AbstractThe Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme with its many ad... more AbstractThe Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme with its many advantages, such as robustness to multipath fading, is characterized by the Gaussian-like signal behavior with a relatively high peak-to-average power ratio (PAPR). ...
International Symposium on Performance Evaluation of Computer and Telecommunication Systems, Jul 11, 2010
AbstractAnomalous activities such as flash crowd/event and denial of service (DoS) overload a po... more AbstractAnomalous activities such as flash crowd/event and denial of service (DoS) overload a pool of servers that hosts web contents. This is a great challenge for the 24 by 7 provision of Web contents and may result in interruption of the Web services. Therefore, it is very ...
Turbo Codes&Related Topics; 6th International ITG-Conference on Source and Channel Coding (TURBOCODING), 2006 4th International Symposium on, Apr 3, 2006
ABSTRACT Trellis termination of turbo codes is critical for maintaining their good performance, e... more ABSTRACT Trellis termination of turbo codes is critical for maintaining their good performance, especially for short information blocks when the deterministic interleaver is sought to reduce the complexity of signaling the interleaver permutation. To address this problem, this paper introduces a new type of turbo code called the Return to Zero (RZ) turbo code whose both component encoders are brought to the initial (zero) state. Specifically, a general mathematical model is built in this paper to serve as the theoretical foundation of RZ turbo codes. The model is used to compute the state of a general recursive systematic convolutional (RSC) encoder. Based on this model, a unique duo property of certain class (full feedback) of RSC encoders is demonstrated which is further used to introduce a new type of interleaver called the RZ interleaver. This interleaver is capable of processing the input sequence of bits in such a way that it can bring both encoders into the initial state. Simulation results presented in this paper show that the RZ turbo code can achieve almost the same performance as that of the traditional turbo code when the interleaver size is small or medium.
ABSTRACT We consider the performance of frequency-hopping spread spectrum (FH SS) radio networks ... more ABSTRACT We consider the performance of frequency-hopping spread spectrum (FH SS) radio networks in a Poisson field of interfering terminals using the same modulation and power. The problem is relevant to wireless random-access communication systems where little information about transmitters requires stochastic modeling of their positions. Assuming that the signal strength is attenuated over distance r on average as 1/r m, we show that the interference in the network could be modeled as a mixture of Gaussian and α-stable noise. Based on this modeling, we derive expressions for the probability of error (Pe ) for systems with M-ary frequency shift keying (FSK) which use conventional envelope detectors. Because conventional envelope detectors are optimum only in Gaussian noise and are suboptimum in the noise considered, we also investigate noncoherent detectors which offer improved performance. We examine receivers with limiting nonlinearities and detectors which are optimal in Cauchy noise. Numerical calculations and Monte Carlo simulations are provided to confirm the accuracy of the analysis presented. The results obtained are useful in the performance evaluation of multiple-access radio networks in environments varying from urban settings to office buildings with deterministic and stochastic propagation laws such as lognormal shadowing and Rayleigh fading
This paper proposes a new method for peak-to-average power ratio (PAPR) reduction in orthogonal f... more This paper proposes a new method for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems using forward error correction (FEC). The scheme combines the intentional insertion of correctable errors into the data stream with a specialized bit mapping. The latter deviates from traditional Gray encoding of bits into modulation symbols in order to maximize the benefits of FEC-based PAPR reduction. Using the code redundancy, the proposed scheme achieves significant reduction in PAPR and satisfactory bit error rate (BER) performance at the expense of acceptable computational complexity. Specifically, the complementary cumulative distribution function (CCDF) of the coded signal shows about a 5dB improvement over the original OFDM signal. In addition, BER performance in an additive white Gaussian noise demonstrates trade-offs between reduction in PAPR and remaining error correction capability of the deployed codes.
