Enhance Spectrum Efficiency Research Articles

Dynamic system level frequency spectrum allocation scheme based on cognitive radio technology

Cognitive radio is being widely discussed, and resource allocation scheme is drawing a lot of attention. Although the existed resource allocation strategies have successfully enhanced spectrum efficiency, some critical challenges still remain unanswered such as the jointly consideration of the efficiency and fairness, the rational description of the spectrum resources, and the execution mode of the spectrum allocation. This paper presents a system level dynamic frequency spectrum allocation scheme based on a central heterogeneous network architecture, evaluates the matching degree of the spectrum demand and the available spectrum resources with corresponding matrices, jointly considers the efficiency and fairness of different cognitive radio systems. Simulation results and the application scenario are also presented and analyzed.

Joint overlay and underlay resource allocation with weighted fairness in OFDM‐based cognitive radio systems

SummaryIn this paper, the problem of hybrid overlay and underlay spectrum access is investigated for OFDM‐based cognitive radio (CR) systems. Both the metrics for system (e.g. capacity) and users (e.g. fairness) are integrated into the unified framework of weighted‐capacity maximization with the interference constraint in CR systems. For easing the procedure of resource allocation, two criteria, respectively, for subcarrier assignment and power allocation are theoretically derived based on the Karush–Kuhn–Tucker conditions. Under the guidance of the two criteria, max‐capacity subcarrier assignment and optimal power allocation are proposed to flexibly distribute spectrum resources to secondary users. In order to reduce the computational complexity further, a suboptimal power allocation algorithm, referred to as cap‐limited waterfilling, is also presented by decomposing the interference constraint. Simulation results show that the capacity and fairness performance of the proposed algorithms is considerably better than the conventional ones in references. The proposed suboptimal algorithm with substantially lower complexity approaches to optimal power allocation in the vicinity of only 1% performance gap. Meanwhile, joint access model is greatly beneficial to spectrum efficiency enhancement in CR systems. Copyright © 2014 John Wiley & Sons, Ltd.

Spectrum and Energy Efficient Relay Station Placement in Cognitive Radio Networks

Cognitive radio technology enables secondary users (SUs) to opportunistically use the vacant licensed spectrum and significantly improves the utilization of spectrum resource. Traditional architectures for cognitive radio networks (CRNs), such as cognitive cellular networks and cognitive ad hoc networks, impose energy-consuming cognitive radios to SUs' devices for communication and cannot efficiently utilize the spectrum harvested from the primary users (PUs). To enhance the spectrum and energy efficiencies of CRNs, we have designed a new architecture, which is called the Cognitive Capacity Harvesting network (CCH). In CCH, a collection of relay stations (RSs) with cognitive capability are deployed to facilitate the accessing of SUs. In this way, the architecture not only removes the requirement of cognitive radios from SUs and reduces their energy consumption, but also increases frequency reuse and enhances spectrum efficiency. In view of the importance of the RSs on the improvement of spectrum and energy efficiencies, in this paper, we study the RS placement strategy in CCH. A cost minimization problem is mathematically formulated under the spectrum and energy efficiency constraints. Considering the NP-hardness of the problem, we design a framework of heuristic algorithms to compute the near-optimal solutions. Extensive simulations show that the proposed algorithms outperform the random placement strategy and the number of required RSs obtained by our algorithms is always within 2 times of that in the optimal solution.

Spectrum efficiency of nested sparse sampling and coprime sampling

This article addresses the spectrum efficiency study of nested sparse sampling and coprime sampling in the estimation of power spectral density for QPSK signal. The authors proposed nested sampling and coprime sampling only showed that these new sub-Nyquist sampling algorithm could achieve enhanced degrees of freedom, but did not consider its spectrum efficiency performance. Spectral efficiency describes the ability of a communication system to accommodate data within a limited bandwidth. In this article, we give the procedures of using nested and coprime sampling structure to estimate the QPSK signal’s autocorrelation and power spectral density (PSD) using a set of sparse samples. We also provide detailed theoretical analysis of the PSD of these two sampling algorithms with the increase of sampling intervals. Our results prove that the mainlobe of PSD becomes narrower as the sampling intervals increase for both nested and coprime sampling. Our simulation results also show that by making the sampling intervals, i.e., N1 and N2 for nested sampling, and P and Q for coprime sampling, large enough, the main lobe of PSD obtained from these two sub-Nyquist samplings are much narrower than the original QPSK signal. That is, the bandwidth B occupancy of the sampled signal is smaller, which improves the spectrum efficiency. Besides the smaller average rate, the enhanced spectrum efficiency is a new advantage of both nested sparse sampling and coprime sampling.

