This document provides an overview of capacity results for single-user and multi-user MIMO channels under various assumptions about channel knowledge and correlation. It discusses that capacity gains from MIMO depend heavily on channel knowledge, SNR, and correlation between antenna gains. Key results covered include ergodic and outage capacity for single-user MIMO channels, and capacity regions for MIMO broadcast and multiple access channels with perfect channel knowledge. The duality between these multi-user channels is also summarized.
A STUDY ON QUANTITATIVE PARAMETERS OF SPECTRUM HANDOFF IN COGNITIVE RADIO NET...ijwmn
The innovation of wireless technologies requires dynamic allocation of spectrum band in an efficient
manner. This has been achieved by Cognitive Radio (CR) networks which allow unlicensed users to make
use of free licensed spectrum, when the licensed users are kept away from that spectrum. The cognitive
radio makes decision, switching from primary user to secondary user and vice-versa, based on its built-in
interference engine. It allows secondary users to makes use of a channel based on its availability i.e. on the
absence of the primary user and they should vacate the channel once the primary user re-enters and
continue their communication on another available channel and this process in the cognitive radio is
known as spectrum mobility. The main objective of spectrum mobility is that, there is no interruption
caused due to the channel occupied by secondary users and maintains a good quality of service. In order to
achieve better spectrum mobility, it is mandatory to choose an effective spectrum handoff strategy with the
capability of predicting spectrum mobility. The handoff strategy with its parameters and its impact is an
important concept in spectrum mobility but fairly explored. In this paper an empirical study on quantitative
parameters involved in spectrum mobility prediction are discussed in detail. These parameters are studied
extensively because they play a vital role in the spectrum handoff process moreover the impact of these
parameters in various handoff methods can be used to predict the effectiveness of the system.
Performance analysis of multilayer multicast MANET CRN based on steiner minim...TELKOMNIKA JOURNAL
In this study, the multicast mobile ad hoc (MANET) CRN has been developed, which involves multi-hop and multilayer consideration and Steiner minimal tree (SMT) algorithm is employed as the router protocol. To enhance the network performance with regards to throughput and packet delivery rate (PDR), as channel assignment scheme, the probability of success (POS) is employed that accounts for the channel availability and the time needed for transmission when selecting the best channel from the numerous available channels for data transmission from the source to all destinations nodes effectively. Within Rayleigh fading channels under various network parameters, a comparison is done for the performance of SMT multicast (MANET) CRN with POS scheme versus maximum data rate (MDR), maximum average spectrum availability (MASA) and random channel assignment schemes. Based on the simulation results, the SMT multicast (MANET) CRN with POS scheme was seen to demonstrate the best performance versus other schemes. Also, the results proved that the throughput and PDR performance are improved as the number the primary channels and the channel’s bandwidth increased while dropped as the value of packet size D increased. The network’s performance grew with rise in the value of idle probability (푃퐼) since the primary user’s (PU) traffic load is low when the value of 푃퐼 is high.
Resource Allocation in MIMO – OFDM Communication System under Signal Strength...Kumar Goud
Abstract: - Multiple Inputs and Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) system have the potential to attain high capability on the propagation setting. The aim of this paper is that the adaptive resource allocation in MIMO-OFDM system uses the water filling formula. Water filling answer is enforced for allocating the ability so as to extend the data rate. The overall system capability is maximised subject to the constraints on total power, signal to noise quantitative relation, and proportionality. Channel is assumed as a flat attenuation channel and therefore the comparison is created for various 2×2, 2×3, 3×2 and 4×4 MIMO-OFDM systems and water filling formula with allotted power. Supported the capability contribution from the relaying terminal, a brand new parameter referred to as cooperation constant is introduced as an operate of the relaying sub channel. This parameter is employed to switch the target parameter of the subcarrier allocation procedure. Fairness-oriented [Fading Channel] and throughput-oriented [Near finish Channel] algorithms square measure elite from the literature to check the planned technique. Each algorithms square measure changed to use the mean of cooperation constant within the objective parameter of the subcarrier allocation procedure and shown to own a much better total turnout with none sacrifice.
Keywords - MIMO-OFDM; Water filling Algorithm; Subcarrier Resource Allocation
A CRITICAL REVIEW OF THE ROUTING PROTOCOLS FOR COGNITIVE RADIO NETWORKS AND A...cscpconf
We present a critical review and analysis of different categories of routing protocols for cognitive radio networks. We first classify the available solutions to two broad categories: those
based on full spectrum knowledge (typically used to establish performance benchmarks) and those based on local spectrum knowledge (used for real-time implementation). The full spectrum knowledge based routing solutions are analyzed from a graph-theoretic point of view, and we review the layered graph, edge coloring and conflict graph models. We classify the various local spectrum knowledge based routing protocols into the following five categories: Minimum power, Minimum delay, Maximum throughput, Geographic and Class-based routing. A total of 25 routing protocols proposed for cognitive radio networks have been reviewed. We discuss the working principle and analyze the pros and cons of the routing protocols. Finally, we propose an idea of a load balancing-based local spectrum knowledge-based routing protocol for cognitive radio ad hoc networks.
A STUDY ON QUANTITATIVE PARAMETERS OF SPECTRUM HANDOFF IN COGNITIVE RADIO NET...ijwmn
The innovation of wireless technologies requires dynamic allocation of spectrum band in an efficient
manner. This has been achieved by Cognitive Radio (CR) networks which allow unlicensed users to make
use of free licensed spectrum, when the licensed users are kept away from that spectrum. The cognitive
radio makes decision, switching from primary user to secondary user and vice-versa, based on its built-in
interference engine. It allows secondary users to makes use of a channel based on its availability i.e. on the
absence of the primary user and they should vacate the channel once the primary user re-enters and
continue their communication on another available channel and this process in the cognitive radio is
known as spectrum mobility. The main objective of spectrum mobility is that, there is no interruption
caused due to the channel occupied by secondary users and maintains a good quality of service. In order to
achieve better spectrum mobility, it is mandatory to choose an effective spectrum handoff strategy with the
capability of predicting spectrum mobility. The handoff strategy with its parameters and its impact is an
important concept in spectrum mobility but fairly explored. In this paper an empirical study on quantitative
parameters involved in spectrum mobility prediction are discussed in detail. These parameters are studied
extensively because they play a vital role in the spectrum handoff process moreover the impact of these
parameters in various handoff methods can be used to predict the effectiveness of the system.
