2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 2005
... Morocco. E-mail: {tarik.aitidir, samir.saoudi}@enst-bretagne.fr Abstract-This paper addresses... more ... Morocco. E-mail: {tarik.aitidir, samir.saoudi}@enst-bretagne.fr Abstract-This paper addresses the problem of soft equal-ization and detection of coded MIMO symbols transmitted over a frequency selective fading channel. We ...
Transmission of broadband signals over a multi-antenna multipath fading channel induces intersymb... more Transmission of broadband signals over a multi-antenna multipath fading channel induces intersymbol interference (ISI) at the receiver end. A main task of the space-time signal processor in reception is to combat the ISI effect with the aid of channel equalization techniques. An attractive alternative in case of coded transmission, is turbo equalization which consists on iteratively exchanging decisions between the equalizer and the channel decoder in the form of log-likelihood ratio (LLR) values, to improve information bit decisions at each iteration. This thesis focuses on efficient turbo equalization and multiuser detection schemes for coded space-time transmission over MIMO-ISI channels. We propose a low-complexity turbo receiver architecture for performing channel estimation and equalization iteratively with channel decoding for single user coded space-time transmission, and provide its variant in case of unknown co-channel interference (UCCI)-limited MIMO channels. The soft equalization concept relies on a successive interference cancellation (SIC) scheme derived under a minimum mean square error (MMSE) formalism. It particularly allows low computational complexity compared with existing techniques. The channel estimation algorithm is also MMSE based, and exchanges soft information with the channel decoder and the soft equalizer to improve channel state information (CSI) reliability at each iteration. A second contribution of this thesis is a reduced complexity iterative receiver technique for multiuser multi-antenna coded systems. The considered framework supposes that users employ different pilot sequences. At the receiver end, multiuser interference (MUI) cancellation, channel estimation, equalization, and channel decoding are iterated to reduce each user's error rate at each iteration. Efficient covariance matrices estimation tools are employed for dramatically decreasing receiver's computational complexity. Simulation results show that with a number of receive antennas less than the total number of transmit antennas in the system, the proposed scheme allows good bit error rate (BER) performance compared with the single user bound.
Abstract This paper focuses on the problem of detecting multiuser coded space-time signals transm... more Abstract This paper focuses on the problem of detecting multiuser coded space-time signals transmitted over multi-antenna multipath channel, with imprecise channel knowledge in reception. Computationally efficient methods combining soft multiuser interference (MUI) ...
Abstract—This paper focuses on packet combining for multi-relay systems operating over multiple-i... more Abstract—This paper focuses on packet combining for multi-relay systems operating over multiple-input–multiple-output (MIMO) broadband channel. The work presented in this paper is valid for both amplify-andforward (AF) and decode-and-forward (DF) relaying schemes. First, we drive a communication model in such a way that the destination can see the received signals during the relaying slots as direct retransmissions from the source. We then present a multi-slot communication model where transmission over relaying slots is translated into virtual receive antennas and examine the outage probability of different relaying schemes. Using simulations, we show that this schemes outperform each other depending on the relays location and demonstrate that the multirelay transmissions provide better diversity gain than the conventional hybrid-Automatic repeat request (ARQ). Index Terms—Cooperative relaying, multiple-antenna systems, packet combining, outage probability. I.
Abstract—In this paper, we address the issue of throughputefficient half-duplex constrained relay... more Abstract—In this paper, we address the issue of throughputefficient half-duplex constrained relaying schemes for broadband uplink transmissions over multiple-input multiple-output (MIMO) channels. We introduce a low complexity signal-level cooperative spatial multiplexing (CM) architecture that allows for the shortening of the relaying phase without resorting to any symbol detection or re-mapping at the relay side. Half-duplex latency is thereby reduced, resulting in a remarkable throughput gain compared to amplify-and-forward (AF) relaying scheme. Surprisingly, we show that CM strategy becomes more powerful in boosting uplink throughput as the relay approaches cell edge. I.
