The document proposes a low-complexity water filling algorithm to allocate subcarrier, bit, and power resources in an OFDM-based cognitive radio system with multiple primary user frequency bands. The algorithm formulates the resource allocation as a multidimensional knapsack problem to maximize the cognitive radio user's bit rate while keeping interference to primary users below thresholds. It allocates power to subcarriers using water filling to satisfy both interference and total power constraints, iterating to refine the solution if initial allocations violate constraints. The algorithm aims to provide a simple, optimal method for resource allocation in cognitive radio OFDM systems considering interference between primary and cognitive users.
Performance Analysis of Ultra Wideband Receivers for High Data Rate Wireless ...graphhoc
For high data rate ultra wideband communication system, performance comparison of Rake, MMSE and Rake-MMSE receivers is attempted in this paper. Further a detail study on Rake-MMSE time domain equalizers is carried out taking into account all the important parameters such as the effect of the number of Rake fingers and equalizer taps on the error rate performance. This receiver combats inter-symbol interference by taking advantages of both the Rake and equalizer structure. The bit error rate performances are investigated using MATLAB simulation on IEEE 802.15.3a defined UWB channel models. Simulation results show that the bit error rate probability of Rake-MMSE receiver is much better than Rake receiver and MMSE equalizer. Study on non-line of sight indoor channel models illustrates that bit error rate performance of Rake-MMSE (both LE and DFE) improves for CM3 model with smaller spread compared to CM4 channel model. It is indicated that for a MMSE equalizer operating at low to medium SNR values, the number of Rake fingers is the dominant factor to improve system performance, while at high SNR values the number of equalizer taps plays a more significant role in reducing the error rate.
Bounds on the Achievable Rates of Faded Dirty Paper Channel IJCNCJournal
Bounds on the achievable rate of a Gaussian channel in the case that the transmitter knows the
interference signal but not its fading coefficients are given. We generalize the analysis which were studied
in [1] and [4] so that their results are special cases of our analysis. We enforce our bounds by simulations
in which many numerical examples are drawn and investigated under different cases.
Multi carrier equalization by restoration of redundanc y (merry) for adaptive...IJNSA Journal
This paper proposes a new blind adaptive channel shortening approach for multi-carrier systems. The
performance of the discrete Fourier transform-DMT (DFT-DMT) system is investigated with the proposed
DST-DMT system over the standard carrier serving area (CSA) loop1. Enhanced bit rates demonstrated
and less complexity also involved by the simulation of the DST-DMT system.
n this paper channel state information is exploited for improving system performance. The per
formance parameters of
the
Multiple Input Multiple Output system is better and are even achieved using additional RF modules that are required as multi
ple
antennas are employed. To reduce the cost associated with the multiple RF modules, antenna selection
techniques can be used to
employ a smaller number of RF modules than the number of transmit antennas. The exploiting of information for complexity red
uced
antenna selection is performed for achieving high channel capacity. Simulation r
esults show
that th
e channel capacity increases in
proportion to the number of the selected antennas
Fair channel allocation and access design for cognitive ad hoc networksPolytechnique Montreal
We investigate the fair channel assignment and access design problem for cognitive radio ad hoc network in this paper. In particular, we consider a scenario where ad hoc network nodes have hardware constraints which allow them to access at most one channel at any time. We investigate a fair channel allocation problem where each node is allocated a subset of channels which are sensed and accessed periodically by their owners by using a MAC protocol. Toward this end, we analyze the complexity of the optimal brute-force search algorithm which finds the optimal solution for this NP-hard problem. We then develop low-complexity algorithms that can work efficiently with a MAC protocol algorithm, which resolves the access contention from neighboring secondary nodes. Also, we develop a throughput analytical model, which is used in the proposed channel allocation algorithm and for performance evaluation of its performance. Finally, we present extensive numerical results to demonstrate the efficacy of the proposed algorithms in achieving fair spectrum sharing among traffic flows in the network.
Tech report: Fair Channel Allocation and Access Design for Cognitive Ad Hoc N...Polytechnique Montreal
supplement to Globecom paper: L. T. Tan and L. B. Le, ``Fair Channel Allocation and Access Design for Cognitive Ad Hoc Networks,'' in 2012 IEEE Global Communications Conference (IEEE GLOBECOM 2012), Anaheim, California, USA, pp. 1162-1167, December, 2012.
