2021 3rd IEEE Middle East and North Africa COMMunications Conference (MENACOMM), 2021
Thanks to the recent development of antenna design, localization based on the Direction of Arriva... more Thanks to the recent development of antenna design, localization based on the Direction of Arrival (DoA) of the incident signals is becoming more and more promising approach. This paper presents a direction-based positioning algorithm which can be implemented at the mobile device in 3D schemes. As the mobile orientation is unclear and inconstant, an algorithm utilizing the Direction Difference of Arrival (DDoA) among the incident signals is considered. Because of the complexity in computation, we use the Time of Arrival (ToA) as the additional data for position estimation. As a result, the joint DDoA-ToA method is studied. Moreover, an iterative Maximum Likelihood (ML) estimator for position estimation is presented to rectify the final estimates. Simulation results show significant performance improvement compared to other methods.
Employing dynamic Time Division Duplexing (DynTDD) can increase the system-wide spectral efficien... more Employing dynamic Time Division Duplexing (DynTDD) can increase the system-wide spectral efficiency of scenarios with varying and unbalanced uplink (UL) and downlink (DL) data traffic requirements. However when using DynTDD, a different DL/UL slot configuration is likely to be selected by neighboring cells, leading to Cross Link Interference (CLI) between the Base Stations (BS), which is known as BS-to-BS or DLto-UL interference, and between User Equipments (UE) which is known as UE-to-UE or UL-to-DL interference. Rank deficient channels are frequently encountered in Multi-Input Multi-Output (MIMO) networks, due to poor scattering and keyhole effects, or when using Massive MIMO and moving to mmWave. While the implications of rank deficient channels are well understood for the single user point to point setting, less is known for interference networks. In this paper we study the Degrees of Freedom (DoF) focusing on the UE-to-UE interference, by establishing necessary conditions, for ...
The communication between a multiple-antenna transmitter and multiple receivers (users) with eith... more The communication between a multiple-antenna transmitter and multiple receivers (users) with either a single or multiple-antenna each can be significantly enhanced by providing the channel state information at the transmitter (CSIT) of the users, as this allows for scheduling, beamforming and multiuser multiplexing gains. The traditional view on how to enable CSIT has been as follows so far: In time-division duplexed (TDD) systems, uplink (UL) and downlink (DL) channel reciprocity allows the use of a training sequence in the UL direction, which is exploited to obtain an UL channel estimate. This estimate is in turn recycled in the next downlink slot. In frequency-division duplexed (FDD) systems, which lack the UL and DL reciprocity, the CSIT is provided via the use of a dedicated feedback link of limited capacity between the receivers and the transmitter. In this paper, we focus on TDD systems and put this classical approach in question. In particular, we show that the traditional T...
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific ... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. 1 2
2010 IEEE Global Telecommunications Conference GLOBECOM 2010, 2010
This paper considers a large multiuser time-division duplex (TDD) system, where the base station ... more This paper considers a large multiuser time-division duplex (TDD) system, where the base station (BS) acquires channel state information via pilot signaling from the users. In the downlink the BS employs zero-forcing (ZF) and regularized zero-forcing (RZF) precoding. We derive the optimal sum rate maximizing amount of channel training using sum rate approximations from the large system analysis of MISO downlink channels under (R)ZF precoding. Moreover, in the regime of high signal-to-noise ratio (SNR), we derive approximate solutions of the optimal amount of training for both schemes that are of closed-form. By comparing the two schemes, we find that RZF requires less training than ZF, but the training interval of both schemes is equal for asymptotically high SNR. Furthermore, simulations are carried out which demonstrate the accuracy of our approximate solutions.
2007 IEEE Wireless Communications and Networking Conference, 2007
The problem of joint linear beamforming and scheduling in a MIMO broadcast channel is considered.... more The problem of joint linear beamforming and scheduling in a MIMO broadcast channel is considered. We show how Orthogonal Linear Beamforming (OLBF) can be efficiently combined with a low-complexity user selection algorithm to achieve a large portion of the multiuser capacity. The use of orthogonal transmission enables the transmitter to calculate exact signal-to-interference plus noise ratio (SINR) values during the user selection process. The knowledge of multiuser interference proves to be of particular importance for user scheduling as both the number of users in the cell and the average signal-tonoise ratio (SNR) decrease. The sum capacity of our scheme is characterized in the low-SNR regime, providing analytical results on the performance gain over Zero-Forcing Beamforming (ZFBF). Numerical results show gains over both suboptimal and optimal ZFBF techniques in different scenarios.
GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference, 2009
The communication between a multiple-antenna transmitter and multiple receivers (users) with eith... more The communication between a multiple-antenna transmitter and multiple receivers (users) with either a single or multiple-antenna each can be significantly enhanced by providing the channel state information at the transmitter (CSIT) of the users, as this allows for scheduling, beamforming and multiuser multiplexing gains. The traditional view on how to enable CSIT has been as follows so far: In time-division duplexed (TDD) systems, uplink (UL) and downlink (DL) channel reciprocity allows for the use of a training sequence in any given uplink slot, which is exploited to obtain an uplink channel estimate. This estimate is in turn recycled in the next downlink slot. In frequency-division duplexed (FDD) systems, which lack the UL and DL reciprocity, the CSIT is provided via the use of a dedicated feedback link of limited capacity between the receivers and the transmitter. In this paper, we focus on TDD systems and show that the traditional TDD CSIT acquisition fails to fully exploit the channel reciprocity in its true sense. In fact, we show that the system can benefit from a combined CSIT acquisition strategy mixing the use of limited feedback and that of a training sequence. We demonstrate the potential of our approach in terms of improved CSIT quality under a global training and feedback resource constraint.
2012 International Symposium on Wireless Communication Systems (ISWCS), 2012
We present in this paper a software implementation of a cognitive radio (CR) communication based ... more We present in this paper a software implementation of a cognitive radio (CR) communication based on long term evolution-time division duplex (LTE-TDD) channel reciprocity. We study the problem of calibration and beamforming design for a CR system in which a multiple-input single-output (MISO) secondary link, wants to opportunistically communicate without harming the primary SISO system. Specifically, we evaluate the CR communication through the EURECOM's experimental OpenAirInterface (OAI) software platform. We will show that it is feasible to restore the reciprocity after calibration in a non reciprocal channel, and provide an overview of challenges in the channel estimation for real conditions.
We propose an iterative algorithm to design optimal linear transmitters and receivers in a K-user... more We propose an iterative algorithm to design optimal linear transmitters and receivers in a K-user frequency-flat MIMO Interference Channel (MIMO IFC) with full channel state information (CSI). The transmitters and receivers are optimized to maximize the Weighted Sum Rate (WSR) of the MIMO IFC. Maximization of WSR is desirable since it allows the system to cover all the rate tuples on the Pareto-optimal rate region boundary for a given MIMO IFC. The proposed algorithm is rooted in a recent result [1] showing a correspondence between local optima of the Minimum Weighted Sum Mean Squared Error (MWSMSE) and Maximum Weighted Sum Rate (MWSR) objective functions for the MIMO Broadcast Channel (BC). This connection between the MWSR and MWSMSE is shown to hold true also in the MIMO IFC and is exploited to design an alternating minimization algorithm for MIMO IFC that maximizes the WSR. The MWSMSE-MWSR connection also allows to solve the transmit filter design subproblem in the alternating algorithm by invoking a heuristic solution first proposed in [2],[3]. Another contribution of this paper is to propose an extension of [4] to MIMO problems, following the philosophy of [1] in part. This path is shown to lead in fact to the same iterative algorithm, showing the optimality of the heuristic of [2],[3] when applied in the context of the alternating transmitter-receiver optimization approach of [1].
The communication between a multiple-antenna transmitter and multiple receivers (users) with eith... more The communication between a multiple-antenna transmitter and multiple receivers (users) with either a single or multiple-antenna each can be significantly enhanced by providing the channel state information at the transmitter (CSIT) of the users, as this allows for scheduling, beamforming and multiuser multiplexing gains. The traditional view on how to enable CSIT has been as follows so far: In time-division duplexed (TDD) systems, uplink (UL) and downlink (DL) channel reciprocity allows the use of a training sequence in the UL direction, which is exploited to obtain an UL channel estimate. This estimate is in turn recycled in the next downlink slot. In frequency-division duplexed (FDD) systems, which lack the UL and DL reciprocity, the CSIT is provided via the use of a dedicated feedback link of limited capacity between the receivers and the transmitter. In this paper, we focus on TDD systems and put this classical approach in question. In particular, we show that the traditional TDD setup above fails to fully exploit the channel reciprocity in its true sense. In fact, we show that the system can benefit from a combined CSIT acquisition strategy mixing the use of limited feedback and that of a training sequence. This combining gives rise to a very interesting joint estimation and detection problem for which we propose two iterative algorithms. An outage rate based framework is also developed which gives the optimal resource split between training and feedback. We demonstrate the potential of this hybrid combining in terms of the improved CSIT quality under a global training and feedback resource constraint.
By minimizing a deterministic criterion of the constant modulus (CM) type or of the decisiondirec... more By minimizing a deterministic criterion of the constant modulus (CM) type or of the decisiondirected (DD) type, we derive normalized stochastic gradient algorithms for blind linear equalization (BE) of QAM systems. These algorithms allow us to formulate CM and DD separation principles, which help obtain a whole family of CM or DD BE algorithms from classical adaptive ltering algorithms. We focus on the algorithms obtained by using the A ne Projection adaptive ltering Algorithm (APA). Their increased convergence speed and ability to escape from local minima of their cost function, make these algorithms very promising for BE applications.
