b özbek - Academia.edu (original) (raw)

Papers by b özbek

Latin American Applied Research - An international journal, 2018

In the present study, tea leaves (Camellia sinensis) were dried in the domestic microwave oven i... more In the present study, tea leaves (Camellia sinensis) were dried in the domestic microwave oven in order to determine the effect of microwave output power and sample amount on moisture ratio, drying time and effective moisture diffusivity. Five different microwave output power (180-900 W) and five different sample amount (20-100 g) values were used in the drying experiments. The drying data were fitted to some empirical and semi empirical models in order to determine the kinetic parameters. Among of the models proposed, the Page model gave a better fit for all drying conditions applied. The effective moisture diffusivity values were calculated by using the method of slopes at various microwave output powers and sample amounts. Moreover, the activation energy was calculated using an exponential expression based on Arrhenius equation.

Latin American Applied Research - An international journal, 2015

In this study, the goal was to evaluate the ascorbic acid degradation in basil, purslane and cel... more In this study, the goal was to evaluate the ascorbic acid degradation in basil, purslane and celery leaves during microwave drying. The effects of microwave output power and sample amount on ascorbic acid loss in basil, purslane and celery leaves were investigated. The method for the determination of ascorbic acid content was based on the reaction between ascorbic acid and 2,6-dichloroindophenol and was successfully applied to basil, purslane and celery leaves. Increasing microwave output power and decreasing sample amount led to higher degradation rates in basil, purslane and celery leaves. Ascorbic acid degradation kinetics in basil, purslane and celery leaves during microwave drying followed a first-order reaction. The activation energy values were also calculated using an exponential expression based on Arrhenius equation for degradation of ascorbic acid.

Chemical and Biochemical Engineering Quarterly, 2008

The aim of this study was to investigate the influences of substrate concentration, enzyme concen... more The aim of this study was to investigate the influences of substrate concentration, enzyme concentration, temperature and pH on hydrolysis and solubilization of corn gluten as well as enzyme stability. The corn gluten was hydrolyzed by Alcalase enzyme (a bacterial protease produced by a selected strain of Bacillus licheniformis) that was chosen among five commercial enzymes examined. The optimum process conditions for hydrolysis and solubilization were obtained as 30 g L-1 substrate mass concentration, 2.5 mL L-1 enzyme concentration, 55°C and pH 8. Under these conditions, the values of degree of hydrolysis and solubilization were found as 28.4 % and 85.3 % respectively; and enzyme lost its activity by approximatively 74 % at the end of 120 min processing time. Modelling studies were performed to determine the kinetics of hydrolysis, solubilization and enzyme inactivation. The relationship between hydrolysis and solubilization was found linear for all experimental conditions examined. The inactivation energy of Alcalase at the temperature range of 40-55°C was determined to be 67.86 kJ mol-1 .

Chemical and Biochemical Engineering Quarterly

The present investigation describes the effects of the process quantities on enzymatic hydrolysis... more The present investigation describes the effects of the process quantities on enzymatic hydrolysis of milk lactose and enzyme stability. The lactose hydrolysis reactions were carried out in 250 mL of milk by using a commercial β-galactosidase produced from Kluyveromyces marxianus lactis. The residual lactose mass concentration (g L-1) and residual enzyme activity (%) against time were investigated vs. process variables such as temperature, impeller speed and enzyme concentration. Optimum conditions for hydrolysis were obtained as 37 °C, 300 rpm, 1 mL L-1 enzyme concentration and 30 min of processing time. The lactose hydrolysis process resulted in 84 % of hydrolysis degree and 52 % of residual enzyme activity at the optimum experimental conditions obtained. After evaluation of the data, it was found that the kinetics of hydrolysis and enzyme inactivation could be represented by a first order kinetic model and a single-step non-first-order enzyme inactivation kinetic model for all pro...