This paper presents the integration of distributed space-time block coding (STBC) and signal alig... more This paper presents the integration of distributed space-time block coding (STBC) and signal alignment (SA) in multiple-input multiple-output (MIMO) Y channels where multiple terminals communicate with each other in a bi-directional manner via the relay. The objective is to take advantage of the STBC diversity gain without losing much of the high bandwidth efficiency in MIMO Y channel schemes with SA alone. The proposed deployment of STBC represents a form of cooperative coding between the terminals and is referred to as networked MIMO. Specifically, by a thoughtful design of pre-processing vectors and scheduling of transmissions, the signals with mutual information in bi-directional links between terminals are aligned into proper spatial dimensions according to the selected space-time block code. The transmission schemes are also optimized to reduce computational complexity and improve time slot utilization. It is demonstrated with simulations that the proposed design in a three-user MIMO channel offers significant coding gain of 25 dB at the bit error rate (BER) of 10−3 over the conventional MIMO channel signaling in Rayleigh fading channels. This improvement is achieved at the expense of reducing the bandwidth efficiency by a factor of 7/2.
This paper considers multi-way communications among three users equipped with multiple-input mult... more This paper considers multi-way communications among three users equipped with multiple-input multiple-output (MIMO) transceivers that exchange massages between each other via two amplify-and-forward (AF) co-located relays. In this network with half-duplex MIMO relays, the wireless medium is simultaneously utilized for time-slotted transmissions by one of the users and one of the relays in order to increase the network capacity. The relays successively relay the signals creating inter-relay interference (IRI), which limits the bit error rate (BER) performance. To mitigate the IRI, this paper develops a cancellation technique at the receiving side of the users through specialized signal processing and scheduling of transmissions with opportunistic listening. The full IRI cancellation is possible assuming that every transceiver knows its receiving channel state information (CSI) and the inter-relay CSI. When all nodes - users and relays - are equipped with M antennas, the proposed scheme allows to exchange M messages per time slot which doubles the capacity of the network over the conventional AF system operating with a single relay in one-way setup. Simulation results document the effectiveness of the developed scheme in terms of channel capacity and the BER performance.
This paper introduces a novel transmission technique named Beam Angle Channel Modulation (BACM) t... more This paper introduces a novel transmission technique named Beam Angle Channel Modulation (BACM) that uses an antenna array to encode the information symbols into the angle of propagation (and arrival) wave in the wireless channel. At the encoder, the block of information bits is mapped into two symbols: (i) a spatial symbol selecting the direction of arrival of the amplitude and phase modulated carrier signal and (ii) a temporal symbol chosen from the constellation diagram like QAM or PSK. The proposed scheme follows the model for concatenated modulation designs like recently introduced spatial modulation (SM). The use of the transmitted signal angle through antenna array beamforming increases the spectral efficiency of the single-input single-output (SISO) conventional (temporal) modulation by the base-two logarithm of the number of spatial beams that can be resolved (detected) at the receiver. Direction-of-arrival type detection for spatial symbols is developed using a linear array of receive antennas. It is demonstrated that the detection reliability of the spatial symbols in BACM is determined by the number of antennas used at the receiver and the actual angles of signal arrival.
These papers are from the Canadian Conference on Electrical and Computer Engineering, held in 200... more These papers are from the Canadian Conference on Electrical and Computer Engineering, held in 2000. They cover: communications and wireless systems; control theory and applications; robotics; biomedical engineering; power electronics; computer networks; signal processing; avionics; and more.
In this paper, we exploit cooperation between mobile stations and transmissions scheduling in a w... more In this paper, we exploit cooperation between mobile stations and transmissions scheduling in a wireless multicast network to enhance the data rates to multiple single antenna users. The objective is to increase the number of multiplexed signals within a channel use. Specifically, we divide the communication process into two stages. In the first stage, the base station (BS) with multiple antennas using time division multiplexing transmits to different multicast groups in their allocated time slots. The number of messages sent in one time slot is equal to the number of transmit antennas at the BS. In the next stage, the multicast group of "co-located" users and its assigned relays form an independent network, where amplify-and-forward relays aid the recovery of the BS messages, with the users solving a linear system of equations at the end of this stage. All of these subnetworks utilize the available channel concurrently producing an acceptable level of multiple access interference (MAI) where the MAI is controlled using a clustering technique tailored to the location of multicast groups. Simulation results are provided demonstrating the capacity improvements in the proposed scheme.