Performance of MMSE Denoise Signal Using LS-MMSE TechniqueIJMER
This paper presents performance of mmse denoises signal using consistent cycle spinning (ccs) and least square (LS) techniques. In the past decade, TV denoise technique is used to reduced the noisy signal. The main drawback is the low quality signal and high MMSE signal. Presently, we
proposed the CCS-MMSE and LS-MMSE technique .The CCS-MMSE technique consists of two steps. They are wavelet based denoise and consistent cycle spinning. The wavelet denoise is powerful decorrelating effect on many signal domains. The consistent cycle spinning is used to estimation the
MMSE in the signal domain. The LS-MMSE is better estimation of MMSE signal domain compare to
CCS-MMSE.The experimental result shows the average MMSE reduction using various techniques.
Capacity Performance Analysis for Decode-and-Forward OFDMDual-Hop SystemPolytechnique Montreal
In this paper, we propose an exact analytical technique to evaluate the average capacity of a dual-hop OFDM relay system with decode-and-forward protocol in an independent and identical distribution (i.i.d.) Rayleigh fading channel. Four schemes, (no) matching “and” or “or” (no) power allocation, will be considered. First, the probability density function (pdf) for the end-to-end power channel gain for each scheme is described. Then, based on these pdf functions, we will give the expressions of the average capacity. Monte Carlo simulation results will be shown to confirm the analytical results for both the pdf functions and average capacities.
Channel and clipping level estimation for ofdm in io t –based networks a reviewIJARIIT
Internet of Things (IoT) is the idea to connect all devices to the internet. To implement such systems, we need to design
low cost and less complex transmitters and make the receiver side complex. Now days OFDM is mainly used for communication
due to its great advantages. But it faces the main problem such as PAPR due to the non-linear performance of High power
amplifiers. There are so many methods are available to reduce the effect of PAPR in OFDM transmission, among this clipping
is the simplest one. In this paper, we propose two algorithms to find the clipping level as well as the channel estimation. The
efficiency of these algorithms is evaluated by using CLRB calculation.
Adaptive Resource Allocation in MIMO-OFDM Communication Systemijsrd.com
Multiple Input and Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) system have the potential to achieve very high capacity depending on the propagation environment. The objective of this paper is the adaptive resource allocation in MIMOOFDM system using the waterfilling algorithm. Water filling solution is implemented for allocating the power in order to increase the channel capacity. The total system capacity is maximised subject to the constraints on total power, signal to noise ratio, and proportional fairness. Channel is assumed as a flat fading channel and the comparison is made for different 2x2, 2x3, 3x2 and 4x4 MIMO-OFDM systems using waterfilling algorithm with allocated power. Also in order to prove that the MIMOOFDM with waterfilling algorithm provides the best performance a comparison with various SISO - OFDM is done.
Performance Analysis of Ultra Wideband Receivers for High Data Rate Wireless ...graphhoc
For high data rate ultra wideband communication system, performance comparison of Rake, MMSE and Rake-MMSE receivers is attempted in this paper. Further a detail study on Rake-MMSE time domain equalizers is carried out taking into account all the important parameters such as the effect of the number of Rake fingers and equalizer taps on the error rate performance. This receiver combats inter-symbol interference by taking advantages of both the Rake and equalizer structure. The bit error rate performances are investigated using MATLAB simulation on IEEE 802.15.3a defined UWB channel models. Simulation results show that the bit error rate probability of Rake-MMSE receiver is much better than Rake receiver and MMSE equalizer. Study on non-line of sight indoor channel models illustrates that bit error rate performance of Rake-MMSE (both LE and DFE) improves for CM3 model with smaller spread compared to CM4 channel model. It is indicated that for a MMSE equalizer operating at low to medium SNR values, the number of Rake fingers is the dominant factor to improve system performance, while at high SNR values the number of equalizer taps plays a more significant role in reducing the error rate.
Bounds on the Achievable Rates of Faded Dirty Paper Channel IJCNCJournal
Bounds on the achievable rate of a Gaussian channel in the case that the transmitter knows the
interference signal but not its fading coefficients are given. We generalize the analysis which were studied
in [1] and [4] so that their results are special cases of our analysis. We enforce our bounds by simulations
in which many numerical examples are drawn and investigated under different cases.