EURASIP Journal on Wireless Communications and Networking, 2014

The overall performance of cooperative networks is quite sensitive to channel state information (... more The overall performance of cooperative networks is quite sensitive to channel state information (CSI) of serving and interfering base stations (BSs) and affected strongly by quality of limited feedback links. In this paper, we propose two adaptive limited feedback strategies for intercell interference cancelation in multi-antenna multicell networks. The first proposed strategy is developed to improve average multicell capacity assuming a fixed rate feedback link. This algorithm is based on adaptation of the number of bits to quantize CSI of serving and interfering BSs according to transmitter power and location of the user in its own cell. The second proposed strategy is designed in a way to increase average capacity of cell-edge users assuming an adaptive rate feedback link. This algorithm is based on the idea of allocating more bits to quantize CSI of users at cell-edge regions while allocating less bits for users near the serving BS. We illustrate performance of the proposed feedback links for downlink cooperative multi-antenna multicell networks in wireless channels.

EURASIP Journal on Wireless Communications and Networking, 2012

In the next generation of wireless communication, adaptive resource allocation techniques will pl... more In the next generation of wireless communication, adaptive resource allocation techniques will play an important role to improve quality of service and spectral efficiency. In order to employ adaptive fairness scheduling for multiple-input single-output (MISO) orthogonal frequency-division multiple access (OFDMA), the channel state information (CSI) belonging to all users is required at the base station. However, the amount of feedback increases with the number of users, transmit antennas and subchannels. Therefore, it is important to perform a user selection at the receiver side without cooperation among the users and to quantize the CSI. In this article, the reduced feedback channel designs are examined for MISO-OFDMA systems while providing fairness between the users. In order to reduce the feedback rate, we choose the users considering their norm and orthogonality properties as well as their location in the cell. In order to limit the feedback rate, channel direction information is quantized by designing a specific codebook thanks to the proposed criterion. We obtain an expression to determine the amount of required feedback information for MISO-OFDMA systems to support more than one beam per subchannel for a given number of users, subchannels and transmit antennas. The performance results of the reduced feedback channel designs are evaluated for fair scheduling in wireless channels.

Wireless Networks and Mobile Communications, 2010

2010 7th International Symposium on Wireless Communication Systems, 2010

In this paper, we evaluate intercell interference cancelation techniques in cooperative downlink ... more In this paper, we evaluate intercell interference cancelation techniques in cooperative downlink multicell systems. We compare two classical beamforming strategies for the design of the beamforming vectors: maximum ratio combining precoding and partial zero-forcing. Since full channel state information at the transmission is unfeasible, we consider a limited feedback link and compare different strategies for bit partitioning of the feedback information for serving and interferer base stations. We propose a simple adaptive bit partitioning strategy to select an optimum transmission scheme at the base station. We show that the adaptive bit portioning algorithm is improved the sum capacity performance of the multicell networks significantly.

Transactions on Emerging Telecommunications Technologies, 2012

For wireless multiuser multi-input single-output communication systems with adaptive scheduling a... more For wireless multiuser multi-input single-output communication systems with adaptive scheduling and precoding, the users have to feed back their channel state information. However, the amount of feedback data increases with the number of users and the number of transmit antennas. In this paper, we propose a criterion based on the orthogonality between the users' channels to reduce this uplink load. Without cooperation between the users, we only allow users that are semi-orthogonal to feed back their quantized channel information to the base station. We propose a lower bound on the sum rate for the proposed criterion. We show that the performance is almost independent of the number of quantized channel quality information and only channel direction information is important at the transmitter. Then, we consider a noisy feedback channel and propose an algorithm to reduce the noise effect on the analogue feedback.

Mobile relay assisted OFDMA networks that are considered as a good candidate in future deployment... more Mobile relay assisted OFDMA networks that are considered as a good candidate in future deployment scenarios for coverage extension and lower deployment costs are promising solutions for provision of ubiquitous high-data-rate services in wide coverage areas. However, it is required to design efficient resource allocation algorithms to exploit these opportunities. Thus, this paper designs an heuristic resource allocation algorithm based on the queue and channel state information of the users for mobile relay enhanced OFDMA networks. The proposed queue aware algorithm is appropriate for the realistic scenarios and use system resources efficiently. Numerical results revealed that the mobile-relay enhanced scheme improves coverage and assisting users having unfavorable channel conditions such as cell-edge users by increasing the data rate compared to existing fixed-relay enhanced and non-relaying schemes.

