact, this paper studies the issue of spectrum reuse in terms of spectrum utilization efficiency (SUE) in the energy harvesting cognitive radio network (EH‐CRN), where multiple primary transceiver pairs, one multi‐antenna secondary transmitter (ST), and one secondary base station (SBS) coexist. To characterize the impact of small‐scale fading and improve the SUE of the EH‐CRN with perfect spectrum sensing (SS), an adaptive scheme concerning SS, channel selection, EH, and data transmission (SCED) scheme are proposed, where the ST selects the channels for SS based on the residual energy, and adjusts the duration of EH and data transmission with respect to the sensing results. Then the Markov decision process problem of SUE is formulated, which is challenging due to the infinite system space and action space. To tackle the Markov decision process problem, the system space and action space are discreted, and divide the ST into the energy‐limited case and energy‐sufficient case according to specific energy condition. Moreover, theoretical results are extended to the EH‐CRN with imperfect SS. Numerical results show that the SUE under the SCED scheme in perfect SS and imperfect SS scenarios is better than that under other schemes.

We show 8 × 11.5-Gb/s (10-Gb/s after coding) optical OFDM transmission over 1000 km SSMF with conventional DFB lasers and direct-detection. Compared with the coherent-detection using ECL lasers, DFB lasers and direct-detection can significantly reduce the system complexity and cost.

Recently, the use of LTE in unlicensed spectrum (LTE-U) has gained a lot of attention. One of the daunting tasks before any such employment was to ensure the fair sharing of unlicensed spectrum between LTE-U and Wi-Fi radio access technologies (RATs), which now seems to be well addressed in the literature. However, along with fair sharing, the efficient utilization of unlicensed spectrum is also of profound significance, which pushes the need for coordination between LTE-U and Wi-Fi. Hence, this letter proposes a novel LTE-U and Wi-Fi (LAW) inter-RAT coordination mechanism for a more efficient utilization of the unlicensed spectrum. The aim is to address the inter-RAT hidden terminal problem between LTE-U and Wi-Fi and, thereby, offer better spectral efficiency. We modify the regular clear-to-send (CTS)-to-self frame and suggest the transmissions of modified CTS-to-self from LTE-U nodes to solve this hidden terminal issue. Further gains are extracted by allowing the simultaneous transmissions of LTE-U and Wi-Fi whenever possible.

The most noted effect of rapid growth in wireless networks in recent years has been the issues of spectrum usage and management because of its importance in wireless communication as the medium of data transmission. Efficient utilization of spectrum has been the major concerns in spectrum management over recent years because of the notion that radio spectrum is scarce, finite, and non-replicable. New technologies find it difficult to be allocated frequencies for their operations because most usable frequencies have already been allocated to licenced users while the unlicenced spectrum bands are becoming overcrowded. Researches have however shown that some of the allocated spectrum bands are not been used at some particular time in a particular location. The development of technologies like 4 th generation (4G) technology, Ultra Wide Band (UWB) techniques, Software-defined Radios (SDRs), and Cognitive Radios (CRs) help to improve the overall utilization of the limited spectrum. This paper surveyed these technologies and their impact in improving spectrum efficiency in terms of spectrum management and utilization. The paper concluded that dynamic spectrum access (DSA) technologies have greater impact when compare with other technologies. Cognitive Radios in particular have the potentials to substantially improve spectrum efficiency by opportunistically using spectrum. Spectrum efficiency in this context means that a large number of users are able to use available spectrum.

Dynamic spectrum access (DSA), enabled by cognitive radio technologies, has become a promising approach to improve efficiency in spectrum utilization, and the spectrum auction is one important DSA approach, in which secondary users lease some unused bands from primary users. However, spectrum auctions are different from existing auctions studied by economists, because spectrum resources are interference-limited rather than quantity-limited, and it is possible to award one band to multiple secondary users with negligible mutual interference. To accommodate this special feature in wireless communications, in this paper, we present a novel multi-winner spectrum auction game not existing in auction literature. As secondary users may be selfish in nature and tend to be dishonest in pursuit of higher profits, we develop effective mechanisms to suppress their dishonest/collusive behaviors when secondary users distort their valuations about spectrum resources and interference relationships. Moreover, in order to make the proposed game scalable when the size of problem grows, the semi-definite programming (SDP) relaxation is applied to reduce the complexity significantly. Finally, simulation results are presented to evaluate the proposed auction mechanisms, and demonstrate the complexity reduction as well.

Dispersion power penalties arising from chromatic dispersion and mode partition noise are discussed. Using chromatic dispersion measurements made on fifty 30 km spans in a MCI fiber-optic system, maximum repeater spacings for a hypothetical 565 Mb/s system (using conventional fibers and lasers at 1300 nm) and a 1.6 Gb/s system (using conventional fibers and DFB lasers at 1550 nm) are calculated. For the DFB laser, power penalties due to chirping, existence of a side mode, and mode partition noise are calculated.