2016 IEEE 12th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob), 2016
In this paper, we design a signal alignment scheme that exploits orthogonality of spatial signall... more In this paper, we design a signal alignment scheme that exploits orthogonality of spatial signalling dimensions in the multiple-input multiple-output (MIMO) Y channel, where three users send messages to each other through a relay. The antenna configuration in the original MIMO Y channel system imposes limitations on controlling the minimum distance between signaling points representing network coded messages and affects symbol error rate performance. To mitigate this problem, this paper adds one redundant antenna at every user and designs the corresponding precoding vectors to obtain the flexibility in the selection of orthogonal signaling dimensions and to simplify the decoding at the relay. Specifically, as demonstrated through simulations, the design of precoding vectors in the proposed scheme for users improves the bit error rate (BER) performance but the BER is not balanced among the three users. We even the performances via power allocation applied to distribute energy among the users based on their channel conditions. In addition, iterative optimization of the signaling dimensions and time scheduling of transmissions according to channel states are employed to further improve the BER performance.
2016 10th International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP), 2016
This paper develops a time scheduling scheme for generalized K-user multiple-input multiple-outpu... more This paper develops a time scheduling scheme for generalized K-user multiple-input multiple-output (MIMO) Y channels where multiple terminals communicate with each other in a bi-directional manner via the relay. The objective is to decrease the system configuration requirements in terms of antenna numbers at the relay station and user nodes. Specifically, the scheme splits the user nodes into multiple groups and spreads the transmissions over a larger number of time slots (TSs) compared with the original MIMO Y channel scheme. While the latter scheme uses only one medium access control (MAC) and one broadcast (BC) phase, the proposed time scheduling arranges bi-directional data exchanges using specialized precoding in two or more MAC and BC phases between smaller number of users. As a result, the required numbers of antennas at the relay and the user nodes are decreased at the expense of reduced effective throughput. The lower complexity antenna configurations in MIMO Y channels will make the whole system more amenable to practical implementations.
This paper introduces modulation and coding schemes which encode data into beams of antenna array... more This paper introduces modulation and coding schemes which encode data into beams of antenna arrays by exploring the angular models of wireless channels. First, the paper presents Generalized Beam Angle Channel Modulation (Gâ€"BACM) which maps the spatial symbols into multiple angles of wave propagation and arrival. Then, space-time block coding (STBC) strategies for Gâ€"BACM are investigated. In the case of Gâ€"BACM configuration with two simultaneous beams, the block of information bits is mapped into three symbols at the encoder: (i) one, spatial, symbol indexing two beams representing the angles of arrival of the two amplitude and phase modulated (APM) carrier signals and (ii) two APM symbols independently transmitted over two beams. Utilizing simultaneous transmissions on two or more beams improves the bandwidth efficiency and is also used to benefit the diversity aspect of the proposed system. Specifically, STBC strategies for Gâ€"BACM are presented where multiple copies of data streams are transmitted across a number of beams rather than antennas as in conventional multiple-input multiple-output (MIMO) systems. The performance of Gâ€"BACM with and without STBC is analyzed in multipath fading channels when trading-off between the system rate and reliability.
In this paper, we investigate the joint optimization of power allocation and subcarrier assignmen... more In this paper, we investigate the joint optimization of power allocation and subcarrier assignment in the OFDM bidirectional systems where two users exchange data assisted by multiple decode-and-forward (DF) relays. We assume the availability of imperfect channel state information (CSI) that contains a probabilistic uncertainty component and consider its worst effect when performing resource allocation. Moreover, we adopt dynamic network coding to exploit channel diversity. The objective of the resource allocation problem is to maximize the weighted sum rates of the two users subject to quality-of-service (QoS) requirements and individual power constraints. We formulate the problem as a mixed integer programming problem and solve it efficiently in an asymptotic manner by using the dual method. Simulation results show that the proposed scheme is robust to imperfect CSI and provides better performance compared to the scheme with static network coding.