Multi carrier equalization by restoration of redundanc y (merry) for adaptive...IJNSA Journal
This paper proposes a new blind adaptive channel shortening approach for multi-carrier systems. The
performance of the discrete Fourier transform-DMT (DFT-DMT) system is investigated with the proposed
DST-DMT system over the standard carrier serving area (CSA) loop1. Enhanced bit rates demonstrated
and less complexity also involved by the simulation of the DST-DMT system.
n this paper channel state information is exploited for improving system performance. The per
formance parameters of
the
Multiple Input Multiple Output system is better and are even achieved using additional RF modules that are required as multi
ple
antennas are employed. To reduce the cost associated with the multiple RF modules, antenna selection
techniques can be used to
employ a smaller number of RF modules than the number of transmit antennas. The exploiting of information for complexity red
uced
antenna selection is performed for achieving high channel capacity. Simulation r
esults show
that th
e channel capacity increases in
proportion to the number of the selected antennas
Fair channel allocation and access design for cognitive ad hoc networksPolytechnique Montreal
We investigate the fair channel assignment and access design problem for cognitive radio ad hoc network in this paper. In particular, we consider a scenario where ad hoc network nodes have hardware constraints which allow them to access at most one channel at any time. We investigate a fair channel allocation problem where each node is allocated a subset of channels which are sensed and accessed periodically by their owners by using a MAC protocol. Toward this end, we analyze the complexity of the optimal brute-force search algorithm which finds the optimal solution for this NP-hard problem. We then develop low-complexity algorithms that can work efficiently with a MAC protocol algorithm, which resolves the access contention from neighboring secondary nodes. Also, we develop a throughput analytical model, which is used in the proposed channel allocation algorithm and for performance evaluation of its performance. Finally, we present extensive numerical results to demonstrate the efficacy of the proposed algorithms in achieving fair spectrum sharing among traffic flows in the network.
Tech report: Fair Channel Allocation and Access Design for Cognitive Ad Hoc N...Polytechnique Montreal
supplement to Globecom paper: L. T. Tan and L. B. Le, ``Fair Channel Allocation and Access Design for Cognitive Ad Hoc Networks,'' in 2012 IEEE Global Communications Conference (IEEE GLOBECOM 2012), Anaheim, California, USA, pp. 1162-1167, December, 2012.
Performance of MMSE Denoise Signal Using LS-MMSE TechniqueIJMER
This paper presents performance of mmse denoises signal using consistent cycle spinning (ccs) and least square (LS) techniques. In the past decade, TV denoise technique is used to reduced the noisy signal. The main drawback is the low quality signal and high MMSE signal. Presently, we
proposed the CCS-MMSE and LS-MMSE technique .The CCS-MMSE technique consists of two steps. They are wavelet based denoise and consistent cycle spinning. The wavelet denoise is powerful decorrelating effect on many signal domains. The consistent cycle spinning is used to estimation the
MMSE in the signal domain. The LS-MMSE is better estimation of MMSE signal domain compare to
CCS-MMSE.The experimental result shows the average MMSE reduction using various techniques.
Capacity Performance Analysis for Decode-and-Forward OFDMDual-Hop SystemPolytechnique Montreal
In this paper, we propose an exact analytical technique to evaluate the average capacity of a dual-hop OFDM relay system with decode-and-forward protocol in an independent and identical distribution (i.i.d.) Rayleigh fading channel. Four schemes, (no) matching “and” or “or” (no) power allocation, will be considered. First, the probability density function (pdf) for the end-to-end power channel gain for each scheme is described. Then, based on these pdf functions, we will give the expressions of the average capacity. Monte Carlo simulation results will be shown to confirm the analytical results for both the pdf functions and average capacities.
Channel and clipping level estimation for ofdm in io t –based networks a reviewIJARIIT
Internet of Things (IoT) is the idea to connect all devices to the internet. To implement such systems, we need to design
low cost and less complex transmitters and make the receiver side complex. Now days OFDM is mainly used for communication
due to its great advantages. But it faces the main problem such as PAPR due to the non-linear performance of High power
amplifiers. There are so many methods are available to reduce the effect of PAPR in OFDM transmission, among this clipping
is the simplest one. In this paper, we propose two algorithms to find the clipping level as well as the channel estimation. The
efficiency of these algorithms is evaluated by using CLRB calculation.