After a systematic derivation of space-frequency block codes, the case of two transmitter antenna... more After a systematic derivation of space-frequency block codes, the case of two transmitter antennas where unequal channels are applied to the two symbols that belong to two adjacent subcarriers is considered. At the receiver, the coefficients of the linear combiner are calculated and the expressions are given for the signal-to-noise ratios and different approaches. We propose a scheme that gives the same performance as the ML decoding with computationally efficient structure. The performance of proposed scheme is confirmed by simulations with respect to Hiperlan/2 characteristics. The solution improves the BER performance especially at high compared to ZF approach. The channel coefficients that the scheme needs can be directly estimated by using the

Feedback Strategies for Wireless Communication, 2013

Feedback Strategies for Wireless Communication, 2013

The increasing demand for wireless multimedia has led to coordinated multicell transmission which... more The increasing demand for wireless multimedia has led to coordinated multicell transmission which can increase data rate and reduces outage in cellular systems by mitigating intercell interference (ICI). In order to mitigate ICI, adaptive power allocation and multiple antenna techniques are employed in the multicell networks. In this chapter, we describe limited and reduced feedback strategies for SISO and MISO based cooperative multicell framework in flat fading and frequency selective channels. Since the amount of feedback bits increases with the number of users and base stations, it is important to perform a selection at the user side. In addition to that, the cooperative networks are quite sensitive to the quality of the channel state information of serving and interfering base stations to eliminate inter-cell interference. We examine the limited feedback strategies for multiantenna multicell systems. The purpose is to quantize the CSI belonging to serving and interfering BSs by applying bit partitioning strategies based on different criteria. We illustrate the performance results for cooperative multicell systems with reduced and limited feedback strategies.

Feedback Strategies for Wireless Communication, 2013

In this chapter, we consider different feedback strategies for the case of a single user MIMO wir... more In this chapter, we consider different feedback strategies for the case of a single user MIMO wireless communication system. We examine the case where only one stream is sent from the transmitter to the receiver corresponding to the MISO case or MIMO with receiver combining. Since the information is contained in the channel direction, we mainly consider the case where the normalized MISO channel is quantized, feedback and beamforming is applied at the transmitter. We see that the codebook composed of vectors can also be seen as a finite set of subspaces in the Grassmanian manifold and we derive the codebook criterion, bounds on performance and methods of construction of codebooks. For the MIMO systems where multiple streams are transmitted to the receiver, linear precoding extends the beamforming precoding by premultiplying the different transmitted data streams using a precoding matrix. In that case, the channel direction information is a unitary matrix and depending on the selected criterion the codebook design should be adapted. We study the different techniques to exploit the spatial, time and frequency correlation of the channel. For spatial correlation, we show that the codebook design should be adapted by performing a local packing. For time correlation, the same idea can be exploited. Similarly to correlated source coding, the class of differential feedback strategies are the most promising ones. Finally, in the case of selective MIMO channels, we show that it is possible to reduce the quantity of feedback

Feedback Strategies for Wireless Communication, 2013

In this chapter, we focus on the different feedback strategies for the case of a multiuser wirele... more In this chapter, we focus on the different feedback strategies for the case of a multiuser wireless communication system with multiple transmitter and receiver antennas. Firstly, we analyze the capacity of the multiuser MIMO system with single receive antenna for uplink and downlink by assuming that the full channel state information (CSI) is available at the transmitter. Secondly, we examine the precoding and user selection algorithms for MIMO multiuser systems with one and multiple receive antennas in flat fading and frequency selective wireless channels. Since optimal precoding using dirty paper coding has a prohibitively high computational complexity due to the associated encoding process, it is a great practical interest to design MIMO multiuser systems with low complexity and a minimum CSI requirement at the transmitter side. One suboptimal approach is to apply linear precoding schemes, such as zero forcing beamforming (ZF-BF) or minimum mean square error criterion. Multiuser MIMO wireless communication with ZF-BF requires a brute-force exhaustive search over all possible user sets and the complexity of an exhaustive search is prohibitive when the number of users is large. In order to decrease the complexity of this search, several suboptimal user scheduling algorithms have been designed. Generally, these algorithms fall into two categories: Capacity-based and Frobenius norm-based algorithm. Lastly, we show the effect of reduced and limited feedback information including user selection at the receiver side and quantization for both single carrier and multicarrier transmissions. We perform user selection at the user side since the users having a poor channel (low norm or/and interference) should not take part in the user selection algorithm, nor feedback their channel information. By using a self-discrimination criterion at the receiver side, it is possible to reduce the feedback load and the complexity of the user selection algorithm at base station. We show different user selection criteria and quantization strategies to reduce feedback load for both single and multicarrier communication systems.