Abstract—This paper focuses on turbo packet combining for hybrid AF/DF multi-relay systems operat... more Abstract—This paper focuses on turbo packet combining for hybrid AF/DF multi-relay systems operating over multipleinput–multiple-output (MIMO) broadband channels. We consider virtual antenna based combining strategy that has been widely studied for the point-to-point hybrid ARQ. However, the extension of this combining strategy to hybrid AF/DF cooperative communications is not straightforward. In this paper, we revisit this combining strategy. First, we build an appropriate system model to mask the cooperation. Then, we extend the turbo packet combiner inspired by virtual antenna concept to cooperative communications. Finally, block error rate (BLER) are investigated to demonstrate the gain offered by the studied turbo packet combiner. Index Terms—Cooperative relaying, multiple-antenna systems, turbo equalization, packet combining. I.
In this paper, we consider high-speed wireless packet access using code division multiple access ... more In this paper, we consider high-speed wireless packet access using code division multiple access (CDMA) and multiple-input–multiple-output (MIMO). Current wireless standards, such as high speed packet access (HSPA), have adopted multi-code transmission and hybrid–automatic repeat request (ARQ) as major technologies for delivering high data rates. The key technique in hybrid–ARQ, is that erroneous data packets are kept in the receiver to detect/decode retransmitted ones. This strategy is refereed to as packet combining. In CDMA MIMO-based wireless packet access, multi-code transmission suffers from severe performance degradation due to the loss of code orthogonality caused by both interchip interference (ICI) and co-antenna interference (CAI). This limitation results in large transmission delays when an ARQ mechanism is used in the link layer. In this paper, we investigate efficient minimum mean square error (MMSE) frequency domain equalization (FDE)-based iterative (turbo) packet co...
This paper addresses the issue of efficient turbo packet combining techniques for coded transmiss... more This paper addresses the issue of efficient turbo packet combining techniques for coded transmission with a Chase-type automatic repeat request (ARQ) protocol operating over a multiple-input–multiple-output (MIMO) channel with intersymbol interference (ISI). First of all, we investigate the outage probability and the outagebased power loss of the MIMO-ISI ARQ channel when optimal maximum a posteriori (MAP) turbo packet combining is used at the receiver. We show that the ARQ delay (i.e., the maximum number of ARQ rounds) does not completely translate into a diversity gain. We then introduce two efficient turbo packet combining algorithms that are inspired by minimum mean square error (MMSE)-based turbo equalization techniques. Both schemes can be viewed as low-complexity versions of the optimal MAP turbo combiner. The first scheme is called signal-level turbo combining and performs packet combining and multiple transmission ISI cancellation jointly at the signal-level. The second sch...
Hybrid automatic repeat request (HARQ) is used in high-speed uplink packet access (HSUPA) to incr... more Hybrid automatic repeat request (HARQ) is used in high-speed uplink packet access (HSUPA) to increase the data rate. Chase combining is the simplest of HARQ algorithms. It provides a time diversity and requires a small memory. In this paper, we propose a technique to increase the chase combining efficiency. In this method, HARQ transmissions are seen as additional receive antennas which are jointly combined at chip-level using a space-time linear minimum square error (LMMSE). We demonstrate that the chase combining diversity gain is considerably increased especially for high-order modulation.
This paper addresses the problem of unsupervised soft bit error rate (BER) estimation for any com... more This paper addresses the problem of unsupervised soft bit error rate (BER) estimation for any communications system, where no prior knowledge either about transmitted information bits, or the transceiver scheme is available. We show that the problem of BER estimation is equivalent to estimating the conditional probability density functions (pdf)s of soft channel/receiver outputs. Assuming that the receiver has no analytical model of soft observations, we propose a non parametric Kernel-based pdf estimation technique, and show that the resulting BER estimator is asymptotically unbiased and point-wise consistent. We then introduce an iterative Stochastic Expectation Maximization (EM) algorithm for the estimation of both a priori and a posteriori probabilities of transmitted information bits, and the classification of soft observations according to transmitted bit values. These inputs serve in the iterative Kernel-based estimation procedure of conditional pdfs. We analyze the performan...