Adaptive Resource Allocation in MIMO-OFDM Communication Systemijsrd.com
Multiple Input and Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) system have the potential to achieve very high capacity depending on the propagation environment. The objective of this paper is the adaptive resource allocation in MIMOOFDM system using the waterfilling algorithm. Water filling solution is implemented for allocating the power in order to increase the channel capacity. The total system capacity is maximised subject to the constraints on total power, signal to noise ratio, and proportional fairness. Channel is assumed as a flat fading channel and the comparison is made for different 2x2, 2x3, 3x2 and 4x4 MIMO-OFDM systems using waterfilling algorithm with allocated power. Also in order to prove that the MIMOOFDM with waterfilling algorithm provides the best performance a comparison with various SISO - OFDM is done.
Hybrid Time-power Switching Protocol of Energy Harvesting Bidirectional Relay...TELKOMNIKA JOURNAL
In this paper, we investigate system performance in term of throughput and ergodic capacity of the hybrid time-power switching protocol of energy harvesting bidirectional relaying network. In the first stage, the analytical expression of the system throughput and ergodic capacity of the model system is proposed and derived. In this analysis, both delay-limited and delay-tolerant transmission modes are presented and considered. After that, the effect of various system parameters on the proposed system is investigated and demonstrated by Monte-Carlo simulation. Finally, the results show that the analytical mathematical and simulated results match for all possible parameter values for both schemes.
Adaptive resources assignment in OFDM-based cognitive radio systemsIJECEIAES
Spectrum efficiency of orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems can be improved by adaptive resources allocation. In resources allocation, transmission resources such as modulation level and transmission power are adaptively assigned based on channel variations. The goal of this paper is maximize the total transmission rate of secondary user (SU). Hence, we investigate adaptive power and modulation allocation to achieve this purpose. For power allocation, we investigate optimal and conventional methods and then introduce a novel suboptimal algorithm to calculate the transmission power of each subcarrier. In addition, for adaptive modulation, we consider two kinds of modulations including multi-quadrature amplitude modulation (MQAM) and multi-phase-shift keying (MPSK). Also, simulation results are indicated the performance of our algorithm.
Outage performance of underlay cognitive radio networks over mix fading envir...IJECEIAES
In this paper, the underlay cognitive radio network over mix fading environment is presented and investigated. A cooperative cognitive system with a secondary source node S, a secondary destination node D, secondary relay node Relay, and a primary node P are considered. In this model system, we consider the mix fading environment in two scenarios as Rayleigh/ Nakagami-m and Nakagami-m/Rayleigh Fading channels. For system performance analysis, the closed-form expression of the system outage probability (OP) and the integral-formed expression of the ergodic capacity (EC) are derived in connection with the system's primary parameters. Finally, we proposed the Monte Carlo simulation for convincing the correctness of the system performance.
A QUANTITATIVE ANALYSIS OF HANDOVER TIME AT MAC LAYER FOR WIRELESS MOBILE NET...ijwmn
Extensive studies have been carried out for reducing the handover time of wireless mobile network at
medium access control (MAC) layer. However, none of them show the impact of reduced handover time
on the overall performance of wireless mobile networks. This paper presents a quantitative analysis to
show the impact of reduced handover time on the performance of wireless mobile networks. The proposed
quantitative model incorporates many critical performance parameters involve in reducing the handover
time for wireless mobile networks. In addition, we analyze the use of active scanning technique with
comparatively shorter beacon interval time in a handoff process. Our experiments verify that the active
scanning can reduce the overall handover time at MAC layer if comparatively shorter beacon intervals are
utilized for packet transmission. The performance measures adopted in this paper for experimental
verifications are network throughput under different network loads.