This paper presents an inter-relay interference (IRI) cancellation scheme in amplify-and-forward ... more This paper presents an inter-relay interference (IRI) cancellation scheme in amplify-and-forward (AF) cellular-type networks with successive downlink forwarding. In these half-duplex alternate relaying systems with two hops, the wireless medium in both hops is always utilized through the simultaneous transmissions of the base station (BS) and one of the relays which in turn causes IRI. In this work, the processing to mitigate IRI is performed exclusively at the BS using channel state information (CSI) between the BS and the multiple relays supporting corresponding receivers. The proposed linear precoding exploits the principles of signal alignment at the BS and considers recursive characteristics of IRI. The scheme performance is affected by the noise accumulation which is controlled in this paper by (i) scheduling relays as to benefit from spatial attenuation of signals and (ii) periodically re-initializing BS transmissions where some of the time slots are not utilized for the BS transmissions. Simulation results show the ability of the new scheme to fully cancel IRI as well as demonstrate the performance trade-offs between the bit error rate (BER) improvements and the loss in throughput efficiency due to flushing.
2013 10th IEEE INTERNATIONAL CONFERENCE ON NETWORKING, SENSING AND CONTROL (ICNSC), 2013
ABSTRACT This paper considers energy efficient information dissemination in Wireless Sensor Netwo... more ABSTRACT This paper considers energy efficient information dissemination in Wireless Sensor Networks (WSNs) deploying co-operating nodes which by adjusting their transmission ranges minimize the total transmitted power in the network. Specifically, the design of routing protocols with a single relay node along a data path is proposed for multiple unicast sessions in a network with randomly distributed nodes. The protocols take advantage of topological diversity created by adapting the transmission power and exploit the benefits of network coding in a system where nodes are periodically generating data packets. Energy efficiency of the conventional, store-and-forward, and network coding based relaying schemes is analyzed in different propagation conditions and for various node densities. The best-case improvement in the energy efficiency achievable with network coding over store-and-forward is 25% for two node exchange of data. In WSNs, it is demonstrated through simulations that network coding offers realistically between 11% to 19% energy savings over the store-and-forward strategy. The deployment of the relaying node contributes to the improvement in energy efficiency over direct transmissions in a range of 80%.
AbstractThe Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme with its many ad... more AbstractThe Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme with its many advantages, such as robustness to multipath fading, is characterized by the Gaussian-like signal behavior with a relatively high peak-to-average power ratio (PAPR). ...
International Symposium on Performance Evaluation of Computer and Telecommunication Systems, Jul 11, 2010
AbstractAnomalous activities such as flash crowd/event and denial of service (DoS) overload a po... more AbstractAnomalous activities such as flash crowd/event and denial of service (DoS) overload a pool of servers that hosts web contents. This is a great challenge for the 24 by 7 provision of Web contents and may result in interruption of the Web services. Therefore, it is very ...
Turbo Codes&Related Topics; 6th International ITG-Conference on Source and Channel Coding (TURBOCODING), 2006 4th International Symposium on, Apr 3, 2006
ABSTRACT Trellis termination of turbo codes is critical for maintaining their good performance, e... more ABSTRACT Trellis termination of turbo codes is critical for maintaining their good performance, especially for short information blocks when the deterministic interleaver is sought to reduce the complexity of signaling the interleaver permutation. To address this problem, this paper introduces a new type of turbo code called the Return to Zero (RZ) turbo code whose both component encoders are brought to the initial (zero) state. Specifically, a general mathematical model is built in this paper to serve as the theoretical foundation of RZ turbo codes. The model is used to compute the state of a general recursive systematic convolutional (RSC) encoder. Based on this model, a unique duo property of certain class (full feedback) of RSC encoders is demonstrated which is further used to introduce a new type of interleaver called the RZ interleaver. This interleaver is capable of processing the input sequence of bits in such a way that it can bring both encoders into the initial state. Simulation results presented in this paper show that the RZ turbo code can achieve almost the same performance as that of the traditional turbo code when the interleaver size is small or medium.