This paper focuses on turbo packet combining for multirelay systems operating over multiple-input... more This paper focuses on turbo packet combining for multirelay systems operating over multiple-input-multiple-output (MIMO) broadband channels. We consider a relaying protocol that represents a generalization of the classical point-to-point hy- brid automatic repeat request (ARQ). In this protocol, relays play the role of packet retransmitters instead of the source. Packet com- bining has been widely studied for the point-to-point hybrid ARQ, and it has been shown that the virtual-antenna-concept-based combining strategy exhibits block error rate (BLER) performance that is very close to the matched filter bound. However, the ex- tension of this combining strategy to cooperative communications operating under the framework of broadband MIMO channels is not straightforward. In this paper, we revisit this combining strategy. First, we build an appropriate system model in such a way that the cooperation is disguised and the multirelay system becomes equivalent to a point-to-point hybrid AR...
This paper introduces a new packet combining technique with integrated minimum mean square error ... more This paper introduces a new packet combining technique with integrated minimum mean square error (MMSE) turbo equalization for single carrier broadband multi-antenna coded transmission. The proposed scheme considers each trans- mission as an additional set of virtual receive antennas and combines multiple transmissions in the frequency domain with very low computational complexity. Block error rate (BLER) curves, obtained via computer simulations, indicate that the technique has near optimal performance.
This paper focuses on turbo packet combining for hybrid AF/DF multi-relay systems operating over ... more This paper focuses on turbo packet combining for hybrid AF/DF multi-relay systems operating over multiple-input–multiple-output (MIMO) broadband channels. We con-sider virtual antenna based combining strategy that has been widely studied for the point-to-point hybrid ARQ. However, the extension of this combining strategy to hybrid AF/DF cooperative communications is not straightforward. In this paper, we revisit this combining strategy. First, we build an appropriate system model to mask the cooperation. Then, we extend the turbo packet combiner inspired by virtual antenna concept to cooperative communications. Finally, block error rate (BLER) are investigated to demonstrate the gain offered by the studied turbo packet combiner.
2007 2nd International Symposium on Wireless Pervasive Computing, 2007
Abstract This paper focuses on the problem of turbo equalization for MIMO frequency selective fad... more Abstract This paper focuses on the problem of turbo equalization for MIMO frequency selective fading channels under the presence of unknown co-channel interference (UCCI). We develop an approach where paths' gains computation, UCCI plus noise covariance ...
2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, 2005
... Morocco. E-mail: {tarik.aitidir, samir.saoudi}@enst-bretagne.fr Abstract-This paper addresses... more ... Morocco. E-mail: {tarik.aitidir, samir.saoudi}@enst-bretagne.fr Abstract-This paper addresses the problem of soft equal-ization and detection of coded MIMO symbols transmitted over a frequency selective fading channel. We ...
Transmission of broadband signals over a multi-antenna multipath fading channel induces intersymb... more Transmission of broadband signals over a multi-antenna multipath fading channel induces intersymbol interference (ISI) at the receiver end. A main task of the space-time signal processor in reception is to combat the ISI effect with the aid of channel equalization techniques. An attractive alternative in case of coded transmission, is turbo equalization which consists on iteratively exchanging decisions between the equalizer and the channel decoder in the form of log-likelihood ratio (LLR) values, to improve information bit decisions at each iteration. This thesis focuses on efficient turbo equalization and multiuser detection schemes for coded space-time transmission over MIMO-ISI channels. We propose a low-complexity turbo receiver architecture for performing channel estimation and equalization iteratively with channel decoding for single user coded space-time transmission, and provide its variant in case of unknown co-channel interference (UCCI)-limited MIMO channels. The soft equalization concept relies on a successive interference cancellation (SIC) scheme derived under a minimum mean square error (MMSE) formalism. It particularly allows low computational complexity compared with existing techniques. The channel estimation algorithm is also MMSE based, and exchanges soft information with the channel decoder and the soft equalizer to improve channel state information (CSI) reliability at each iteration. A second contribution of this thesis is a reduced complexity iterative receiver technique for multiuser multi-antenna coded systems. The considered framework supposes that users employ different pilot sequences. At the receiver end, multiuser interference (MUI) cancellation, channel estimation, equalization, and channel decoding are iterated to reduce each user's error rate at each iteration. Efficient covariance matrices estimation tools are employed for dramatically decreasing receiver's computational complexity. Simulation results show that with a number of receive antennas less than the total number of transmit antennas in the system, the proposed scheme allows good bit error rate (BER) performance compared with the single user bound.