Pseudoperiodic waveguides with selection of spatial harmonics and modesVictor Solntsev
A principle of selection of modes and their spatial harmonics in periodic waveguides and, in particular, in spatially developed slowing systems for multibeam traveling-wave tubes (TWTs) is elaborated. The essence of the principle is in the following: varying along the length of the system its period and at least one more parameter that determines the phase shift per period, one can provide constant phase velocity of one spatial harmonic and destroy other spatial harmonics, i.e., reduce their amplitudes substantially. In this case, variations of the period may be significant, and the slowing system becomes nonuniform, or pseudoperiodic; namely, one of the spatial harmonics remains the same as in the initial periodic structure. Relationships are derived for the amplitudes of the spatial-wave harmonics, interaction coefficient, and coupling impedance of the pseudoperiodic system. The possibility of the mode selection in pseudoperiodic slowing systems when the synchronism condition is satisfied for the spatial harmonic of one mode is investigated. The efficiency of suppressing spurious spatial harmonics and modes for linear and abrupt variation of spacing is estimated. The elaborated principle of selection of spatial harmonics and modes is illustrated by an example of a two-section helical-waveguide slowing system.
MPC-EAR : Maximal Power Conserved And Energy Aware Routing in Ad hoc Networksijsrd.com
Power preservation in wireless ad hoc networks is a decisive factor as energy resources are inadequate at the electronic devices in use. Power-aware routing strategies are fundamentally route selection strategies built on accessible ad hoc routing protocols. This paper proposed a new Maximal Power Conserved And Energy Aware Routing (MPC-EAR ) topology for mobile ad hoc networks that enhances the network life span. Simulation results prove that the projected protocol has a higher performance other minimal energy usage, energy level aware and energy conserving routing protocols such as MTPR, MMECR and CMMECR.
The French Revolution, which began in 1789, was a period of radical social and political upheaval in France. It marked the decline of absolute monarchies, the rise of secular and democratic republics, and the eventual rise of Napoleon Bonaparte. This revolutionary period is crucial in understanding the transition from feudalism to modernity in Europe.
For more information, visit-www.vavaclasses.com
June 3, 2024 Anti-Semitism Letter Sent to MIT President Kornbluth and MIT Cor...Levi Shapiro
Letter from the Congress of the United States regarding Anti-Semitism sent June 3rd to MIT President Sally Kornbluth, MIT Corp Chair, Mark Gorenberg
Dear Dr. Kornbluth and Mr. Gorenberg,
The US House of Representatives is deeply concerned by ongoing and pervasive acts of antisemitic
harassment and intimidation at the Massachusetts Institute of Technology (MIT). Failing to act decisively to ensure a safe learning environment for all students would be a grave dereliction of your responsibilities as President of MIT and Chair of the MIT Corporation.
This Congress will not stand idly by and allow an environment hostile to Jewish students to persist. The House believes that your institution is in violation of Title VI of the Civil Rights Act, and the inability or
unwillingness to rectify this violation through action requires accountability.
Postsecondary education is a unique opportunity for students to learn and have their ideas and beliefs challenged. However, universities receiving hundreds of millions of federal funds annually have denied
students that opportunity and have been hijacked to become venues for the promotion of terrorism, antisemitic harassment and intimidation, unlawful encampments, and in some cases, assaults and riots.
The House of Representatives will not countenance the use of federal funds to indoctrinate students into hateful, antisemitic, anti-American supporters of terrorism. Investigations into campus antisemitism by the Committee on Education and the Workforce and the Committee on Ways and Means have been expanded into a Congress-wide probe across all relevant jurisdictions to address this national crisis. The undersigned Committees will conduct oversight into the use of federal funds at MIT and its learning environment under authorities granted to each Committee.
• The Committee on Education and the Workforce has been investigating your institution since December 7, 2023. The Committee has broad jurisdiction over postsecondary education, including its compliance with Title VI of the Civil Rights Act, campus safety concerns over disruptions to the learning environment, and the awarding of federal student aid under the Higher Education Act.
• The Committee on Oversight and Accountability is investigating the sources of funding and other support flowing to groups espousing pro-Hamas propaganda and engaged in antisemitic harassment and intimidation of students. The Committee on Oversight and Accountability is the principal oversight committee of the US House of Representatives and has broad authority to investigate “any matter” at “any time” under House Rule X.