Feedback Strategies for Wireless Communication, 2013

In this chapter, we study the different feedback strategies for the case of a single user wireles... more In this chapter, we study the different feedback strategies for the case of a single user wireless communication system where both the transmitter and the receiver are equipped with a single antenna. After a review of the capacity of finite state and Rayleigh fading channel, we have studied the adaptive transmission over time and frequency where rate and power are adapted in order to maximize the spectral efficiency. We have shown that depending on the availability of the channel state information (CSI) at the transmitter (CSIT) and at the receiver (CSIR), the capacity can significantly increase by exploiting the time variation of the channel. We extend the study to consider the important class of frequency selective channel where the power can be optimally shared among the frequencies. We study the adaptive transmission over time and frequency where rate and power are adapted in order to maximize the spectral efficiency. The adaptive modulation and coding where a joint optimization of the coding rate and modulation is a practical scheme to approach capacity. We then study channel prediction at the transmitter to compensate the delay due to feedback link. While average spectral efficiency is not affected by the time delay, there is a significant degradation on the average bit error depending on the length of the prediction filter. For wideband channel, due to correlation of the channel in frequency, the amount of feedback can be reduced by performing data compression. Finally, we consider the Automatic Repeat Request (ARQ) schemes that allow to build a reliable data transmission using ACK/NACK feedback message and data retransmission.

Feedback Strategies for Wireless Communication, 2013

In this chapter, we consider feedback strategies for Long Term Evolution (LTE) and LTE-Advanced b... more In this chapter, we consider feedback strategies for Long Term Evolution (LTE) and LTE-Advanced based wireless communications systems. We first give an overview on LTE standard including frame structure, transmission modes and reference signals for the different releases. We introduce respectively link adaptation considering and channel measurement reporting modes including channel quality information (CQI), precoding matrix index (PMI) and rank indicator (RI). Single user and multiuser MIMO strategies and multicell MIMO transmission schemes including static and dynamic coordination techniques are then reviewed. Finally, design criteria and codebook constructions for downlink and uplink transmission are described in detail.

Feedback Strategies for Wireless Communication, 2013

Background on Wireless Communication 2.1 Introduction In this chapter, we present a brief overvie... more Background on Wireless Communication 2.1 Introduction In this chapter, we present a brief overview of basic wireless communication systems. The chapter starts with a description of wireless communication channel models including multiple input multiple output (MIMO) channel models and dualpolarized antennas channel models. We then discuss about digital modulation and orthogonal frequency division multiplex (OFDM). Finally, we will provide a short introduction on diversity and spatial multiplexing gain in wireless communication systems and MIMO systems. We will introduce different MIMO space-time block codes (STBC) that will be used in the rest of the book. For a detailed treatment of wireless communication systems we refer to the books of Goldsmith [15], Tse and Viswanath [51] or Molisch [32], Proakis [40]. 2.2 Wireless Communication Channel Models 2.2.1 Introduction Compared to wireline channels, the wireless channels vary over time and frequency depending on the objects surrounding the transmitter, the radiated area and the receiver. The variations of the channel strength can be divided into two classes [41]: • Large-scale fading: coming from the path loss due to the distance between the transmitter and the receiver (typically higher than 100 m) and the shadowing due to the obstacles (typically few meters to 100 m). • Small-scale fading: the transmitted signal could arrive at the receiver through multiple paths, which experience different attenuations, arrive at different time delays and phases. It results in constructive or destructive summation of the transmitted signal and causes rapid variations. Furthermore, the path lengths

The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.

