This paper considers the generalized cognitive radio channel where the secondary user is allowed to reuse the frequency during both the idle and active periods of the primary user, as long as the primary rate remains the same. In this setting, the optimal power allocation policy with single-input single-output (SISO) primary and secondary channels is explored. Interestingly, the offered gain resulting from the frequency reuse during the active periods of the spectrum is shown to disappear in both the low and high signal-to-noise ratio (SNR) regimes. We then argue that this drawback in the high SNR region can be avoided by equipping both the primary and secondary transmitters with multiple antennas. Finally, the scenario consisting of SISO primary and multi-input multi-output (MIMO) secondary channels is investigated. Here, a simple Zero-Forcing approach is shown to significantly outperform the celebrated Decoding-Forwarding-Dirty Paper Coding strategy (especially in the high SNR regime).
Measuring language complexity from hierarchical reuse of recurring patterns
Department of Systems Science, Faculty of Arts and Sciences, Beijing Normal University(北京师范大学文理学院系统科学系);International Academic Center of Complex Systems, Beijing Normal University(北京师范大学国际复杂系统学术中心);Department of Chinese Language and Literature, Faculty of Arts and Sciences, Beijing Normal University(北京师范大学文理学院中国语言文学系);Center for Linguistic Sciences, Beijing Normal University(北京师范大学语言学科学中心);School of Systems Science, Beijing Normal University(北京师范大学系统科学学院);Department of Mathematics and Applied Mathematical Sciences, University of Rhode Island(罗德岛大学数学与应用数学科学系);Department of Cell and Molecular Biology, University of Rhode Island(罗德岛大学细胞与分子生物学系)
Cognitive radios hold tremendous promise for increasing the spectral efficiency of wireless communication systems. In this paper, an adaptive bit allocation algorithm is presented for orthogonal frequency division multiplexing (OFDM) CR systems operating in a frequency selective fading environment. The algorithm maximizes the CR system throughput in the presence of narrowband interference, while guaranteeing a BER below a predefined threshold. The effect of imperfect channel estimation on the algorithm's performance is also studied.
We study power control and frequency band selection policies for multi-band underlay MIMO cognitive radio with the objective of maximizing the rate of a secondary user (SU) link while limiting the interference leakage towards primary users (PUs) below a threshold. The goal of the SU in each policy is to select one frequency band in each time slot and determine the transmit power. To limit the interference towards PU in time-varying channels, we propose fixed and dynamic transmit power control schemes which depend on PU traffic and the temporal correlation of channels between the SU and the PU.…
In this paper, we study partially overlapping co-existence scenarios in cognitive radio environment. We consider an Orthogonal Frequency Division Multiplexing (OFDM) cognitive system coexisting with a narrow-band (NB) and an OFDM primary system, respectively. We focus on finding the minimum frequency separation between the coexisting systems to meet a certain target BER. Windowing and nulling are used as simple techniques to reduce the OFDM out-of-band radiations, and, hence decrease the separation. The effect of these techniques on the OFDM spectral efficiency and PAPR is also studied.
Broadcast of localized TV content enables tailored content delivery catering to the requirements of regional user base. 5G multicast-broadcast service (MBS) requires a spectrally efficient broadcast solution that enables the change of content from one local service area (LSA) to another. A frequency reuse factor of unity between two adjacent LSAs causes their boundary region to become saturated with co-channel interference (CCI). Increasing the reuse factor will reduce the CCI at the cost of degrading the spectral efficiency. This paper addresses the frequency and transmit power planning which…
Reuse-1 systems operating in the sub-1 GHz UHF band are limited by substantial co-channel interference (CCI). In such orthogonal frequency division multiple access (OFDMA) cellular systems, the inter-sector or inter-tower interference (ITI) makes accurate signal recovery quite challenging as sub-1 GHz bands only support single-input single-output (SISO) links. Interference-aware receiver algorithms are essential to mitigate the ITI in such low-frequency bands. Such algorithms enable ubiquitous mobile broadband access over the entire homeland, say with >95% geographical coverage with quality of…
Performance Analysis of Spectrum Handoff for Cognitive Radio Ad Hoc Networks without Common Control Channel under Homogeneous Primary Traffic
认知无线电(CR)技术被认为是解决频谱稀缺问题的一种有效方法.由于CR网络的频谱变化性质,当授权用户重用频谱时,需要未授权用户执行频谱切换。在本文中,我们研究了频谱切换过程中的性能在CR ad hoc网络下均匀的主要业务。我们提出了一种新的三维离散时间马尔可夫链来描述频谱的衰落过程,并分析了非授权用户的性能。由于在真正的CR网络中,一个专用的公共控制信道是不切实际的,在我们的模型中,我们实现了一个网络协调方案,没有专用的公共控制信道是必要的。此外,在无线通信中,不能立即检测同时传输之间的冲突,并且需要重传整个冲突分组,这极大地影响了网络性能。有了这个观察,我们还考虑了在我们提出的离散时间马尔可夫链中的冲突数据包的重传。此外,除了随机信道选择方案,我们研究了不同的信道选择方案对频谱切换过程的性能的影响。此外,我们还考虑了频谱感知延迟在我们提出的马尔可夫模型,并研究其对网络性能的影响。我们验证了我们提出的马尔可夫模型对模拟和频谱切换场景中的其他参数的兴趣得到的数值结果。我们提出的分析模型可以应用于各种实际的网络场景。它也提供了新的见解的过程中的频谱衰减。目前,没有现有的分析认为,频谱切换的全面方面,我们认为在本文中。
New generation of radar systems will need to coexist with other radio frequency (RF) systems, anticipating their behavior and reacting appropriately to avoid interference. In light of this requirement, this paper designs, implements, and evaluates the performance of phase-only sequences (with constant power) for intelligent spectrum utilization using the custom built cognitive Multiple Input Multiple Output (MIMO) radar prototype. The proposed transmit waveforms avoid the frequency bands occupied by narrowband interferers or communication links, while simultaneously have a small cross-correlat…