• The Committee on Ways and Means has been investigating several universities since November 15, 2023, when the Committee held a hearing entitled From Ivory Towers to Dark Corners: Investigating the Nexus Between Antisemitism, Tax-Exempt Universities, and Terror Financing. The Committee followed the hearing with letters to those institutions on January 10, 202
Biological screening of herbal drugs: Introduction and Need for
Phyto-Pharmacological Screening, New Strategies for evaluating
Natural Products, In vitro evaluation techniques for Antioxidants, Antimicrobial and Anticancer drugs. In vivo evaluation techniques
for Anti-inflammatory, Antiulcer, Anticancer, Wound healing, Antidiabetic, Hepatoprotective, Cardio protective, Diuretics and
Antifertility, Toxicity studies as per OECD guidelines
Honest Reviews of Tim Han LMA Course Program.pptxtimhan337
Personal development courses are widely available today, with each one promising life-changing outcomes. Tim Han’s Life Mastery Achievers (LMA) Course has drawn a lot of interest. In addition to offering my frank assessment of Success Insider’s LMA Course, this piece examines the course’s effects via a variety of Tim Han LMA course reviews and Success Insider comments.
Synthetic Fiber Construction in lab .pptxPavel ( NSTU)
Synthetic fiber production is a fascinating and complex field that blends chemistry, engineering, and environmental science. By understanding these aspects, students can gain a comprehensive view of synthetic fiber production, its impact on society and the environment, and the potential for future innovations. Synthetic fibers play a crucial role in modern society, impacting various aspects of daily life, industry, and the environment. ynthetic fibers are integral to modern life, offering a range of benefits from cost-effectiveness and versatility to innovative applications and performance characteristics. While they pose environmental challenges, ongoing research and development aim to create more sustainable and eco-friendly alternatives. Understanding the importance of synthetic fibers helps in appreciating their role in the economy, industry, and daily life, while also emphasizing the need for sustainable practices and innovation.
Embracing GenAI - A Strategic ImperativePeter Windle
Artificial Intelligence (AI) technologies such as Generative AI, Image Generators and Large Language Models have had a dramatic impact on teaching, learning and assessment over the past 18 months. The most immediate threat AI posed was to Academic Integrity with Higher Education Institutes (HEIs) focusing their efforts on combating the use of GenAI in assessment. Guidelines were developed for staff and students, policies put in place too. Innovative educators have forged paths in the use of Generative AI for teaching, learning and assessments leading to pockets of transformation springing up across HEIs, often with little or no top-down guidance, support or direction.
This Gasta posits a strategic approach to integrating AI into HEIs to prepare staff, students and the curriculum for an evolving world and workplace. We will highlight the advantages of working with these technologies beyond the realm of teaching, learning and assessment by considering prompt engineering skills, industry impact, curriculum changes, and the need for staff upskilling. In contrast, not engaging strategically with Generative AI poses risks, including falling behind peers, missed opportunities and failing to ensure our graduates remain employable. The rapid evolution of AI technologies necessitates a proactive and strategic approach if we are to remain relevant.
2024.06.01 Introducing a competency framework for languag learning materials ...Sandy Millin
http://sandymillin.wordpress.com/iateflwebinar2024
Published classroom materials form the basis of syllabuses, drive teacher professional development, and have a potentially huge influence on learners, teachers and education systems. All teachers also create their own materials, whether a few sentences on a blackboard, a highly-structured fully-realised online course, or anything in between. Despite this, the knowledge and skills needed to create effective language learning materials are rarely part of teacher training, and are mostly learnt by trial and error.
Knowledge and skills frameworks, generally called competency frameworks, for ELT teachers, trainers and managers have existed for a few years now. However, until I created one for my MA dissertation, there wasn’t one drawing together what we need to know and do to be able to effectively produce language learning materials.
This webinar will introduce you to my framework, highlighting the key competencies I identified from my research. It will also show how anybody involved in language teaching (any language, not just English!), teacher training, managing schools or developing language learning materials can benefit from using the framework.
Welcome to TechSoup New Member Orientation and Q&A (May 2024).pdfTechSoup
In this webinar you will learn how your organization can access TechSoup's wide variety of product discount and donation programs. From hardware to software, we'll give you a tour of the tools available to help your nonprofit with productivity, collaboration, financial management, donor tracking, security, and more.