Latin American Applied Research - An international journal, 2018

In the present study, tea leaves (Camellia sinensis) were dried in the domestic microwave oven i... more In the present study, tea leaves (Camellia sinensis) were dried in the domestic microwave oven in order to determine the effect of microwave output power and sample amount on moisture ratio, drying time and effective moisture diffusivity. Five different microwave output power (180-900 W) and five different sample amount (20-100 g) values were used in the drying experiments. The drying data were fitted to some empirical and semi empirical models in order to determine the kinetic parameters. Among of the models proposed, the Page model gave a better fit for all drying conditions applied. The effective moisture diffusivity values were calculated by using the method of slopes at various microwave output powers and sample amounts. Moreover, the activation energy was calculated using an exponential expression based on Arrhenius equation.

Latin American Applied Research - An international journal, 2015

In this study, the goal was to evaluate the ascorbic acid degradation in basil, purslane and cel... more In this study, the goal was to evaluate the ascorbic acid degradation in basil, purslane and celery leaves during microwave drying. The effects of microwave output power and sample amount on ascorbic acid loss in basil, purslane and celery leaves were investigated. The method for the determination of ascorbic acid content was based on the reaction between ascorbic acid and 2,6-dichloroindophenol and was successfully applied to basil, purslane and celery leaves. Increasing microwave output power and decreasing sample amount led to higher degradation rates in basil, purslane and celery leaves. Ascorbic acid degradation kinetics in basil, purslane and celery leaves during microwave drying followed a first-order reaction. The activation energy values were also calculated using an exponential expression based on Arrhenius equation for degradation of ascorbic acid.

Chemical and Biochemical Engineering Quarterly, 2008

The aim of this study was to investigate the influences of substrate concentration, enzyme concen... more The aim of this study was to investigate the influences of substrate concentration, enzyme concentration, temperature and pH on hydrolysis and solubilization of corn gluten as well as enzyme stability. The corn gluten was hydrolyzed by Alcalase enzyme (a bacterial protease produced by a selected strain of Bacillus licheniformis) that was chosen among five commercial enzymes examined. The optimum process conditions for hydrolysis and solubilization were obtained as 30 g L-1 substrate mass concentration, 2.5 mL L-1 enzyme concentration, 55°C and pH 8. Under these conditions, the values of degree of hydrolysis and solubilization were found as 28.4 % and 85.3 % respectively; and enzyme lost its activity by approximatively 74 % at the end of 120 min processing time. Modelling studies were performed to determine the kinetics of hydrolysis, solubilization and enzyme inactivation. The relationship between hydrolysis and solubilization was found linear for all experimental conditions examined. The inactivation energy of Alcalase at the temperature range of 40-55°C was determined to be 67.86 kJ mol-1 .

Chemical and Biochemical Engineering Quarterly

The present investigation describes the effects of the process quantities on enzymatic hydrolysis... more The present investigation describes the effects of the process quantities on enzymatic hydrolysis of milk lactose and enzyme stability. The lactose hydrolysis reactions were carried out in 250 mL of milk by using a commercial β-galactosidase produced from Kluyveromyces marxianus lactis. The residual lactose mass concentration (g L-1) and residual enzyme activity (%) against time were investigated vs. process variables such as temperature, impeller speed and enzyme concentration. Optimum conditions for hydrolysis were obtained as 37 °C, 300 rpm, 1 mL L-1 enzyme concentration and 30 min of processing time. The lactose hydrolysis process resulted in 84 % of hydrolysis degree and 52 % of residual enzyme activity at the optimum experimental conditions obtained. After evaluation of the data, it was found that the kinetics of hydrolysis and enzyme inactivation could be represented by a first order kinetic model and a single-step non-first-order enzyme inactivation kinetic model for all pro...

EURASIP Journal on Wireless Communications and Networking, 2014

The overall performance of cooperative networks is quite sensitive to channel state information (... more The overall performance of cooperative networks is quite sensitive to channel state information (CSI) of serving and interfering base stations (BSs) and affected strongly by quality of limited feedback links. In this paper, we propose two adaptive limited feedback strategies for intercell interference cancelation in multi-antenna multicell networks. The first proposed strategy is developed to improve average multicell capacity assuming a fixed rate feedback link. This algorithm is based on adaptation of the number of bits to quantize CSI of serving and interfering BSs according to transmitter power and location of the user in its own cell. The second proposed strategy is designed in a way to increase average capacity of cell-edge users assuming an adaptive rate feedback link. This algorithm is based on the idea of allocating more bits to quantize CSI of users at cell-edge regions while allocating less bits for users near the serving BS. We illustrate performance of the proposed feedback links for downlink cooperative multi-antenna multicell networks in wireless channels.