Performance analysis of multilayer multicast MANET CRN based on steiner minim...TELKOMNIKA JOURNAL
In this study, the multicast mobile ad hoc (MANET) CRN has been developed, which involves multi-hop and multilayer consideration and Steiner minimal tree (SMT) algorithm is employed as the router protocol. To enhance the network performance with regards to throughput and packet delivery rate (PDR), as channel assignment scheme, the probability of success (POS) is employed that accounts for the channel availability and the time needed for transmission when selecting the best channel from the numerous available channels for data transmission from the source to all destinations nodes effectively. Within Rayleigh fading channels under various network parameters, a comparison is done for the performance of SMT multicast (MANET) CRN with POS scheme versus maximum data rate (MDR), maximum average spectrum availability (MASA) and random channel assignment schemes. Based on the simulation results, the SMT multicast (MANET) CRN with POS scheme was seen to demonstrate the best performance versus other schemes. Also, the results proved that the throughput and PDR performance are improved as the number the primary channels and the channel’s bandwidth increased while dropped as the value of packet size D increased. The network’s performance grew with rise in the value of idle probability (푃퐼) since the primary user’s (PU) traffic load is low when the value of 푃퐼 is high.
Resource Allocation in MIMO – OFDM Communication System under Signal Strength...Kumar Goud
Abstract: - Multiple Inputs and Multiple Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) system have the potential to attain high capability on the propagation setting. The aim of this paper is that the adaptive resource allocation in MIMO-OFDM system uses the water filling formula. Water filling answer is enforced for allocating the ability so as to extend the data rate. The overall system capability is maximised subject to the constraints on total power, signal to noise quantitative relation, and proportionality. Channel is assumed as a flat attenuation channel and therefore the comparison is created for various 2×2, 2×3, 3×2 and 4×4 MIMO-OFDM systems and water filling formula with allotted power. Supported the capability contribution from the relaying terminal, a brand new parameter referred to as cooperation constant is introduced as an operate of the relaying sub channel. This parameter is employed to switch the target parameter of the subcarrier allocation procedure. Fairness-oriented [Fading Channel] and throughput-oriented [Near finish Channel] algorithms square measure elite from the literature to check the planned technique. Each algorithms square measure changed to use the mean of cooperation constant within the objective parameter of the subcarrier allocation procedure and shown to own a much better total turnout with none sacrifice.
Keywords - MIMO-OFDM; Water filling Algorithm; Subcarrier Resource Allocation
A CRITICAL REVIEW OF THE ROUTING PROTOCOLS FOR COGNITIVE RADIO NETWORKS AND A...cscpconf
We present a critical review and analysis of different categories of routing protocols for cognitive radio networks. We first classify the available solutions to two broad categories: those
based on full spectrum knowledge (typically used to establish performance benchmarks) and those based on local spectrum knowledge (used for real-time implementation). The full spectrum knowledge based routing solutions are analyzed from a graph-theoretic point of view, and we review the layered graph, edge coloring and conflict graph models. We classify the various local spectrum knowledge based routing protocols into the following five categories: Minimum power, Minimum delay, Maximum throughput, Geographic and Class-based routing. A total of 25 routing protocols proposed for cognitive radio networks have been reviewed. We discuss the working principle and analyze the pros and cons of the routing protocols. Finally, we propose an idea of a load balancing-based local spectrum knowledge-based routing protocol for cognitive radio ad hoc networks.
Various Common Control Channel Assignment Schemes in CRNs: A Survey .........................................1
Jagsir Singh, Inderdeep Kaur Aulakh and Roopali Garg
Framework for Threat Modelling for a Power Utility: Case of Zimbabwe Power Utility Company.......... 8
Samuel Musungwini, Gilbert Mahlangu, Beauty Mugoniwa, and Samuel Simbarashe Furusa
Enhanced-bandwidth Compact Printed Inverted F Antenna Suitable for LTE/GSM Mobile Phone ....... 24
S. Jesse Jackson and T. Thomas
Implementation of e-Government Services using Java Technologies: A Methodological Guide in
Improving an e-Police Management System in Zimbabwe ...................................................................... 32
Mahlangu Gilbert, Chikonye Musafare, Furusa Samuel Simbarashe and Mugoniwa Beauty
Onto Tagger: Ontology Focused Image Tagging System Incorporating Semantic Deviation Computing
and Strategic Set Expansion ...................................................................................................................... 44
Gerard Deepak and Sheeba Priyadarshini J
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
LARGE-SCALE MULTI-USER MIMO APPROACH FOR WIRELESS BACKHAUL BASED HETNETScsandit
In this paper, we consider the optimization of wireless capacity-limited backhaul links in future heterogeneous networks (HetNets). We assume that the HetNet is formed with one macro-cell base station (MBS), which is associated with multiple small-cell base stations (SBSs). It is also assumed both the MBS and the SBSs are equipped with massive arrays, while all mobiles users (macro-cell and small-cell users) have single antenna. For the backhaul links, we propose to use a capacity-aware beamforming scheme at the SBSs and MRC at the MBS. Using particle swarm optimization (PSO), each SBS seeks the optimal transmit weight vectors that maximize the backhaul uplink capacity and the access uplinks signal-to-interference plus noise ratio (SINR). The performance evaluation in terms of the symbol error rate (SER) and the ergodic system capacity shows that the proposed capacity-aware backhaul link scheme achieves similar or better performance than traditional wireless backhaul links and requires considerably less computational complexity.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
An approach to control inter cellular interference using load matrix in multi...eSAT Journals
Abstract
This paper deals with reduction of inter cellular interference in Multi-carrier communication systems. In the past, Load Matrix(LM) is proposed to allocate power to different users in a network based upon Signal to noise plus interference ratio (SNIR) so as to reduce inter cellular interference and is observed for single carrier systems. In Multi carrier systems the SNIR is affected distinctly in each carrier thus a single SNIR for power allocation is not optimal. In this paper, to obtain the optimization of power allocation in Multi-Carrier system, Load Matrix coding with bifurcated SNIR (LM-BFSNIR) is proposed. Using this approach it is observed that inter cellular interference is reduced better when compared to a single carrier system evaluated over a 3GPP-LTE standard.
Keywords−Power allocation, Inter cellular interference, Multi-Carrier mobile Communication system.