Instructions for Submissions thorugh G- Classroom.pptxJheel Barad
This presentation provides a briefing on how to upload submissions and documents in Google Classroom. It was prepared as part of an orientation for new Sainik School in-service teacher trainees. As a training officer, my goal is to ensure that you are comfortable and proficient with this essential tool for managing assignments and fostering student engagement.
Instructions for Submissions thorugh G- Classroom.pptx
Resource allocation in OFDM based cognitive radio system
1. Resource Allocation in an OFDM-Based Cognitive Radio System
P.Vishnu Vardhan (2011A3PS169G) and K.Gautham Reddy(2011A8PS364G)
Abstract— The problem of subcarrier, bit and
power allocation for an OFDM based cognitive
radio system in which one or more spectrum
holes exist between multiple primary user (PU)
frequency bands is studied. The cognitive radio
user is able to use any portion of the frequency
band as long as it does not Interfere unduly with
the PUs’ transmissions. We formulate the
resource allocation as a multidimensional
knapsack problem and propose a lowcomplexity, water filling algorithm to solve it.
The proposed algorithm is simple to implement
and optimal solution can be obtained by using
this method.
Index Terms —Cognitive radio, OFDM, resource
allocation, Water filling algorithm.
I. INTRODUCTION
IN many jurisdictions, there is a scarcity of unallocated
frequency bands below 6 GHz. At the same time, studies have
found that the utilization of a large portion of the allocated
(licensed) bands is very low. It has been suggested that one
promising approach to solving the spectrum shortage crisis is to
use cognitive radio (CR) technology. In a CR system, cognitive
radio users (CRUs) are allowed to use licensed bands as long as
the (licensed) primary users (PUs) are not unduly affected.
OFDM is an attractive modulation candidate for CRUs. The
subcarrier, bit and power (resource) allocation optimization
problem for OFDM has been studied
In the literature. However, for CR systems in which
the PUs do not use OFDM, the mutual interference (MI)
Between the PUs and the CRUs has to be considered.
This MI is not taken into account in most of the existing
Resource allocation algorithms for OFDM. The MI
is considered assuming that there is only one PU.
In this Letter, we study the resource allocation problem
for an OFDM-based CR system in which one or more
spectrum holes exist among the multiple PU frequency
bands. The CRU can use any portion of the band as long as
the resulting interference power is kept below the
acceptable threshold for each PU receiver. We formulate
the resource allocation optimization as a multidimensional
0-1 knapsack problem (MDKP) and propose a lowcomplexity solution.
II. SYSTEM MODEL
Consider a CR system, with bandwidth W, in which the
PUs are not active all the time at all locations. For simplicity
and clarity of explanation, we focus on the case of a single CRU
using OFDM. The proposed approach can be extended to
situations in which there may be more than one CRU.
There are M OFDM subbands available to the CRU. The
nominal bandwidth of subband m, m = {1, 2. . . M} ranges from
fc + (m − 1) Δf to fc + mΔf. The subbands (or sub channels)
are modelled in discrete-time, with the time varying gain for
sub channel m from the CRU transmitter to its receiver
denoted by√ . It is assumed that the power gains {gm} are
outcomes of independent, identically distributed (i.i.d.) random
variables (rv’s), and that there is no interference among the
subchannels. The power gains for subchannel m from the CRU
transmitter to PU l’s receiver and from PU l’s transmitter to the
CRU receiver are denoted by
and
respectively.