Study on Environmental Improvement for DTV White Space Utilization with Narrow Band System

Some idle spaces in the TV band, the so-called Digital Dividend have emerged through the TV channel rearrangement process as the one of the activities for DTV transition. Various wideband services including spectrum sensing application are currently being reviewed as DTV White Space application in order to cope with the wireless internet environment. However, it is hard to expect lots of DTV White Space due to geographical conditions and interference issues with broadcasters as incumbent users in the DTV band. In this paper, the authors are suggesting measures for DTV White Space usability by reviewing the availability of White Space from diverse aspects in order to improve the usage environment of DTV White Space. As a part of this study, narrowband applications have been considered for practical use of White Space from the aspect of efficient use of the DTV spectrum. Related to this, the TETRA system has been applied to this study as a narrowband application for DTV White Space. In addition, this study has suggested a direction for a DTV White Space management scheme that will be able to enhance spectrum efficiency by considering unoccupied channel conditions according to the density of DTV transmitters and relays at three DTV pilot regions in Korea, i.e. Uljin, Gangjin and Danyang. Especially, there has been a consideration of the regulatory criteria compatibility between the US and Korea in order to review the possibility of the physical expansion of DTV White Space, this study has been based on two kinds of minimum field strengths at part 73 of 47 CFR. Through computed calculations, the interoperable range of the TETRA system was reviewed according to the operating modes and power classes.

Spectrally Efficient Diversity Exploitation Schemes for Downlink Cooperative Cellular Networks

In this correspondence, we advocate the exploitation of direct links for downlink cooperative cellular networks, where one base station (source) communicates with one out of N mobile users (destinations) by using a half-duplex decode-and-forward (DF) relay. Motivated by the potential spectrum-efficiency enhancement, we propose two spectrally efficient schemes for the diversity exploitation of the considered systems in a homogeneous network topology. By scheduling the user with the best direct link to access the channel, an incremental DF relaying scheme is first presented, and its outage behavior is analyzed, revealing that this scheme can achieve full diversity order (N + 1). To further enhance transmission robustness against fading (in terms of outage probability), an improved scheme is also proposed, which substantially utilizes the opportunistic scheduling mechanism when the direct transmission fails. Outage analysis for this scheme shows that, aside from achieving full diversity order, it can further improve the transmission reliability to fading, compared with the preceding one. In addition, it is indicated that the expected spectral efficiency of the proposed schemes approaches that of direct transmission in the high-signal-to-noise-ratio (SNR) regime. Finally, adjustment of the proposed schemes for heterogeneous network topology is presented, and the corresponding outage behavior is characterized as well.

Cognitive Radio Network Tomography

The cognitive radio network (CRN), as a promising technique in future wireless communication networks, shall execute some critical functionalities to enhance existing wireless networks, such as network reconfigurability to adaptively select networks (e.g., in IEEE P1900.4 and ETSI-RSS), spectrum opportunity utilization for transmissions over opportunistic links to enhance spectrum efficiency (e.g., in IEEE 802.22), and further cooperative relays among cognitive radios (CRs) and nodes of coexisting multiradio systems, including heterogeneous primary systems. To support multilink operations and networking functions in CRN, traditional spectrum sensing is not enough, and we thus develop CRN tomography to meet the general needs of CRN operations at both the link and network levels. Borrowing the concept from medical/Internet tomography via statistical inferring, we establish the framework and methodology of CRN tomography that can be passive monitoring or active probing defined over link- or network-level parameter inference. Generally speaking, conventional CR spectrum-sensing techniques belong to the category of the passive link-level monitoring. Multiple-system sensing and identification can be considered as a sort of passive network-level CRN tomography. We further propose active link-level CRN tomography by examining the radio resource for transmissions. Finally, CRN tomography using active network-level probing is illustrated by the estimation of successful packet-transmission probability in network operations. This paper initiates explorations of CRN tomography obtaining the required parameters at the link and network levels for successful CRN operations.

Novel overlay/underlay cognitive radio waveforms using SD-SMSE framework to enhance spectrum efficiency- part i: theoretical framework and analysis in AWGN channel

Recent studies suggest that spectrum congestion is primarily due to inefficient spectrum usage rather than spectrum availability. Dynamic spectrum access (DSA) and cognitive radio (CR) are two techniques being considered to improve spectrum efficiency and utilization. The advent of CR has created a paradigm shift in wireless communications and instigated a change in FCC policy towards spectrum regulations. Within the hierarchical DSA model, spectrum overlay and underlay techniques are employed to enable primary and secondary users to coexist while improving overall spectrum efficiency. As employed here, spectrum overlay exploits unused (white) spectral regions while spectrum underlay exploits underused (gray) spectral regions. In general, underlay approaches use more spectrum than overlay approaches and operate below the noise floor of primary users. Spectrally modulated, spectrally encoded (SMSE) signals, to include orthogonal frequency domain multiplexing (OFDM) and multi-carrier code division multiple access (MC-CDMA), are candidate CR waveforms. The SMSE structure supports and is well suited for CR-based software defined radio (SDR) applications. This paper provides a general soft decision SMSE (SDSMSE) framework that extends the original SMSE framework to achieve synergistic CR benefits of overlay and underlay techniques. This extended framework provides considerable flexibility to design overlay, underlay and hybrid overlay/underlay waveforms that are scenario dependent. Overlay/underlay framework flexibility is demonstrated herein for a family of SMSE signals, including OFDM and MC-CDMA. Analytic derivation of CR error probability for overlay and underlay applications is presented. Simulated performance analysis of overlay, underlay and hybrid overlay/underlay waveforms is also presented and benefits discussed, to include improved spectrum efficiency and channel capacity maximization. Performance analysis of overlay/underlay CR waveform in fading channels will be discussed in Part II of the paper.