ABSTRACT We consider the performance of frequency-hopping spread spectrum (FH SS) radio networks ... more ABSTRACT We consider the performance of frequency-hopping spread spectrum (FH SS) radio networks in a Poisson field of interfering terminals using the same modulation and power. The problem is relevant to wireless random-access communication systems where little information about transmitters requires stochastic modeling of their positions. Assuming that the signal strength is attenuated over distance r on average as 1/r m, we show that the interference in the network could be modeled as a mixture of Gaussian and α-stable noise. Based on this modeling, we derive expressions for the probability of error (Pe ) for systems with M-ary frequency shift keying (FSK) which use conventional envelope detectors. Because conventional envelope detectors are optimum only in Gaussian noise and are suboptimum in the noise considered, we also investigate noncoherent detectors which offer improved performance. We examine receivers with limiting nonlinearities and detectors which are optimal in Cauchy noise. Numerical calculations and Monte Carlo simulations are provided to confirm the accuracy of the analysis presented. The results obtained are useful in the performance evaluation of multiple-access radio networks in environments varying from urban settings to office buildings with deterministic and stochastic propagation laws such as lognormal shadowing and Rayleigh fading
This paper proposes a new method for peak-to-average power ratio (PAPR) reduction in orthogonal f... more This paper proposes a new method for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems using forward error correction (FEC). The scheme combines the intentional insertion of correctable errors into the data stream with a specialized bit mapping. The latter deviates from traditional Gray encoding of bits into modulation symbols in order to maximize the benefits of FEC-based PAPR reduction. Using the code redundancy, the proposed scheme achieves significant reduction in PAPR and satisfactory bit error rate (BER) performance at the expense of acceptable computational complexity. Specifically, the complementary cumulative distribution function (CCDF) of the coded signal shows about a 5dB improvement over the original OFDM signal. In addition, BER performance in an additive white Gaussian noise demonstrates trade-offs between reduction in PAPR and remaining error correction capability of the deployed codes.
This paper presents the integration of distributed space-time block coding (STBC) and signal alig... more This paper presents the integration of distributed space-time block coding (STBC) and signal alignment (SA) in multiple-input multiple-output (MIMO) Y channels where multiple terminals communicate with each other in a bi-directional manner via the relay. The objective is to take advantage of the STBC diversity gain without losing much of the high bandwidth efficiency in MIMO Y channel schemes with SA alone. The proposed deployment of STBC represents a form of cooperative coding between the terminals and is referred to as networked MIMO. Specifically, by a thoughtful design of pre-processing vectors and scheduling of transmissions, the signals with mutual information in bi-directional links between terminals are aligned into proper spatial dimensions according to the selected space-time block code. The transmission schemes are also optimized to reduce computational complexity and improve time slot utilization. It is demonstrated with simulations that the proposed design in a three-user MIMO channel offers significant coding gain of 25 dB at the bit error rate (BER) of 10−3 over the conventional MIMO channel signaling in Rayleigh fading channels. This improvement is achieved at the expense of reducing the bandwidth efficiency by a factor of 7/2.
This paper considers multi-way communications among three users equipped with multiple-input mult... more This paper considers multi-way communications among three users equipped with multiple-input multiple-output (MIMO) transceivers that exchange massages between each other via two amplify-and-forward (AF) co-located relays. In this network with half-duplex MIMO relays, the wireless medium is simultaneously utilized for time-slotted transmissions by one of the users and one of the relays in order to increase the network capacity. The relays successively relay the signals creating inter-relay interference (IRI), which limits the bit error rate (BER) performance. To mitigate the IRI, this paper develops a cancellation technique at the receiving side of the users through specialized signal processing and scheduling of transmissions with opportunistic listening. The full IRI cancellation is possible assuming that every transceiver knows its receiving channel state information (CSI) and the inter-relay CSI. When all nodes - users and relays - are equipped with M antennas, the proposed scheme allows to exchange M messages per time slot which doubles the capacity of the network over the conventional AF system operating with a single relay in one-way setup. Simulation results document the effectiveness of the developed scheme in terms of channel capacity and the BER performance.