Routing in Cognitive Radio Networks - A SurveyIJERA Editor
Cognitive Radio Networks (CRNs) have been emerged as a revolutionary solution to migrate the spectrum
scarcity problem in wireless networks. Due to increasing demand for additional spectrum resources, CRNs have
been receiving significant research to solve issues related with spectrum underutilization. This technology
brings efficient spectrum usage and effective interference avoidance, and also brings new challenges to routing
in multi-hop Cognitive Radio Networks. In CRN, unlicensed users or secondary users are able to use
underutilized licensed channels, but they have to leave the channel if any interference is caused to the primary or
licensed users. So CR technology allows sharing of licensed spectrum band in opportunistic and non-interfering
manner. Different routing protocols have been proposed recently based on different design goals under different
assumptions.
Performance Analysis of Ultra Wideband Communication SystemEditor IJMTER
Ultra-Wideband (UWB) is a radio transmission scheme that uses extremely low power
pulses of radio energy spread across a wide spectrum of frequencies. UWB has several advantages
over conventional continuous wave radio communications including potential support for high data
rates, robustness to multipath interference and fading. The paper covers Ultra Wide-Band
technology. General description, Challenges, various modulation schemes such as OOK, PAM,
PPM, and BPSK under specified Ultra Wide Band regimes: low Power spectral density, large
spreading ratio and a highly dispersive channel. The capacity and BER performance of a single user
ultra wideband communication is investigated for various modulation schemes and coded, uncoded
methods also simulated. Fading channel like Ricean and Rayleigh are compared. Channelized digital
receiver concept is discussed.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Shared Spectrum Throughput for Secondary UsersCSCJournals
The throughput performance of secondary users sharing radio spectrum with a licensed primary user is analyzed in this work. An asynchronous transmission, sensing and backoff protocol is proposed for the secondary user and modeled as a six state Markov process. The model parameters are derived as a function of the duty cycle and average duration that the channel is unoccupied by the primary user. The secondary user parameters include its continuous transmission duration or packet size and its backoff window size. The model results show that the probabilities of the secondary user being in the transmit state are relatively invariant to the duty cycle compared to the probability of being in the backoff state, particularly at low to moderate secondary packet sizes. The secondary user throughput is expressed as a function of the aforementioned parameters and shown to change significantly with duty cycle and secondary packet sizes. It is found that at very low duty cycles, the throughput variation is insensitive to backoff duration being random or fixed. The proposed transmission and sensing method is also shown to outperform a periodic sensing protocol. The regions of the parameter space wherein the backoff and retransmit probabilities of the secondary user are bounded by specified performance metrics are derived. The sensitivity of the throughput in the presence of a cooperative and non- cooperative secondary user is also investigated.
IMPLEMENTATION OF LINEAR DETECTION TECHNIQUES TO OVERCOME CHANNEL EFFECTS IN ...IJCI JOURNAL
Spatial diversity technique enables improvement in quality and reliability of wireless link. Antenna
diversity along with understanding effects of channel on transmitted signal and methods to overcome the
channel impairment plays an important role in wireless communication where sharing of channel occurs
between users. In this paper single input single output system (SISO) is compared with multiple input
multiple output system (MIMO) in terms of bit error rate performance. Bit error rate performance is also
evaluated for MIMO with least squares (LS) and Minimum mean square error (MMSE) linear detection.
Further analysis and simulation is done to understand the effect of channel imperfections on BER.
Improved Cell Coverage in Hilly Areas using Cellular AntennasEswar Publications
This paper proposes an improved configuration of Cellular Antennas for terrains like hills where network coverage is poor and a number of black spots are very high. The proposed solution delivers efficient and much robust antenna structure which provides better network coverage by using 90-degree sector antennas. The radio spectrum of the 90-degree sector antenna is also shown to give the idea of cell coverage in order to build aseamless network in the region.This paper also proposes different channel allocation schemes that can be used with the proposed antenna configuration to deliver better network coverage and low call dropping probability.
This is achieved by analyzing the terrain of the region and also the cellular traffic in the region. In areas where network traffic is almost constant or have low population, strategies like fixed channel allocation can be used effectively and efficiently. While in the areas where traffic is unpredictable or is subject to regional festivals or tourism, channel strategies like dynamic channel allocation are very useful to fulfill the demand of the overall network. The simulations and validations for the proposed methodology are done using MATLAB.
Mobile Primary User in Cognitive Radio State of the Arts and Recent Advancesjosephjonse
The processing of primary user mobility with static or mobile secondary user in the context of cognitive radio (CR) has recently been the subject of several studies and discussions all over the world. These studies are seeking to broaden the horizons of CR implementation beyond the formalism described in the diverse existing standards. The mobility of primary users is likely to reduce the overall performance of the Cognitive Radio Network (CRN) and affects the different phases of the cognitive cycle. Said mobility alters the network’s topology, the channel’s availability, and affects spectrum sensing. This makes any endeavor aiming to implement CR technology complicated. This paper is devoted to the analysis and discussion of the scientific literature that has addressed the issue of the primary user’s mobility.
Various Common Control Channel Assignment Schemes in CRNs: A Survey .........................................1
Jagsir Singh, Inderdeep Kaur Aulakh and Roopali Garg
Framework for Threat Modelling for a Power Utility: Case of Zimbabwe Power Utility Company.......... 8
Samuel Musungwini, Gilbert Mahlangu, Beauty Mugoniwa, and Samuel Simbarashe Furusa
Enhanced-bandwidth Compact Printed Inverted F Antenna Suitable for LTE/GSM Mobile Phone ....... 24
S. Jesse Jackson and T. Thomas
Implementation of e-Government Services using Java Technologies: A Methodological Guide in
Improving an e-Police Management System in Zimbabwe ...................................................................... 32
Mahlangu Gilbert, Chikonye Musafare, Furusa Samuel Simbarashe and Mugoniwa Beauty
Onto Tagger: Ontology Focused Image Tagging System Incorporating Semantic Deviation Computing
and Strategic Set Expansion ...................................................................................................................... 44
Gerard Deepak and Sheeba Priyadarshini J
IJRET : International Journal of Research in Engineering and Technology is an international peer reviewed, online journal published by eSAT Publishing House for the enhancement of research in various disciplines of Engineering and Technology. The aim and scope of the journal is to provide an academic medium and an important reference for the advancement and dissemination of research results that support high-level learning, teaching and research in the fields of Engineering and Technology. We bring together Scientists, Academician, Field Engineers, Scholars and Students of related fields of Engineering and Technology.