Abstract This paper focuses on the problem of detecting multiuser coded space-time signals transm... more Abstract This paper focuses on the problem of detecting multiuser coded space-time signals transmitted over multi-antenna multipath channel, with imprecise channel knowledge in reception. Computationally efficient methods combining soft multiuser interference (MUI) ...
Abstract—This paper focuses on packet combining for multi-relay systems operating over multiple-i... more Abstract—This paper focuses on packet combining for multi-relay systems operating over multiple-input–multiple-output (MIMO) broadband channel. The work presented in this paper is valid for both amplify-andforward (AF) and decode-and-forward (DF) relaying schemes. First, we drive a communication model in such a way that the destination can see the received signals during the relaying slots as direct retransmissions from the source. We then present a multi-slot communication model where transmission over relaying slots is translated into virtual receive antennas and examine the outage probability of different relaying schemes. Using simulations, we show that this schemes outperform each other depending on the relays location and demonstrate that the multirelay transmissions provide better diversity gain than the conventional hybrid-Automatic repeat request (ARQ). Index Terms—Cooperative relaying, multiple-antenna systems, packet combining, outage probability. I.
Abstract—In this paper, we address the issue of throughputefficient half-duplex constrained relay... more Abstract—In this paper, we address the issue of throughputefficient half-duplex constrained relaying schemes for broadband uplink transmissions over multiple-input multiple-output (MIMO) channels. We introduce a low complexity signal-level cooperative spatial multiplexing (CM) architecture that allows for the shortening of the relaying phase without resorting to any symbol detection or re-mapping at the relay side. Half-duplex latency is thereby reduced, resulting in a remarkable throughput gain compared to amplify-and-forward (AF) relaying scheme. Surprisingly, we show that CM strategy becomes more powerful in boosting uplink throughput as the relay approaches cell edge. I.
Abstract—This paper focuses on turbo packet combining for hybrid AF/DF multi-relay systems operat... more Abstract—This paper focuses on turbo packet combining for hybrid AF/DF multi-relay systems operating over multipleinput–multiple-output (MIMO) broadband channels. We consider virtual antenna based combining strategy that has been widely studied for the point-to-point hybrid ARQ. However, the extension of this combining strategy to hybrid AF/DF cooperative communications is not straightforward. In this paper, we revisit this combining strategy. First, we build an appropriate system model to mask the cooperation. Then, we extend the turbo packet combiner inspired by virtual antenna concept to cooperative communications. Finally, block error rate (BLER) are investigated to demonstrate the gain offered by the studied turbo packet combiner. Index Terms—Cooperative relaying, multiple-antenna systems, turbo equalization, packet combining. I.
In this paper, we consider high-speed wireless packet access using code division multiple access ... more In this paper, we consider high-speed wireless packet access using code division multiple access (CDMA) and multiple-input–multiple-output (MIMO). Current wireless standards, such as high speed packet access (HSPA), have adopted multi-code transmission and hybrid–automatic repeat request (ARQ) as major technologies for delivering high data rates. The key technique in hybrid–ARQ, is that erroneous data packets are kept in the receiver to detect/decode retransmitted ones. This strategy is refereed to as packet combining. In CDMA MIMO-based wireless packet access, multi-code transmission suffers from severe performance degradation due to the loss of code orthogonality caused by both interchip interference (ICI) and co-antenna interference (CAI). This limitation results in large transmission delays when an ARQ mechanism is used in the link layer. In this paper, we investigate efficient minimum mean square error (MMSE) frequency domain equalization (FDE)-based iterative (turbo) packet co...
This paper addresses the issue of efficient turbo packet combining techniques for coded transmiss... more This paper addresses the issue of efficient turbo packet combining techniques for coded transmission with a Chase-type automatic repeat request (ARQ) protocol operating over a multiple-input–multiple-output (MIMO) channel with intersymbol interference (ISI). First of all, we investigate the outage probability and the outagebased power loss of the MIMO-ISI ARQ channel when optimal maximum a posteriori (MAP) turbo packet combining is used at the receiver. We show that the ARQ delay (i.e., the maximum number of ARQ rounds) does not completely translate into a diversity gain. We then introduce two efficient turbo packet combining algorithms that are inspired by minimum mean square error (MMSE)-based turbo equalization techniques. Both schemes can be viewed as low-complexity versions of the optimal MAP turbo combiner. The first scheme is called signal-level turbo combining and performs packet combining and multiple transmission ISI cancellation jointly at the signal-level. The second sch...