Cognitive radio architecture evolution: annals of telecommunications

Cognitive radio research has developed dynamic radio spectrum management to enhance spectrum efficiency, e.g., as secondary users in unused TV bands. The location and user context of the mobile wireless user that regulatory bodies and lawmakers view as significant to spectrum interference policies have not been addressed as thoroughly. In addition, quality of service (QoS) provides a starting point but does not guarantee quality of experience (QoE) that depends on quality of information (QoI) which is a function of place, time, and user state in a social setting (e.g., commuting, shopping, or in need of medical assistance). This paper considers the evolution of cognitive radio architecture (CRA) from dynamic spectrum access (DSA) to QoE via an interdisciplinary perspective. Machine perception in visual, acoustic, speech, and text domains can cue the automatic detection of user state in stereotypical situations, enabling cognitive nodes and networks to select from among radio bands and modes more appropriately, thus enabling cognitive wireless networks (CWNs) to deliver higher QoE within technical policy constraints, in a way that makes cost-effective use of embedded and distributed computational intelligence. The control of networks of such cognitive radios requires advances in policy language architectures, so this paper introduces cognitive linguistics for policy languages.

Spectrum Efficiency Enhancement in Dynamic Space Coded Multiple Access (DSCMA) System

In cellular mobile communication systems using coded modulations, the spectrum efficiency of the system is related to the number of available codes. Recently, large area synchronous (LAS) CDMA codes, which exhibit a region called interference free window (IFW) within some delay-spread, have been accepted as one of fourth-generation (4G) wireless communication systems. However, the number of synthesized LAS codes is very low due to the low duty ratio of the sequence. In this paper, a dynamic space coded multiple access (DSCMA) scheme which utilizes the spatial diversity from smart antenna system is proposed to overcome the low spectrum efficiency in LAS CDMA system. In the DSCMA a modified version of LAS codes called LAS even ternary (LAS-ET) codes is proposed. These codes are used together with a novel algorithm called dynamic space code (DSC), which will decrease the code length so that the spectrum efficiency can be increased. By taking advantage of dynamic code reuse assignment in spatial diversity, the spectrum efficiency of the DSCMA can be further increased significantly.

Spectrum pooling: an innovative strategy for the enhancement of spectrum efficiency

This article describes the technical challenges that have to be met when implementing the interesting new technology of spectrum pooling. This notion represents the coexistence of two mobile radio systems within the same frequency range. It enables the secondary utilization of already licensed frequency bands as aimed at by several regulatory authorities worldwide. The goal of spectrum pooling is to enhance spectral efficiency by overlaying a new mobile radio system on an existing one without requiring any changes to the actual licensed system. Several demanding tasks originate from this idea. Some of them have been solved in recent research projects. Others are subject to ongoing investigations. Here, the state of the art in spectrum pooling is presented.

Spectrum resource allocation for wireless packet access with application to advanced cellular Internet service

The advanced cellular Internet service (ACIS) is targeted for applications such as Web browsing with a peak downlink transmission rate on the order of 1-2 Mbits/s using a wide-area cellular infrastructure. In order to provide bandwidth on demand using scarce radio spectrum, the medium-access control (MAC) protocol must: 1) handle dynamic and diverse traffic with high throughput, and 2) efficiently reuse limited spectrum with high peak rates and good quality. Most of the existing approaches do not sufficiently address the second aspect. This paper proposes a dynamic packet assignment (DPA) scheme which, without coordinating base stations, allocates spectrum on demand with no collisions and low interference to provide high downlink throughput. Interference sensing and priority ordering are employed to reduce interference probability. A staggered frame assignment schedule is also proposed to prevent adjacent base stations from allocating the same channel to multiple mobiles at the same time. Simulation results based on a packet data traffic model derived from wide-area network traffic statistics, which exhibit a self-similar property when aggregating multiple sources, confirm that this method is able to reuse spectrum efficiently in a large cellular system having many users with short active periods. Distributed iterative power control further enhances spectrum efficiency such that the same channel can be simultaneously reused in every base station.