LARGE-SCALE MULTI-USER MIMO APPROACH FOR WIRELESS BACKHAUL BASED HETNETScsandit
In this paper, we consider the optimization of wireless capacity-limited backhaul links in future heterogeneous networks (HetNets). We assume that the HetNet is formed with one macro-cell base station (MBS), which is associated with multiple small-cell base stations (SBSs). It is also assumed both the MBS and the SBSs are equipped with massive arrays, while all mobiles users (macro-cell and small-cell users) have single antenna. For the backhaul links, we propose to use a capacity-aware beamforming scheme at the SBSs and MRC at the MBS. Using particle swarm optimization (PSO), each SBS seeks the optimal transmit weight vectors that maximize the backhaul uplink capacity and the access uplinks signal-to-interference plus noise ratio (SINR). The performance evaluation in terms of the symbol error rate (SER) and the ergodic system capacity shows that the proposed capacity-aware backhaul link scheme achieves similar or better performance than traditional wireless backhaul links and requires considerably less computational complexity.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
An approach to control inter cellular interference using load matrix in multi...eSAT Journals
Abstract
This paper deals with reduction of inter cellular interference in Multi-carrier communication systems. In the past, Load Matrix(LM) is proposed to allocate power to different users in a network based upon Signal to noise plus interference ratio (SNIR) so as to reduce inter cellular interference and is observed for single carrier systems. In Multi carrier systems the SNIR is affected distinctly in each carrier thus a single SNIR for power allocation is not optimal. In this paper, to obtain the optimization of power allocation in Multi-Carrier system, Load Matrix coding with bifurcated SNIR (LM-BFSNIR) is proposed. Using this approach it is observed that inter cellular interference is reduced better when compared to a single carrier system evaluated over a 3GPP-LTE standard.
Keywords−Power allocation, Inter cellular interference, Multi-Carrier mobile Communication system.
Routing in Cognitive Radio Networks - A SurveyIJERA Editor
Cognitive Radio Networks (CRNs) have been emerged as a revolutionary solution to migrate the spectrum
scarcity problem in wireless networks. Due to increasing demand for additional spectrum resources, CRNs have
been receiving significant research to solve issues related with spectrum underutilization. This technology
brings efficient spectrum usage and effective interference avoidance, and also brings new challenges to routing
in multi-hop Cognitive Radio Networks. In CRN, unlicensed users or secondary users are able to use
underutilized licensed channels, but they have to leave the channel if any interference is caused to the primary or
licensed users. So CR technology allows sharing of licensed spectrum band in opportunistic and non-interfering
manner. Different routing protocols have been proposed recently based on different design goals under different
assumptions.
Performance Analysis of Ultra Wideband Communication SystemEditor IJMTER
Ultra-Wideband (UWB) is a radio transmission scheme that uses extremely low power
pulses of radio energy spread across a wide spectrum of frequencies. UWB has several advantages
over conventional continuous wave radio communications including potential support for high data
rates, robustness to multipath interference and fading. The paper covers Ultra Wide-Band
technology. General description, Challenges, various modulation schemes such as OOK, PAM,
PPM, and BPSK under specified Ultra Wide Band regimes: low Power spectral density, large
spreading ratio and a highly dispersive channel. The capacity and BER performance of a single user
ultra wideband communication is investigated for various modulation schemes and coded, uncoded
methods also simulated. Fading channel like Ricean and Rayleigh are compared. Channelized digital
receiver concept is discussed.
IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com
Shared Spectrum Throughput for Secondary UsersCSCJournals
The throughput performance of secondary users sharing radio spectrum with a licensed primary user is analyzed in this work. An asynchronous transmission, sensing and backoff protocol is proposed for the secondary user and modeled as a six state Markov process. The model parameters are derived as a function of the duty cycle and average duration that the channel is unoccupied by the primary user. The secondary user parameters include its continuous transmission duration or packet size and its backoff window size. The model results show that the probabilities of the secondary user being in the transmit state are relatively invariant to the duty cycle compared to the probability of being in the backoff state, particularly at low to moderate secondary packet sizes. The secondary user throughput is expressed as a function of the aforementioned parameters and shown to change significantly with duty cycle and secondary packet sizes. It is found that at very low duty cycles, the throughput variation is insensitive to backoff duration being random or fixed. The proposed transmission and sensing method is also shown to outperform a periodic sensing protocol. The regions of the parameter space wherein the backoff and retransmit probabilities of the secondary user are bounded by specified performance metrics are derived. The sensitivity of the throughput in the presence of a cooperative and non- cooperative secondary user is also investigated.
IMPLEMENTATION OF LINEAR DETECTION TECHNIQUES TO OVERCOME CHANNEL EFFECTS IN ...IJCI JOURNAL
Spatial diversity technique enables improvement in quality and reliability of wireless link. Antenna
diversity along with understanding effects of channel on transmitted signal and methods to overcome the
channel impairment plays an important role in wireless communication where sharing of channel occurs
between users. In this paper single input single output system (SISO) is compared with multiple input
multiple output system (MIMO) in terms of bit error rate performance. Bit error rate performance is also
evaluated for MIMO with least squares (LS) and Minimum mean square error (MMSE) linear detection.
Further analysis and simulation is done to understand the effect of channel imperfections on BER.
Improved Cell Coverage in Hilly Areas using Cellular AntennasEswar Publications
This paper proposes an improved configuration of Cellular Antennas for terrains like hills where network coverage is poor and a number of black spots are very high. The proposed solution delivers efficient and much robust antenna structure which provides better network coverage by using 90-degree sector antennas. The radio spectrum of the 90-degree sector antenna is also shown to give the idea of cell coverage in order to build aseamless network in the region.This paper also proposes different channel allocation schemes that can be used with the proposed antenna configuration to deliver better network coverage and low call dropping probability.
This is achieved by analyzing the terrain of the region and also the cellular traffic in the region. In areas where network traffic is almost constant or have low population, strategies like fixed channel allocation can be used effectively and efficiently. While in the areas where traffic is unpredictable or is subject to regional festivals or tourism, channel strategies like dynamic channel allocation are very useful to fulfill the demand of the overall network. The simulations and validations for the proposed methodology are done using MATLAB.