Hybrid automatic repeat request (HARQ) is used in high-speed uplink packet access (HSUPA) to incr... more Hybrid automatic repeat request (HARQ) is used in high-speed uplink packet access (HSUPA) to increase the data rate. Chase combining is the simplest of HARQ algorithms. It provides a time diversity and requires a small memory. In this paper, we propose a technique to increase the chase combining efficiency. In this method, HARQ transmissions are seen as additional receive antennas which are jointly combined at chip-level using a space-time linear minimum square error (LMMSE). We demonstrate that the chase combining diversity gain is considerably increased especially for high-order modulation.
This paper addresses the problem of unsupervised soft bit error rate (BER) estimation for any com... more This paper addresses the problem of unsupervised soft bit error rate (BER) estimation for any communications system, where no prior knowledge either about transmitted information bits, or the transceiver scheme is available. We show that the problem of BER estimation is equivalent to estimating the conditional probability density functions (pdf)s of soft channel/receiver outputs. Assuming that the receiver has no analytical model of soft observations, we propose a non parametric Kernel-based pdf estimation technique, and show that the resulting BER estimator is asymptotically unbiased and point-wise consistent. We then introduce an iterative Stochastic Expectation Maximization (EM) algorithm for the estimation of both a priori and a posteriori probabilities of transmitted information bits, and the classification of soft observations according to transmitted bit values. These inputs serve in the iterative Kernel-based estimation procedure of conditional pdfs. We analyze the performan...
This paper focuses on turbo packet combining for multirelay systems operating over multiple-input... more This paper focuses on turbo packet combining for multirelay systems operating over multiple-input-multiple-output (MIMO) broadband channels. We consider a relaying protocol that represents a generalization of the classical point-to-point hy- brid automatic repeat request (ARQ). In this protocol, relays play the role of packet retransmitters instead of the source. Packet com- bining has been widely studied for the point-to-point hybrid ARQ, and it has been shown that the virtual-antenna-concept-based combining strategy exhibits block error rate (BLER) performance that is very close to the matched filter bound. However, the ex- tension of this combining strategy to cooperative communications operating under the framework of broadband MIMO channels is not straightforward. In this paper, we revisit this combining strategy. First, we build an appropriate system model in such a way that the cooperation is disguised and the multirelay system becomes equivalent to a point-to-point hybrid AR...
This paper introduces a new packet combining technique with integrated minimum mean square error ... more This paper introduces a new packet combining technique with integrated minimum mean square error (MMSE) turbo equalization for single carrier broadband multi-antenna coded transmission. The proposed scheme considers each trans- mission as an additional set of virtual receive antennas and combines multiple transmissions in the frequency domain with very low computational complexity. Block error rate (BLER) curves, obtained via computer simulations, indicate that the technique has near optimal performance.
This paper focuses on turbo packet combining for hybrid AF/DF multi-relay systems operating over ... more This paper focuses on turbo packet combining for hybrid AF/DF multi-relay systems operating over multiple-input–multiple-output (MIMO) broadband channels. We con-sider virtual antenna based combining strategy that has been widely studied for the point-to-point hybrid ARQ. However, the extension of this combining strategy to hybrid AF/DF cooperative communications is not straightforward. In this paper, we revisit this combining strategy. First, we build an appropriate system model to mask the cooperation. Then, we extend the turbo packet combiner inspired by virtual antenna concept to cooperative communications. Finally, block error rate (BLER) are investigated to demonstrate the gain offered by the studied turbo packet combiner.
2007 2nd International Symposium on Wireless Pervasive Computing, 2007
Abstract This paper focuses on the problem of turbo equalization for MIMO frequency selective fad... more Abstract This paper focuses on the problem of turbo equalization for MIMO frequency selective fading channels under the presence of unknown co-channel interference (UCCI). We develop an approach where paths' gains computation, UCCI plus noise covariance ...
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