EURASIP Journal on Wireless Communications and Networking, 2012

In the next generation of wireless communication, adaptive resource allocation techniques will pl... more In the next generation of wireless communication, adaptive resource allocation techniques will play an important role to improve quality of service and spectral efficiency. In order to employ adaptive fairness scheduling for multiple-input single-output (MISO) orthogonal frequency-division multiple access (OFDMA), the channel state information (CSI) belonging to all users is required at the base station. However, the amount of feedback increases with the number of users, transmit antennas and subchannels. Therefore, it is important to perform a user selection at the receiver side without cooperation among the users and to quantize the CSI. In this article, the reduced feedback channel designs are examined for MISO-OFDMA systems while providing fairness between the users. In order to reduce the feedback rate, we choose the users considering their norm and orthogonality properties as well as their location in the cell. In order to limit the feedback rate, channel direction information is quantized by designing a specific codebook thanks to the proposed criterion. We obtain an expression to determine the amount of required feedback information for MISO-OFDMA systems to support more than one beam per subchannel for a given number of users, subchannels and transmit antennas. The performance results of the reduced feedback channel designs are evaluated for fair scheduling in wireless channels.

Wireless Networks and Mobile Communications, 2010

2010 7th International Symposium on Wireless Communication Systems, 2010

In this paper, we evaluate intercell interference cancelation techniques in cooperative downlink ... more In this paper, we evaluate intercell interference cancelation techniques in cooperative downlink multicell systems. We compare two classical beamforming strategies for the design of the beamforming vectors: maximum ratio combining precoding and partial zero-forcing. Since full channel state information at the transmission is unfeasible, we consider a limited feedback link and compare different strategies for bit partitioning of the feedback information for serving and interferer base stations. We propose a simple adaptive bit partitioning strategy to select an optimum transmission scheme at the base station. We show that the adaptive bit portioning algorithm is improved the sum capacity performance of the multicell networks significantly.

Transactions on Emerging Telecommunications Technologies, 2012

For wireless multiuser multi-input single-output communication systems with adaptive scheduling a... more For wireless multiuser multi-input single-output communication systems with adaptive scheduling and precoding, the users have to feed back their channel state information. However, the amount of feedback data increases with the number of users and the number of transmit antennas. In this paper, we propose a criterion based on the orthogonality between the users' channels to reduce this uplink load. Without cooperation between the users, we only allow users that are semi-orthogonal to feed back their quantized channel information to the base station. We propose a lower bound on the sum rate for the proposed criterion. We show that the performance is almost independent of the number of quantized channel quality information and only channel direction information is important at the transmitter. Then, we consider a noisy feedback channel and propose an algorithm to reduce the noise effect on the analogue feedback.

Mobile relay assisted OFDMA networks that are considered as a good candidate in future deployment... more Mobile relay assisted OFDMA networks that are considered as a good candidate in future deployment scenarios for coverage extension and lower deployment costs are promising solutions for provision of ubiquitous high-data-rate services in wide coverage areas. However, it is required to design efficient resource allocation algorithms to exploit these opportunities. Thus, this paper designs an heuristic resource allocation algorithm based on the queue and channel state information of the users for mobile relay enhanced OFDMA networks. The proposed queue aware algorithm is appropriate for the realistic scenarios and use system resources efficiently. Numerical results revealed that the mobile-relay enhanced scheme improves coverage and assisting users having unfavorable channel conditions such as cell-edge users by increasing the data rate compared to existing fixed-relay enhanced and non-relaying schemes.