The advent of 5G era and the increase of terminal’s numbers have led to increasing demand for spectrum resources and energy simultaneously. Therefore, this paper studies how to combine the cognitive radio (CR) and the Simultaneous Wireless Information and Power Transfer (SWIPT) technology effectively in a multiuser scenario, in which the spectrum utilization and energy efficiency are both improved. Firstly, the system model is designed of above cognitive SWIPT system, in which the cognitive users (CU) can choose spectrum access policy based on the amount of data transmission of licensed user. And then, according to cognitive users’ channel conditions and forwarding power, a concept of trust value and different relay selection policies is proposed. Subsequently, the according system ergodic capacity is analyzed. Finally, simulation results of system performance are provided to validate the analytical results. It shows that cognitive SWIPT technology can improve the system ergodic capacity and the spectrum access opportunities of cognitive users effectively, thereby improving the efficiency of energy and spectrum utilization.

Cognitive radio technology offers promising potential to address the growing scarcity of radio spectrum by intelligently and dynamically accessing underutilized frequency bands. This adaptability allows for efficient spectrum utilization, reduced interference, and improved network performance, making it a vital component for future wireless communication systems and emerging applications. The cognitive radio network (CRN) continues to face challenges in the areas of spectrum management and security. With the continuous development and advancement of wireless communication systems, the security challenges associated with CRN are increasing. In recent years, there has been a significant demand for advanced security features in CRNs. This led to an increase in the publication of literature on this important and widely recognized issue, both for the purpose of enhancing understanding and for functional considerations. However, it remains unclear how far and in what direction CRN security research has progressed. This study attempts to comprehensively examine the current state of research pertaining to the security of CRNs with the aim of addressing this concern. Out of 1506 publications obtained from the Scopus database, 458 articles are screened, and a bibliometric analysis is performed on those articles. Using the Biblioshiny and VOSviewer tools, thorough descriptive and network analysis of bibliometric data produced some astonishing findings. The results support the idea that CRN security is essential for achieving the goal of efficient and secure spectrum utilization. This study deepens our comprehension of academic literature and conceptual development, shedding light on how to build a solid conceptual footing and chart the course for future research.

For an SCPC/FDMA digital mobile radio system, a channel structure supporting ISDN services is described. Three kinds of radio channels are proposed offering ISDN services with efficient spectrum utilization. They are: an information channel, control channel, and packet channel. The effects of diversity and FEC (forward error correction) are discussed for the improvement of digital transmission quality and frequency spectrum utilization. Some studies are presented regarding quality objectives for bearer services under multipath fading environments. >

The rapid escalation of Internet traffic and increasingly heterogeneous service demands impose stringent requirements on optical networks for dynamic resource scheduling, efficient spectrum utilization, and automated operation. Elastic optical networks (EONs) are regarded as a promising solution, yet their performance remains constrained by two critical challenges: routing, modulation format, and spectrum allocation (RMSA) and spectrum defragmentation (SD). Existing approaches predominantly focus on optimizing one of these tasks, which may lead to limited adaptability and suboptimal network efficiency. To address this gap, we propose an asynchronous cooperative multi-agent deep reinforcement learning framework, termed MADRL-JRASD, for the joint optimization of RMSA and proactive SD. The framework incorporates an RMSA agent with dynamic allocation capability and an SD agent with autonomous decision-making ability, coordinated through an asynchronous architecture that enables adaptive responses to environmental changes. Invalid-action masking and carefully designed reward functions are further integrated to enhance training stability and convergence. Comprehensive evaluations over three representative topologies demonstrate that MADRL-JRASD reduces the blocking probability by up to 81% compared with RMSA heuristics without SD and achieves an 85% reduction in overhead relative to heuristic algorithms combining RMSA and SD that attain similar blocking performance. Moreover, the sensitivity analysis shows that the SD agent improves spectrum utilization and that multi-agent cooperation enhances global decision coordination, while action masking and reward design jointly strengthen the convergence and efficiency of MADRL-JRASD.

In spectrum sharing, a spatial separation region is defined around primary users (PUs) to protect them from secondary user (SU)-induced interference. This protection region — referred to by a number of names, such as an exclusion zone (EZ) or a protection zone (PZ) — has a static boundary, and this boundary is determined very conservatively to provide an additional margin of protection for the PUs. This legacy notion of interference protection is overly rigid, and often results in poor spectrum utilization efficiency. In this paper, we propose a novel framework for prescribing interference protection for the PUs that addresses some of the limitations of legacy EZs. Specifically, we introduce the concept of Multi-tiered Incumbent Protection Zones (MIPZ), and show that it can be used to dynamically adjust the PU's protection boundary based on the radio environment, network conditions, and the PU interference protection requirement. MIPZ can serve as an analytical framework for quantitatively analyzing a given PZ to gain insights on and determine the tradeoffs between interference protection and spectrum utilization efficiency. It allows a number of SUs, say N, to operate closer to the PU, and improves the overall spectrum utilization efficiency while ensuring a probabilistic guarantee of interference protection to the PU. We leverage the combined power of database-driven spectrum sharing and stochastic optimization theory for dynamically computing the zone boundary and the value of N. Using extensive simulation results, we demonstrate that the proposed framework improves spectrum utilization efficiency by adapting to the changing interference environment through dynamic adjustments of the zone boundary.

A conventional semiconductor DFB laser is self-injection-locked to a CMOS-foundry- fabricated ultra-high Q silicon nitride microresonator, suppressing high-offset frequency noise to 0.2 Hz2 Hz-1 and yielding instantaneous linewidth of 1.2 Hz.

We demonstrate that high-coherence Si/III-V hybrid lasers are much more robust than conventional III-V DFB lasers against both coherent and incoherent optical feedback by examining the frequency noise power spectral density of the lasers.