Mobile Primary User in Cognitive Radio State of the Arts and Recent Advancesjosephjonse
The processing of primary user mobility with static or mobile secondary user in the context of cognitive radio (CR) has recently been the subject of several studies and discussions all over the world. These studies are seeking to broaden the horizons of CR implementation beyond the formalism described in the diverse existing standards. The mobility of primary users is likely to reduce the overall performance of the Cognitive Radio Network (CRN) and affects the different phases of the cognitive cycle. Said mobility alters the network’s topology, the channel’s availability, and affects spectrum sensing. This makes any endeavor aiming to implement CR technology complicated. This paper is devoted to the analysis and discussion of the scientific literature that has addressed the issue of the primary user’s mobility.
Massive MIMO (also known as “Large-Scale Antenna Systems”, “Very Large MIMO”, “Hyper MIMO”, “Full-Dimension MIMO” and “ARGOS”) makes a clean break with current practice through the use of a large excess of service-antennas over active terminals and time division duplex operation. Extra antennas help by focusing energy into ever-smaller regions of space to bring huge improvements in throughput and radiated energy efficiency. Other benefits of massive MIMO include the extensive use of inexpensive low-power components, reduced latency, simplification of the media access control (MAC) layer, and robustness to intentional jamming. The anticipated throughput depend on the propagation environment providing asymptotically orthogonal channels to the terminals, but so far experiments have not disclosed any limitations in this regard. While massive MIMO renders many traditional research problems irrelevant, it uncovers entirely new problems that urgently need attention: the challenge of making many low-cost low-precision components that work effectively together, acquisition and synchronization for newly-joined terminals, the exploitation of extra degrees of freedom provided by the excess of service-antennas, reducing internal power consumption to achieve total energy efficiency reductions, and finding new deployment scenarios.
A New Transmission Scheme for MIMO – OFDMijsrd.com
This contribution introduces a new transmission scheme for multiple-input multiple-output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems. The new scheme is efficient and suitable especially for symmetric channels such as the link between two base stations or between two antennas on radio beam transmission. This survey Paper presents the performance analysis of V-BLAST based multiple inputs multiple output orthogonal frequency division multiplexing (MIMO-OFDM) system with respect to bit error rate per signal to noise ratio (BER/SNR) for various detection techniques. A 2X2 MIMO-OFDM system is used for the performance evaluation. The simulation results shows that the performance of V-BLAST based detection techniques is much better than the conventional methods. Alamouti Space Time Block Code (STBC) scheme is used with orthogonal designs over multiple antennas which showed simulated results are identical to expected theoretical results. With this technique both Bit Error Rate (BER) and maximum diversity gain are achieved by increasing number of antennas on either side. This scheme is efficient in all the applications where system capacity is limited by multipath fading.
Design and analysis of mimo system for uwb communicationijwmn
Multiple transmit and receive antennas are used MIMO system. The system creates parallel MIMO
subchannels to transmit independent streams of data under the appropriate channel conditions. Similarly,
Ultrawideband (UWB) communication has attracted great interest for various applications in recent days.
Spatially multiplexed (SM) multiple-input multiple-output (MIMO) systems gains the spectral efficiency as
well as high data rates without consuming additional power, bandwidth or time slots. In this paper, we
extend the concept of MIMO to UWB systems. The correlated channel for such purpose is considered and
the performance has been analyzed for spatial multiplexing SM-UWB-MIMO system which is required for
estimation. The system performance substantially degrades in the presence of high values of spatial
correlation. To avoid the degradation of such system, it has been designed for virtual UWB-MIMO Time
Reversal (TR) system, so that it is not affected by the transmit correlation. Another novel method to reduce
the effect of correlation has been chosen by taking the Eigen value of the channel matrix for the
computation of the system performance. The result shows its performance.
Channel feedback scheduling for wireless communicationseSAT Journals
Abstract Opportunistic scheduling can significantly improve wireless network performance by exploiting the underlying channel condition. There has been a lot of work on opportunistic scheduling, but the problem of finding the right feedback mechanism to convey channel information has largely been untouched. In emerging multichannel systems, the per-channel feedback induces a substantial amount of feedback overhead and requires high computational complexity. To reduce the feedback overhead, we consider an opportunistic feedback strategy that activates the channel feedback opportunistically according to the channel condition. Then, we combine the opportunistic feedback with the best-n channel feedback scheme where a mobile user chooses the best n channels and transfers this information to the base station. We analyze the throughput and the amount of channel feedback information for proportionally fair opportunistic scheduling under Rayleigh fading i.i.d. channels. The numerical results confirm that our partial feedback schemes achieve a remarkable reduction in the amount of feedback information without significant throughput degradation, thereby saving the scarce wireless bandwidth and limited battery power.
EFFICIENT ANALYSIS OF THE ERGODIC CAPACITY OF COOPERATIVE NON-REGENERATIVE RE...ijwmn
In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the
cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight
approximate moment generating function (MGF) of end-to-end signal-to-noise ratio of 2-hop multi-relay
system, which is In this paper, we proposed a novel efficient method of analyzing the ergodic channel
capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a
very tight approximate moment applicable to myriad of fading environments including mixed and
composite fading channels. Three distinct adaptive source transmission policies were considered in our
analysis namely: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate
adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). The proposed frame
work based on the novel approximate MGF method is sufficiently general to encapsulate all types of fading
environments (especially for the analysis of the mixed fading case)and provides significant advantage to
model wireless system for mixed and composite fading channel. In addition to simplifying computation
complexity of ergodic capacity for CAF relaying schemes treated in literature, we also derive closed form
expressions for the above three adaptive source transmission policies under Nakagami-m fading with i.n.d
statistics. The accuracy of our proposed method has been validated with existing MGF expressions that are
readily available for specific fading environments in terms of bounds, and via Monte Carlo simulations.
EFFICIENT ANALYSIS OF THE ERGODIC CAPACITY OF COOPERATIVE NON-REGENERATIVE RE...ijwmn
In this paper, we proposed a novel efficient method of analyzing the ergodic channel capacity of the
cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a very tight
approximate moment generating function (MGF) of end-to-end signal-to-noise ratio of 2-hop multi-relay
system, which is In this paper, we proposed a novel efficient method of analyzing the ergodic channel
capacity of the cooperative amplify-and-forward (CAF) relay system. This is accomplished by employing a
very tight approximate moment applicable to myriad of fading environments including mixed and
composite fading channels. Three distinct adaptive source transmission policies were considered in our
analysis namely: (i) constant power with optimal rate adaptation (ORA); (ii) optimal joint power and rate
adaptation (OPRA); and (iii) fixed rate with truncated channel inversion (TCIFR). The proposed frame
work based on the novel approximate MGF method is sufficiently general to encapsulate all types of fading
environments (especially for the analysis of the mixed fading case)and provides significant advantage to
model wireless system for mixed and composite fading channel. In addition to simplifying computation
complexity of ergodic capacity for CAF relaying schemes treated in literature, we also derive closed form
expressions for the above three adaptive source transmission policies under Nakagami-m fading with i.n.d
statistics. The accuracy of our proposed method has been validated with existing MGF expressions that are
readily available for specific fading environments in terms of bounds, and via Monte Carlo simulations.