After a systematic derivation of space-frequency block codes, the case of two transmitter antenna... more After a systematic derivation of space-frequency block codes, the case of two transmitter antennas where unequal channels are applied to the two symbols that belong to two adjacent subcarriers is considered. At the receiver, the coefficients of the linear combiner are calculated and the expressions are given for the signal-to-noise ratios and different approaches. We propose a scheme that gives the same performance as the ML decoding with computationally efficient structure. The performance of proposed scheme is confirmed by simulations with respect to Hiperlan/2 characteristics. The solution improves the BER performance especially at high compared to ZF approach. The channel coefficients that the scheme needs can be directly estimated by using the

Feedback Strategies for Wireless Communication, 2013

Feedback Strategies for Wireless Communication, 2013

The increasing demand for wireless multimedia has led to coordinated multicell transmission which... more The increasing demand for wireless multimedia has led to coordinated multicell transmission which can increase data rate and reduces outage in cellular systems by mitigating intercell interference (ICI). In order to mitigate ICI, adaptive power allocation and multiple antenna techniques are employed in the multicell networks. In this chapter, we describe limited and reduced feedback strategies for SISO and MISO based cooperative multicell framework in flat fading and frequency selective channels. Since the amount of feedback bits increases with the number of users and base stations, it is important to perform a selection at the user side. In addition to that, the cooperative networks are quite sensitive to the quality of the channel state information of serving and interfering base stations to eliminate inter-cell interference. We examine the limited feedback strategies for multiantenna multicell systems. The purpose is to quantize the CSI belonging to serving and interfering BSs by applying bit partitioning strategies based on different criteria. We illustrate the performance results for cooperative multicell systems with reduced and limited feedback strategies.

Feedback Strategies for Wireless Communication, 2013

In this chapter, we consider different feedback strategies for the case of a single user MIMO wir... more In this chapter, we consider different feedback strategies for the case of a single user MIMO wireless communication system. We examine the case where only one stream is sent from the transmitter to the receiver corresponding to the MISO case or MIMO with receiver combining. Since the information is contained in the channel direction, we mainly consider the case where the normalized MISO channel is quantized, feedback and beamforming is applied at the transmitter. We see that the codebook composed of vectors can also be seen as a finite set of subspaces in the Grassmanian manifold and we derive the codebook criterion, bounds on performance and methods of construction of codebooks. For the MIMO systems where multiple streams are transmitted to the receiver, linear precoding extends the beamforming precoding by premultiplying the different transmitted data streams using a precoding matrix. In that case, the channel direction information is a unitary matrix and depending on the selected criterion the codebook design should be adapted. We study the different techniques to exploit the spatial, time and frequency correlation of the channel. For spatial correlation, we show that the codebook design should be adapted by performing a local packing. For time correlation, the same idea can be exploited. Similarly to correlated source coding, the class of differential feedback strategies are the most promising ones. Finally, in the case of selective MIMO channels, we show that it is possible to reduce the quantity of feedback

Feedback Strategies for Wireless Communication, 2013

In this chapter, we focus on the different feedback strategies for the case of a multiuser wirele... more In this chapter, we focus on the different feedback strategies for the case of a multiuser wireless communication system with multiple transmitter and receiver antennas. Firstly, we analyze the capacity of the multiuser MIMO system with single receive antenna for uplink and downlink by assuming that the full channel state information (CSI) is available at the transmitter. Secondly, we examine the precoding and user selection algorithms for MIMO multiuser systems with one and multiple receive antennas in flat fading and frequency selective wireless channels. Since optimal precoding using dirty paper coding has a prohibitively high computational complexity due to the associated encoding process, it is a great practical interest to design MIMO multiuser systems with low complexity and a minimum CSI requirement at the transmitter side. One suboptimal approach is to apply linear precoding schemes, such as zero forcing beamforming (ZF-BF) or minimum mean square error criterion. Multiuser MIMO wireless communication with ZF-BF requires a brute-force exhaustive search over all possible user sets and the complexity of an exhaustive search is prohibitive when the number of users is large. In order to decrease the complexity of this search, several suboptimal user scheduling algorithms have been designed. Generally, these algorithms fall into two categories: Capacity-based and Frobenius norm-based algorithm. Lastly, we show the effect of reduced and limited feedback information including user selection at the receiver side and quantization for both single carrier and multicarrier transmissions. We perform user selection at the user side since the users having a poor channel (low norm or/and interference) should not take part in the user selection algorithm, nor feedback their channel information. By using a self-discrimination criterion at the receiver side, it is possible to reduce the feedback load and the complexity of the user selection algorithm at base station. We show different user selection criteria and quantization strategies to reduce feedback load for both single and multicarrier communication systems.