Suppose that there are L PUs in the system, with PU
l’s nominal bandwidth ranging from
to
The baseband power spectral density (PSD) of PU l’s
Signal is
. The maximum interference power that PU l
Can tolerate is . Since the PUs may not use OFDM, it is
necessary to consider possible MI between the CRU and the
PUs. The interference power generated by PU l to the mth
OFDM subchannel at the CRU receiver is
=∫
(
(
)
(
( )
2. The number of bits per OFDM symbol, , which can be
supported for the CRU on sub channel m is given by
(
(
)
)
is a SNR gap parameter which indicates how far
the system is operating from capacity,
is the CRU
transmit power,
is the noise power and
is the
interference from the PUs given by
where
III. THE PROPOSED RESOURCE ALLOCATION
ALGORITHM
∑
(
(
∑
≤
( )
(
)
S
)
)
)
(
,
(∑
)
) and β are the Lagrange multipliers
The Karush-Kuhn Tucker (KKT) conditions can be written as
follows
(
(
0
0
0
(∑
(∑
(2)
(3)
In (2), S is the CRU power limit, in (3)
is the interference
power injected by the CRU signal in sub band m into PU l’s
nominal band and is given by
)
(∑
β
∑
)
(
Max ∑
≤
(
( ) is the baseband PSD of the OFDM signal in
Where
sub band m when
,
number of bits per OFDM
symbol which can be
Supported for the CRU on sub channel m is given by
Where
Our objective is to maximize the overall rate achievable by the
CRU, while keeping the interference to the PUs below the
specified thresholds
{ , l = 1, 2, 3 …L}. The problem can thus be formulated as
∑
)
The problem stated above is an optimization problem we write
the Lagrangian of our above stated problem as
∑
Subject to
(
=∫
=
(
)
)
(
)=0
)
)
(
)
)
∑
By equating the above equation to zero we get
(
∑
Since
So the solution can be written as
)
(
as
)
3. (
(
For
=
(
)
∑
)
)
(
= [
)
∑
OR
(
]
otherwise
The above optimal solution for the optimization problem has a
high computational complexity so we propose a low complexity
algorithm
(
≤
We get
∑
Max ∑
)
By substituting the above equation in
∑
0
(
)
(
)
*
(
(
( )
)
)
(
∑
+
)
)
Subject to
*
∑
)
+
≤
∑
≤
S
Denotes the set of subcarriers belonging to the l Th PU band
By following the same procedure like the before problem, the
solution of the above problem is given as
=
(
∑
[
(
(
)
)
]
If the interference constraint is ignored then the above problem
will assume the water filling interpretation
=
*
(
)
+
If the total power constraint is ignored in the above problem we
get the solution as
In the above solution if
also satisfies the power
constraint,then it is our required solution. So in order to find
the optimal solution first we find
by the above method with
only interference constraint.
If the above solution also satisfies the power constraint along
with interference constraint, then the solution has been found
and is equal to the maximum power that can be allocated to
each subcarrier, i.e.
Otherwise, the available power budget should be distributed
among the subcarriers giving that the power allocated to each
subcarrier is lower than or equal to the maximum power that
can be allocated to each subcarrier
This problem can be solved by water filling algorithm
So by using the already obtained equation
=
*
We will find the water filling λ.
(
)
+
4. Calculate Tm=Γ( + )/gm for all m and arrange it in the
descending order
And Tn is the sorting index
Tsum= ΣTm for all m
If S is the CRU power limit then
λ =(Tsum+S)/no of subcarriers
n=1
while Tn> λ
Tsum = Tsum-Tn
λ =(Tsum+S)/(no of subcarriers-that particular subcarrier)
n=n+1
end
(WF)= *λ –Tm]+ for all m
Given the initial waterfilling solution, the channels that violate
the maximum power
for any particular sub channel (i.e.
(WF)> ) are determined and upper bounded with
. The
power allotted to that sub channel is subtracted from the total
transmit power S and the above algorithm is carried out for
subcarriers that did not violate the maximum power
in the
last step. This procedure is repeated until the allocated power
(W.F) doesn’t violate the maximum power
in any of the
subcarriers in the new iteration. So from this results rm is
determined for each case and the required graphs are plotted.
IV. Simulation results
The matlab code uses water filling algorithm to solve the
given problem. In the above code the interference power is
assumed constant as we are getting error with the quad
function. We are not able to obtain the graphs as there is
some error in the code which is causing the code to go for
infinite iterations that we could not rectify.
V. Conclusions
A low-complexity water filling algorithm has been
proposed for allocating resources in a OFDM-based CR
system. The algorithm maximizes the overall bit rate
achievable by the CRU, while keeping interference to PUs
within tolerable limits
REFERENCES
1) Yonghong Zhang and Cyril Leung,”Resource Allocation in an OFDM-Based
Cognitive Radio System”.
2) Musbah Shaat and Faouzi Bader,”Computationally Efficient Power Allocation
Algorithm in Multicarrier Based Cognitive Radio Networks: OFDM and FBMC
systems”