Beamforming with per antenna power constraint and transmit antenna selection ...sipij
In this paper, transmit beamforming and antenna selection techniques are presented for the Cooperative
Distributed Antenna System. Beamforming technique with minimum total weighted transmit power
satisfying threshold SINR and Per-Antenna Power constraints is formulated as a convex optimization
problem for the efficient performance of Distributed Antenna System (DAS). Antenna Selection technique is
implemented in this paper to select the optimum Remote Antenna Units from all the available ones. This
achieves the best compromise between capacity and system complexity. Dual polarized and Triple
Polarized systems are considered. Simulation results prove that by integrating Beamforming with DAS
enhances its performance. Also by using convex optimization in Antenna Selection enhances the
performance of multi polarized systems.
COMPARISON OF SISO & MIMO TECHNIQUES IN WIRELESS COMMUNICATIONJournal For Research
This paper compares MIMO vs SISO and mention difference between SISO and MIMO techniques. These are techniques based on number of antennas used at the transmitter and the receiver. SISO has been in use since the invention of wireless system.MIMO concept has been recently added to the wireless system. There are different MIMO algorithms which have been developed for two main reasons to increase coverage and to increase the data rates. SISO means Single Input Single Output while MIMO means Multiple Input Multiple Output.
Pilot Decontamination over Time Frequency and Space Domains in Multi-Cell Ma...IJECEIAES
In this article, we show that Pilot contamination problem can be seen as a source separation problem using time, frequency, and space domains. Our method capitalizes on a nonunitary joint diagonalization of spatial quadratic time-frequency (STFD) signal representation to identify the desired and interfering users. We first compute the noise subspace from the STFD matrices selected appropriately. Secondly, we use the noise subspace obtained to estimate the Elevation (El) and the Azimuth (Az) angles for which the MUSIC cost function is maximized. Numerical simulations are provided to illustrate the effectiveness and the behavior of the proposed approach.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Channel Estimation Techniques in MIMO-OFDM LTE SystemsCauses and Effects of C...IJERA Editor
There is an increasing demand for high data transmission rates with the evolution of the very large scale integration (VLSI) technology. The multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) systems are used to fulfill these requirements because of their unique properties such as high spectral efficiency, high data rate and resistance towards multipath propagation. MIMO-OFDM systems are finding their applications in the modern wireless communication systems like IEEE 802.11n, 4G and LTE. They also offer reliable communication with the increased coverage area. The bottleneck to the MIMO-OFDM systems is the estimation of the channel state information (CSI). This can be estimated with the help of any one of the Training Based, Semiblind and Blind Channel estimation algorithms. This paper presents various channel estimation algorithms, optimization techniques and their effective utilization in MIMO-OFDM for modern wireless LTE systems.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
International Journal of Engineering Research and Applications (IJERA) is an open access online peer reviewed international journal that publishes research and review articles in the fields of Computer Science, Neural Networks, Electrical Engineering, Software Engineering, Information Technology, Mechanical Engineering, Chemical Engineering, Plastic Engineering, Food Technology, Textile Engineering, Nano Technology & science, Power Electronics, Electronics & Communication Engineering, Computational mathematics, Image processing, Civil Engineering, Structural Engineering, Environmental Engineering, VLSI Testing & Low Power VLSI Design etc.
Block diagonalization for Multi-user MIMO Beamforming Performance over Rician...
10.1.1.1.4446
1. 1
Fundamental Capacity of MIMO Channels
Andrea Goldsmith, Syed Ali Jafar, Nihar Jindal, and Sriram Vishwanath
Department of Electrical Engineering, Stanford University, Stanford, CA 94305
E-mail : andrea, syed, njindal, sriram@wsl.stanford.edu
November 8, 2002
DRAFT
2. 2
Keywords
MIMO channels, Shannon Capacity, multiuser systems, multicell systems, antenna correlation, channel side
information, beamforming, multiple access channels, broadcast channels.
Abstract
We provide an overview of the extensive recent results on the Shannon capacity of single-user and multiuser
multiple-input multiple-output (MIMO) channels. Although enormous capacity gains have been predicted for such
channels, these predictions are based on somewhat unrealistic assumptions about the underlying time-varying chan-
nel model and how well it can be tracked at the receiver as well as at the transmitter. More realistic assumptions can
dramatically impact the potential capacity gains of MIMO techniques. For time-varying MIMO channels there are
multiple Shannon-theoretic capacity definitions and, for each definition, different correlation models and channel
side information assumptions that we consider. We first provide a comprehensive summary of ergodic and outage
capacity results for single-user MIMO channels. These results indicate that the capacity gain obtained from multi-
ple antennas heavily depends on the amount of channel knowledge at either the receiver or transmitter, the channel
SNR, and the correlation between the channel gains on each antenna element. We then focus attention on the capac-
ity regions for MIMO broadcast and multiple access channels. In contrast to single-user MIMO channels, capacity
results for these multiuser MIMO channels are quite difficult to obtain, even for constant channels. We summarize
capacity results for the MIMO broadcast and multiple access channel for channels that are either constant or fading
with perfect instantaneous knowledge of the antenna gains at both transmitter(s) and receiver(s). We also show
that the MIMO multiple access and broadcast capacity regions are intimately related via a duality transformation.
This transformation is not only useful for proving capacity theorems; it also facilitates finding the optimal transmis-
sion strategy of the nonconvex MIMO broadcast channel using convex optimization techniques applied to the dual
MIMO multiple access channel. Last we discuss capacity results for multicell MIMO channels with base station
cooperation. The base stations then act as a spatially diverse antenna array, and transmission strategies that exploit
this structure exhibit significant capacity gains. This section also provides a brief discussion of system level issues
associated with MIMO cellular. Open problems in this field abound and are discussed throughout the paper.