Feedback Strategies for Wireless Communication, 2013

In this chapter, we study the different feedback strategies for the case of a single user wireles... more In this chapter, we study the different feedback strategies for the case of a single user wireless communication system where both the transmitter and the receiver are equipped with a single antenna. After a review of the capacity of finite state and Rayleigh fading channel, we have studied the adaptive transmission over time and frequency where rate and power are adapted in order to maximize the spectral efficiency. We have shown that depending on the availability of the channel state information (CSI) at the transmitter (CSIT) and at the receiver (CSIR), the capacity can significantly increase by exploiting the time variation of the channel. We extend the study to consider the important class of frequency selective channel where the power can be optimally shared among the frequencies. We study the adaptive transmission over time and frequency where rate and power are adapted in order to maximize the spectral efficiency. The adaptive modulation and coding where a joint optimization of the coding rate and modulation is a practical scheme to approach capacity. We then study channel prediction at the transmitter to compensate the delay due to feedback link. While average spectral efficiency is not affected by the time delay, there is a significant degradation on the average bit error depending on the length of the prediction filter. For wideband channel, due to correlation of the channel in frequency, the amount of feedback can be reduced by performing data compression. Finally, we consider the Automatic Repeat Request (ARQ) schemes that allow to build a reliable data transmission using ACK/NACK feedback message and data retransmission.

Feedback Strategies for Wireless Communication, 2013

In this chapter, we consider feedback strategies for Long Term Evolution (LTE) and LTE-Advanced b... more In this chapter, we consider feedback strategies for Long Term Evolution (LTE) and LTE-Advanced based wireless communications systems. We first give an overview on LTE standard including frame structure, transmission modes and reference signals for the different releases. We introduce respectively link adaptation considering and channel measurement reporting modes including channel quality information (CQI), precoding matrix index (PMI) and rank indicator (RI). Single user and multiuser MIMO strategies and multicell MIMO transmission schemes including static and dynamic coordination techniques are then reviewed. Finally, design criteria and codebook constructions for downlink and uplink transmission are described in detail.

Feedback Strategies for Wireless Communication, 2013

Background on Wireless Communication 2.1 Introduction In this chapter, we present a brief overvie... more Background on Wireless Communication 2.1 Introduction In this chapter, we present a brief overview of basic wireless communication systems. The chapter starts with a description of wireless communication channel models including multiple input multiple output (MIMO) channel models and dualpolarized antennas channel models. We then discuss about digital modulation and orthogonal frequency division multiplex (OFDM). Finally, we will provide a short introduction on diversity and spatial multiplexing gain in wireless communication systems and MIMO systems. We will introduce different MIMO space-time block codes (STBC) that will be used in the rest of the book. For a detailed treatment of wireless communication systems we refer to the books of Goldsmith [15], Tse and Viswanath [51] or Molisch [32], Proakis [40]. 2.2 Wireless Communication Channel Models 2.2.1 Introduction Compared to wireline channels, the wireless channels vary over time and frequency depending on the objects surrounding the transmitter, the radiated area and the receiver. The variations of the channel strength can be divided into two classes [41]: • Large-scale fading: coming from the path loss due to the distance between the transmitter and the receiver (typically higher than 100 m) and the shadowing due to the obstacles (typically few meters to 100 m). • Small-scale fading: the transmitted signal could arrive at the receiver through multiple paths, which experience different attenuations, arrive at different time delays and phases. It results in constructive or destructive summation of the transmitted signal and causes rapid variations. Furthermore, the path lengths

The use of general descriptive names, registered names, trademarks, service marks, etc. in this p... more The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. While the advice and information in this book are believed to be true and accurate at the date of publication, neither the authors nor the editors nor the publisher can accept any legal responsibility for any errors or omissions that may be made. The publisher makes no warranty, express or implied, with respect to the material contained herein.