This paper introduces a novel transmission technique named Beam Angle Channel Modulation (BACM) t... more This paper introduces a novel transmission technique named Beam Angle Channel Modulation (BACM) that uses an antenna array to encode the information symbols into the angle of propagation (and arrival) wave in the wireless channel. At the encoder, the block of information bits is mapped into two symbols: (i) a spatial symbol selecting the direction of arrival of the amplitude and phase modulated carrier signal and (ii) a temporal symbol chosen from the constellation diagram like QAM or PSK. The proposed scheme follows the model for concatenated modulation designs like recently introduced spatial modulation (SM). The use of the transmitted signal angle through antenna array beamforming increases the spectral efficiency of the single-input single-output (SISO) conventional (temporal) modulation by the base-two logarithm of the number of spatial beams that can be resolved (detected) at the receiver. Direction-of-arrival type detection for spatial symbols is developed using a linear array of receive antennas. It is demonstrated that the detection reliability of the spatial symbols in BACM is determined by the number of antennas used at the receiver and the actual angles of signal arrival.
These papers are from the Canadian Conference on Electrical and Computer Engineering, held in 200... more These papers are from the Canadian Conference on Electrical and Computer Engineering, held in 2000. They cover: communications and wireless systems; control theory and applications; robotics; biomedical engineering; power electronics; computer networks; signal processing; avionics; and more.
In this paper, we exploit cooperation between mobile stations and transmissions scheduling in a w... more In this paper, we exploit cooperation between mobile stations and transmissions scheduling in a wireless multicast network to enhance the data rates to multiple single antenna users. The objective is to increase the number of multiplexed signals within a channel use. Specifically, we divide the communication process into two stages. In the first stage, the base station (BS) with multiple antennas using time division multiplexing transmits to different multicast groups in their allocated time slots. The number of messages sent in one time slot is equal to the number of transmit antennas at the BS. In the next stage, the multicast group of "co-located" users and its assigned relays form an independent network, where amplify-and-forward relays aid the recovery of the BS messages, with the users solving a linear system of equations at the end of this stage. All of these subnetworks utilize the available channel concurrently producing an acceptable level of multiple access interference (MAI) where the MAI is controlled using a clustering technique tailored to the location of multicast groups. Simulation results are provided demonstrating the capacity improvements in the proposed scheme.
2016 IEEE 12th International Conference on Wireless and Mobile Computing, Networking and Communications (WiMob), 2016
In this paper, we design a signal alignment scheme that exploits orthogonality of spatial signall... more In this paper, we design a signal alignment scheme that exploits orthogonality of spatial signalling dimensions in the multiple-input multiple-output (MIMO) Y channel, where three users send messages to each other through a relay. The antenna configuration in the original MIMO Y channel system imposes limitations on controlling the minimum distance between signaling points representing network coded messages and affects symbol error rate performance. To mitigate this problem, this paper adds one redundant antenna at every user and designs the corresponding precoding vectors to obtain the flexibility in the selection of orthogonal signaling dimensions and to simplify the decoding at the relay. Specifically, as demonstrated through simulations, the design of precoding vectors in the proposed scheme for users improves the bit error rate (BER) performance but the BER is not balanced among the three users. We even the performances via power allocation applied to distribute energy among the users based on their channel conditions. In addition, iterative optimization of the signaling dimensions and time scheduling of transmissions according to channel states are employed to further improve the BER performance.
2016 10th International Symposium on Communication Systems, Networks and Digital Signal Processing (CSNDSP), 2016
This paper develops a time scheduling scheme for generalized K-user multiple-input multiple-outpu... more This paper develops a time scheduling scheme for generalized K-user multiple-input multiple-output (MIMO) Y channels where multiple terminals communicate with each other in a bi-directional manner via the relay. The objective is to decrease the system configuration requirements in terms of antenna numbers at the relay station and user nodes. Specifically, the scheme splits the user nodes into multiple groups and spreads the transmissions over a larger number of time slots (TSs) compared with the original MIMO Y channel scheme. While the latter scheme uses only one medium access control (MAC) and one broadcast (BC) phase, the proposed time scheduling arranges bi-directional data exchanges using specialized precoding in two or more MAC and BC phases between smaller number of users. As a result, the required numbers of antennas at the relay and the user nodes are decreased at the expense of reduced effective throughput. The lower complexity antenna configurations in MIMO Y channels will make the whole system more amenable to practical implementations.