I. I NTRODUCTION
Wireless systems continue to strive for ever higher data rates. This goal is particularly challenging for
systems that are power, bandwidth, and complexity limited. However, another domain can be exploited
to significantly increase channel capacity: the use of multiple transmit and receive antennas. Pioneering
work by Foschini [22] and Telatar [70] ignited much interest in this area by predicting remarkable spectral
efficiencies for wireless systems with multiple antennas when the channel exhibits rich scattering and
its variations can be accurately tracked. This initial promise of exceptional spectral efficiency almost
“for free” resulted in an explosion of research activity to characterize the theoretical and practical issues
DRAFT
5. 5
tions of partial CSI at the transmitter(s) and or receiver(s). Therefore, the tutorial focus for MIMO mul-
tiuser systems will be on ergodic capacity under perfect CSI at the transmitter and receiver, with a brief
discussion of the known results and open problems for other capacity definitions and CSI assumptions.
Note that the MIMO techniques described herein are applicable to any channel described by a matrix.
Matrix channels describe not only multiantenna systems but also channels with crosstalk [80] and wide-
band channels [72]. While the focus of this tutorial is on memoryless channels (flat-fading), the results
can also be extended to channels with memory (ISI) using well-known methods for incorporating the
channel delay spread into the channel matrix [61], as will be discussed in the next section.
Many practical MIMO techniques have been developed to capitalize on the theoretical capacity gains
predicted by Shannon theory. A major focus of such work is space-time coding: recent work in this
area is summarized in [23]. Other techniques for MIMO systems include space-time modulation [32, 35],
adaptive modulation and coding [11], space-time equalization [3, 52], space-time signal processing [4],
space-time CDMA [15, 36], and space-time OFDM [51, 53, 78]. An overview of the recent advances in
these areas and other practical techniques along with their performance can be found in [27].
The remainder of this paper is organized as follows. In Section II we discuss the capacity of single-
user MIMO systems under different assumptions about channel correlation and channel knowledge at
the transmitter and receiver. This section also describes the optimality of beamforming under partial
transmitter CSI and training issues. Section III describes the capacity regions for both MIMO BCs and
MIMO MACs, along with a duality connection between these regions. The capacity-achieving strategy
of dirty paper coding for the MIMO BC is also discussed. The capacity of multicell systems under dirty-
paper coding and opportunistic beamforming is discussed in Section IV, as well as tradeoffs between
capacity, diversity, and sectorization. Section V summarizes these capacity results and describes some
remaining open problems and design questions associated with MIMO systems.
A table of abbreviations used throughout the paper is given below.
II. S INGLE U SER MIMO
In this section we focus on the capacity of single-user MIMO channels. While most wireless systems
today support multiple users, single-user results are still of much interest for the insight they provide and
their application to channelized systems where users are allocated orthogonal resources (time, frequency
bands, etc.) MIMO channel capacity is also much easier to derive for single users than for multiple
users. Indeed, single-user MIMO capacity results are known for many cases where the corresponding
multiuser problems remain unsolved. In particular, very little is known about multiuser capacity without
DRAFT
9. 9
where
} ~ r ¥ k E €€ †¢5A(fE j¤pn € q (5)
€‡ … ) r ) 8 „ ƒ‚€€
is the capacity with the input covariance matrix E and the expectation is with respect to the
‰iW … ˆ Vˆ
r 4
channel matrix ) . The capacity r¥ k is achieved by transmitting independent complex circular Gaus-
sian symbols along the eigenvectors of r . The powers allocated to each eigenvector are given by the
eigenvalues of r .
It is shown in [70] and [24] that the optimum input covariance matrix that maximizes ergodic capacity
is the scaled identity matrix, i.e. the transmit power is divided equally among all the transmit antennas.
So the ergodic capacity is the expected value of
“
Š †) 8 ‹ f¤pn 4 k
… ) ŒŠ q (6)
Telatar [70] conjectures that the optimal input covariance matrix that maximizes capacity versus outage
is a diagonal matrix with the power equally distributed among a subset of the transmit antennas. In fact,
the higher the outage probability, the smaller the number of transmit antennas used. As the transmit
power is shared equally between more antennas the expectation of
k increases (so the ergodic capacity
increases) but the tails of its distribution decay faster. While this improves capacity versus outage for low
outage probabilities, the capacity versus outage for high outages is decreased. Usually we are interested
in low outage probabilities1 and therefore the usual intuition for outage capacity is that it increases as the
diversity order of the channel increases, i.e. as the capacity CDF becomes steeper. Foschini and Gans [24]
also propose a layered architecture to achieve these capacities with scalar codes. This architecture, called
BLAST (Bell Labs Layered Space Time), shows enormous capacity gains over single antenna systems.
e.g. for 1% outage, at 12 dB SNR and with 12 antennas, the spectral efficiency is shown to be 32
b/s/Hz as opposed to the spectral efficiencies of around 1 b/s/Hz achieved in present day single antenna
systems. While the channel models in [24] and [70] assume uncorrelated and frequency flat fading,
practical channels exhibit both correlated fading as well as frequency selectivity. The need to estimate the
capacity gains of BLAST for practical systems in the presence of channel fade correlations and frequency
selective fading sparked off measurement campaigns reported in [56] [26]. The measured capacities are
found to be about 30% smaller than would be anticipated from an idealized model. However, the capacity
gains over single antenna systems are still overwhelming.
The capacity for high outage probabilities become relevant for schemes that transmit only to the best user. For such schemes,
indeed it is shown in [7] that increasing the number of transmit antennas reduces the average sum capacity.
DRAFT
10. 10
C.3 Capacity with Partial CSIT and Partial CSIR
There has been much interest in the capacity of multiple antenna systems with perfect CSIR but only
partial CSIT. It has been found that unlike single antenna systems where exploiting CSIT does not sig-
nificantly enhance the Shannon capacity [28], for multiple antenna systems the capacity improvement
through even partial CSIT can be substantial. Key work on capacity of such systems by several authors
including Madhow and Visotsky [74], Trott and Narula [59] [58], Jafar and Goldsmith [43] [41] [39], Jor-
sweick and Boche [46] [47] and Simon and Moustakas [57] [68] has provided many interesting results.
In this subsection our aim is to summarize these results.
The optimum input covariance matrix in general can be a full rank matrix which implies vector coding
across the antenna array. Limiting the rank of the input covariance matrix to unity, called beamforming,
essentially leads to a scalar coded system which has a significantly lower complexity for typical array
sizes.
