A transmitter with cognitive capability can sense talk between the other transmitter-receiver pairs. When this transmitter knows full or partial message of the others, it can choose an efficient strategy to access the transmission medium. This is referred to as cognitive radio channel. This work aims to investigate multi-tone transmission over two-user cognitive radio channels where cross-talk interference is weak. Cognitive transmitter (Ttimes1) is assumed to have full knowledge of message that is sent by the other transmitter (Ttimes2) to its corresponding receiver (Rtimes2). Channel capacity is carefully analyzed for frequency-selective scenarios. Efficient power-allocation strategies at Ttimes1 are investigated for various wireless environments. It is shown that Ttimes1 can find an efficient resource-accessing strategy if the channel gain of Ttimes1-Rtimes1 (the corresponding receiver) link is larger than the channel gain of Ttimes2-Rtimes2 link. In this case, the cognitive transmitter Ttimes1 can offer better performance by employing equal power allocation approach. Otherwise, it is not worthy for Ttimes1 to access transmission medium of Ttimes2-Rtimes2 link.
Flexibly supporting multiple services, each with different communication requirements and frame structure, has been identified as one of the most significant and promising characteristics of next generation and beyond wireless communication systems. However, integrating multiple frame structures with different subcarrier spacing in one radio carrier may result in significant inter-service-band-interference (ISBI). In this paper, a framework for multi-service (MS) systems is established based on a subband filtered multi-carrier system. The subband filtering implementations and both asynchronous and generalized synchronous (GS) MS subband filtered multi-carrier (SFMC) systems have been proposed. Based on the GS-MS-SFMC system, the system model with ISBI is derived and a number of properties on ISBI are given. In addition, low-complexity ISBI cancelation algorithms are proposed by precoding the information symbols at the transmitter. For asynchronous MS-SFMC system in the presence of transceiver imperfections, including carrier frequency offset, timing offset, and phase noise, a complete analytical system model is established in terms of desired signal, inter-symbol-interference, inter-carrier-interference, ISBI, and noise. Thereafter, new channel equalization algorithms are proposed by considering the errors and imperfections. Numerical analysis shows that the analytical results match the simulation results, and the proposed ISBI cancelation and equalization algorithms can significantly improve the system performance in comparison with the existing algorithms.
This paper presents a comprehensive survey of the literature on self-interference management schemes required to achieve a single frequency full duplex (FD) communication in wireless communication networks. A single frequency FD system often referred to as in-band FD system has emerged as an interesting solution for the next generation mobile networks, where the scarcity of available radio spectrum is an important issue. Although studies on the mitigation of self-interference have been documented in the literature, this is the first holistic attempt at presenting not just the various techniques available for handling self-interference that arises when an FD device is enabled, as a survey, but it also discusses other system impairments that significantly affect the self-interference management of the system, and not only in terrestrial systems, but also on satellite communication systems. The survey provides a taxonomy of selfinterference management schemes and shows by means of comparisons the strengths and limitations of various self-interference management schemes. It also quantifies the amount of self-interference cancellation required for different access schemes from the first generation to the candidate fifth generation of mobile cellular systems. Importantly, the survey summarizes the lessons learnt, identifies and presents open research questions and key research areas for the future. This paper is intended to be a guide and take off point for further work on self-interference management in order to achieve FD transmission in mobile networks, including heterogeneous cellular networks, which is undeniably the network of the future wireless systems.
Managing and maintaining network connectivity in a mobile ad-hoc network (MANET) is known to consume bandwidth and energy at the mobile nodes. Traditional mechanisms require that stations periodically monitor the wireless channel, in order to determine available paths to route incoming packets. Aiming to alleviate the problem of energy consumption and high control overhead, this paper adopts a new approach to passive neighbourhood detection, based on Network Coding. Specifically, ad-hoc stations examine the coding vectors and subspaces of incoming network-coded packets to extract information about the subspaces spanned by these vectors, enabling them to passively discover new neighbours. The new discovery mechanism is incorporated into the well-known dynamic MANET on-demand (DYMO) ad-hoc routing protocol and the features of the combined scheme are discussed, towards assessing the potential advantages of the proposed approach, particularly with respect to energy efficiency.
Wireless networks are evolving into a unique heterogeneous scenario. Moreover, mobile terminals with multiple wireless interfaces have the ability to roam between different access networks. Allowing seamless and efficient vertical handoffs is becoming a key requirement for future wireless environments. We discuss the application of recent kind of network codes called batched sparse (BATS) codes on HARD vertical handoffs between LTE and IEEE 802.11n to reduce packet loss and to increase performances. The first part of our analysis demonstrates a reduction of packet loss by applying network coding. However, the second part shows that the redundancy of the codes increases the energy per bit consumed by mobile terminals.
An improved signal quality estimation algorithm, applicable to CDMA-based mobile communication systems, is proposed. The algorithm estimates the Eb/N0 at the receiver end by operating on the despread symbols of the received in-phase (I) and quadrature (Q) channels. The improvement in performance is obtained by the addition of a smoothing filter to the existing algorithm. The performance of the algorithm is compared initially in a Gaussian channel and then in a time-varying channel that emulates fast fading.
It has been claimed that filter bank multicarrier (FBMC) systems suffer from negligible performance loss caused by moderate dispersive channels in the absence of guard time protection between symbols. However, a theoretical and systematic explanation/analysis for the statement is missing in the literature to date. In this paper, based on one-tap minimum mean square error (MMSE) and zero-forcing (ZF) channel equalizations, the impact of doubly dispersive channel on the performance of FBMC systems is analyzed in terms of mean square error of received symbols. Based on this analytical framework, we prove that the circular convolution property between symbols and the corresponding channel coefficients in the frequency domain holds loosely with a set of inaccuracies. To facilitate analysis, we first model the FBMC system in a vector/matrix form and derive the estimated symbols as a sum of desired signal, noise, intersymbol interference (ISI), intercarrier interference (ICI), interblock interference (IBI), and estimation bias in the MMSE equalizer. Those terms are derived one-by-one and expressed as a function of channel parameters. The numerical results reveal that under harsh channel conditions, e.g., with large Doppler spread or channel delay spread, the FBMC system performance may be severely deteriorated and error floor will occur.
The term space wave refers to a wave that is propagating through an open medium with a diverging wavefront as it moves away from the source. The term guided wave denotes a variety of wave configurations that are being carried by a closed/open/partially open structure [1]. A guided wave may also be known as a bounded wave, which is a term inspired by its propagation mechanism, where a traveling wave is bounded by two dissimilar mediums with different electromagnetic (EM) characteristics; the wave propagates along the interface and decays exponentially to the surrounding mediums.
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