This paper introduces modulation and coding schemes which encode data into beams of antenna array... more This paper introduces modulation and coding schemes which encode data into beams of antenna arrays by exploring the angular models of wireless channels. First, the paper presents Generalized Beam Angle Channel Modulation (Gâ€"BACM) which maps the spatial symbols into multiple angles of wave propagation and arrival. Then, space-time block coding (STBC) strategies for Gâ€"BACM are investigated. In the case of Gâ€"BACM configuration with two simultaneous beams, the block of information bits is mapped into three symbols at the encoder: (i) one, spatial, symbol indexing two beams representing the angles of arrival of the two amplitude and phase modulated (APM) carrier signals and (ii) two APM symbols independently transmitted over two beams. Utilizing simultaneous transmissions on two or more beams improves the bandwidth efficiency and is also used to benefit the diversity aspect of the proposed system. Specifically, STBC strategies for Gâ€"BACM are presented where multiple copies of data streams are transmitted across a number of beams rather than antennas as in conventional multiple-input multiple-output (MIMO) systems. The performance of Gâ€"BACM with and without STBC is analyzed in multipath fading channels when trading-off between the system rate and reliability.
In this paper, we investigate the joint optimization of power allocation and subcarrier assignmen... more In this paper, we investigate the joint optimization of power allocation and subcarrier assignment in the OFDM bidirectional systems where two users exchange data assisted by multiple decode-and-forward (DF) relays. We assume the availability of imperfect channel state information (CSI) that contains a probabilistic uncertainty component and consider its worst effect when performing resource allocation. Moreover, we adopt dynamic network coding to exploit channel diversity. The objective of the resource allocation problem is to maximize the weighted sum rates of the two users subject to quality-of-service (QoS) requirements and individual power constraints. We formulate the problem as a mixed integer programming problem and solve it efficiently in an asymptotic manner by using the dual method. Simulation results show that the proposed scheme is robust to imperfect CSI and provides better performance compared to the scheme with static network coding.
This paper presents an inter-relay interference (IRI) cancellation scheme in amplify-and-forward ... more This paper presents an inter-relay interference (IRI) cancellation scheme in amplify-and-forward (AF) cellular-type networks with successive downlink forwarding. In these half-duplex alternate relaying systems with two hops, the wireless medium in both hops is always utilized through the simultaneous transmissions of the base station (BS) and one of the relays which in turn causes IRI. In this work, the processing to mitigate IRI is performed exclusively at the BS using channel state information (CSI) between the BS and the multiple relays supporting corresponding receivers. The proposed linear precoding exploits the principles of signal alignment at the BS and considers recursive characteristics of IRI. The scheme performance is affected by the noise accumulation which is controlled in this paper by (i) scheduling relays as to benefit from spatial attenuation of signals and (ii) periodically re-initializing BS transmissions where some of the time slots are not utilized for the BS transmissions. Simulation results show the ability of the new scheme to fully cancel IRI as well as demonstrate the performance trade-offs between the bit error rate (BER) improvements and the loss in throughput efficiency due to flushing.
2013 10th IEEE INTERNATIONAL CONFERENCE ON NETWORKING, SENSING AND CONTROL (ICNSC), 2013
ABSTRACT This paper considers energy efficient information dissemination in Wireless Sensor Netwo... more ABSTRACT This paper considers energy efficient information dissemination in Wireless Sensor Networks (WSNs) deploying co-operating nodes which by adjusting their transmission ranges minimize the total transmitted power in the network. Specifically, the design of routing protocols with a single relay node along a data path is proposed for multiple unicast sessions in a network with randomly distributed nodes. The protocols take advantage of topological diversity created by adapting the transmission power and exploit the benefits of network coding in a system where nodes are periodically generating data packets. Energy efficiency of the conventional, store-and-forward, and network coding based relaying schemes is analyzed in different propagation conditions and for various node densities. The best-case improvement in the energy efficiency achievable with network coding over store-and-forward is 25% for two node exchange of data. In WSNs, it is demonstrated through simulations that network coding offers realistically between 11% to 19% energy savings over the store-and-forward strategy. The deployment of the relaying node contributes to the improvement in energy efficiency over direct transmissions in a range of 80%.
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Papers by Jacek Ilow