The complexity versus capacity tradeoff in relation to the amount of CSIT is an interesting aspect of
capacity results under partial CSIT. The ability to use scalar codes to achieve capacity with enough CSIT,
also called optimality of beamforming, captures this tradeoff and has been the topic of much research
in itself. Note that vector coding refers to fully unconstrained signaling schemes for the memoryless
MIMO Gaussian channel. Every symbol period, a channel use corresponds to the transmission of a vec-
tor symbol comprised of the inputs to each transmit antenna. Ideally, while decoding vector codewords
the receiver needs to take into account the dependencies in both space and time dimensions and there-
fore the complexity of vector decoding grows exponentially in the number of transmit antennas. A lower
complexity implementation of the vector coding strategy is also possible in the form of several scalar
codewords being transmitted in parallel. It is shown in [39] that without loss of capacity, any input co-
variance matrix, regardless of its rank, can be treated as several scalar codewords encoded independently
at the transmitter and decoded successively at the receiver by subtracting out the contribution from pre-
viously decoded codewords at each stage. However, well known problems associated with successive
decoding and interference subtraction, e.g. error propagation, render this approach unsuitable for use in
practical systems. It is in this context that the question of optimality of beamforming becomes important.
Beamforming transforms the MIMO channel into a single input single output (SISO) channel. Thus, well
established scalar codec technology can be used to approach capacity and since there is only one beam,
interference cancellation is not needed. In the summary given below we include the results on both the
transmitter optimization problem as well as the optimality of beamforming. For simplicity we start with
DRAFT
13. 13
only the deepest level gets all the water when it is sufficiently deeper than the next deepest level and when
the quantity of water is small enough. For mean feedback the optimality of beamforming is found to
depend on transmit power
“ and the quality of feedback defined as the ratio of the norm squared
¦ ¸ º® ¹ ¸¸
¸
of the channel mean vector ) and the channel uncertainty . As the transmit power
p “ is decreased or
the quality of feedback improves beamforming becomes optimal. As mentioned earlier, for perfect CSIT
(Quality of feedback » ¼ˆ ) the optimal input strategy is beamforming, while for zero CSIT (Quality of
feedback i ˆ ) as shown by Telatar [70] the optimal input covariance has full rank, i.e. beamforming is
necessarily sub-optimal. Note that [74], [59], [58] and [41] assume a single receive antenna. Next we
summarize the corresponding results for MIMO capacity with partial CSIT and perfect CSIR.
MIMO Channels
With multiple transmit and receive antennas the covariance feedback case with correlations only at
the transmitter ( 9€ ) is solved by Jafar and Goldsmith in [43]. Like the single receive antenna
‚ 4
case the capacity achieving input covariance matrix is found to have the eigenvectors of the transmit
fade covariance matrix and the eigenvalues are in the same order as the corresponding eigenvalues of
the transmit fade covariance matrix. Jafar and Goldsmith also presented in closed form a mathematical
condition that is both necessary and sufficient for optimality of beamforming in this case. The same
necessary and sufficient condition is also derived independently by Jorsweick and Boche in [46] and
Simon and Moustakas in [68]. In [47] Jorsweick and Boche extend these results to incorporate fade
correlations at the receiver as well. Their results show that while the receive fade correlation matrix does
not affect the eigenvectors of the optimal input covariance matrix, it does affect the eigenvalues. The
general condition for optimality of beamforming found by Jorsweick and Boche depends upon the two
largest eigenvalues of the transmit covariance matrix and all the eigenvalues of the receive covariance
matrix.
The mean feedback case with multiple transmit and receive antennas is solved by Jafar and Goldsmith
in [39] and Moustakas and Simon in [68]. While the general case remains unsolved, solutions are obtained
for the case where the channel mean has rank one [39] and two [68].
These results summarize our discussion of the case with partial CSIT and perfect CSIR. From these
results we notice that the benefits of feeding back CSI from the receiver to the transmitter are two-fold.
Not only does the capacity increase with feedback, but this feedback also allows the transmitter to identify
the stronger channel modes and achieve this higher capacity with simple scalar codewords.
DRAFT
16. 16
„ ¢€ and 9€ . Also, in contrast to the results for the spatially white fading model where adding more
transmit antennas beyond the coherence interval length ( ½ ) does not increase capacity, [38] shows
that additional transmit antennas always increase capacity as long as their channel fading coefficients
are spatially correlated. Thus, in contrast to the results in favor of independent fades with perfect CSIR,
these results indicate that with CCI at the transmitter and the receiver, transmit fade correlations can be
beneficial, making the case for minimizing the spacing between transmit antennas when dealing with
highly mobile, fast fading channels that cannot be accurately measured. It is shown through a simple
example that with coherence time 1 ¡½
4 the capacity with transmit antennas is j¤prw1
¨ q ni db higher
for perfectly correlated fades than for independent fades.
C.6 Frequency Selective Fading Channels
While flat fading is a realistic assumption for narrowband systems where the signal bandwidth is
smaller than the channel coherence bandwidth, broadband communications involve channels that ex-
perience frequency selective fading. Research on the capacity of MIMO systems with frequency selective
fading typically takes the approach of dividing the channel bandwidth into parallel flat fading channels,
and constructing an overall block diagonal channel matrix with the diagonal blocks given by the channel
matrices corresponding to each of these subchannels. Under perfect CSIR and CSIT, the total power
constraint then leads to the usual closed-form waterfilling solution. Note that the waterfill is done si-
multaneously over both space and frequency. Even SISO frequency selective fading channels can be
represented by the MIMO system model (1) in this manner [61]. For MIMO systems, the matrix channel
model is derived by Bolcskei, Gesbert, and Paulraj in [6] based on an analysis of the capacity behavior of
OFDM-based MIMO channels in broadband fading environments. Under the assumption of perfect CSIR
and no CSIT, their results show that in the MIMO case, unlike the SISO case, frequency selective fading
channels may provide advantages over flat fading channels not only in terms of outage capacity but also
in terms of capacity vs outage. In other words, MIMO frequency selective fading channels are shown to
provide both higher diversity gain and higher multiplexing gain than MIMO flat-fading channels. The
measurements in [56] show that frequency selectivity makes the CDF of the capacity steeper and, thus,
increases the capacity for a given outage as compared with the flat-frequency case, but the influence on
the ergodic capacity is small.
DRAFT