International Symposium on Information Theory, 2005
In this paper we derive the optimal diversity versus multiplexing tradeoff for a frequency select... more In this paper we derive the optimal diversity versus multiplexing tradeoff for a frequency selective i.i.d. Rayleigh MIMO channel. This tradeoff is shown to be better than the one of the frequency flat MIMO channel. Traditional approaches for frequency selective channels use OFDM techniques in order to exploit the diversity gain due to frequency selectivity. We show that although coding in OFDM over a sufficient subset of subcarriers allows to exploit full diversity as such (at fixed rate), such an approach leads to a suboptimal diversity vs multiplexing tradeoff.
This paper presents the impact of frequency diversity on the optimum expected end-to-end distorti... more This paper presents the impact of frequency diversity on the optimum expected end-to-end distortion (EED) in an outage-free wideband multiple-input multiple-output (MIMO) system. We provide the closed-form expression of optimum asymptotic expected EED comprised of the optimum distortion exponent and the multiplicative optimum distortion factor for high signal-to-noise ratio (SNR). It is shown that frequency diversity can improve EED though it has no effect on ergodic capacity. The improvement becomes slight when the frequency diversity order is greater than a certain number. The lower bounds related to infinite frequency diversity are derived. The results for outagefree systems are the bounds for outage-suffering systems and they are instructive for system design.
One of the most known classes of algorithms for blind equalization is the so-called class of Cons... more One of the most known classes of algorithms for blind equalization is the so-called class of Constant Modulus Algorithms (CMA's) [1], [2]. These adaptive algorithms use an instantaneous gradient-search procedure similar to that of the LMS algorithm in order to minimize a stochastic criterion that penalizes the deviations of the received signal's modulus with respect to the known modulus of the emitted input signal. However, as has been recently reported [4], [5], [6], [7], these algorithms might ill-converge if they are not properly initialized, due to false minima of their corresponding cost function. This holds even in cases where the equalizer can match exactly the inverse of the transmitting channel [6]. Recently, a variant of CMA algorithms, the so-called Normalized CMA (NCMA) has been introduced in [8] and a more general class of normalized CMA algorithms containing NCMA as its first member has been introduced in [11]. These algorithms have a stable operation for any...
2021 3rd IEEE Middle East and North Africa COMMunications Conference (MENACOMM), 2021
Thanks to the recent development of antenna design, localization based on the Direction of Arriva... more Thanks to the recent development of antenna design, localization based on the Direction of Arrival (DoA) of the incident signals is becoming more and more promising approach. This paper presents a direction-based positioning algorithm which can be implemented at the mobile device in 3D schemes. As the mobile orientation is unclear and inconstant, an algorithm utilizing the Direction Difference of Arrival (DDoA) among the incident signals is considered. Because of the complexity in computation, we use the Time of Arrival (ToA) as the additional data for position estimation. As a result, the joint DDoA-ToA method is studied. Moreover, an iterative Maximum Likelihood (ML) estimator for position estimation is presented to rectify the final estimates. Simulation results show significant performance improvement compared to other methods.
Employing dynamic Time Division Duplexing (DynTDD) can increase the system-wide spectral efficien... more Employing dynamic Time Division Duplexing (DynTDD) can increase the system-wide spectral efficiency of scenarios with varying and unbalanced uplink (UL) and downlink (DL) data traffic requirements. However when using DynTDD, a different DL/UL slot configuration is likely to be selected by neighboring cells, leading to Cross Link Interference (CLI) between the Base Stations (BS), which is known as BS-to-BS or DLto-UL interference, and between User Equipments (UE) which is known as UE-to-UE or UL-to-DL interference. Rank deficient channels are frequently encountered in Multi-Input Multi-Output (MIMO) networks, due to poor scattering and keyhole effects, or when using Massive MIMO and moving to mmWave. While the implications of rank deficient channels are well understood for the single user point to point setting, less is known for interference networks. In this paper we study the Degrees of Freedom (DoF) focusing on the UE-to-UE interference, by establishing necessary conditions, for ...
The communication between a multiple-antenna transmitter and multiple receivers (users) with eith... more The communication between a multiple-antenna transmitter and multiple receivers (users) with either a single or multiple-antenna each can be significantly enhanced by providing the channel state information at the transmitter (CSIT) of the users, as this allows for scheduling, beamforming and multiuser multiplexing gains. The traditional view on how to enable CSIT has been as follows so far: In time-division duplexed (TDD) systems, uplink (UL) and downlink (DL) channel reciprocity allows the use of a training sequence in the UL direction, which is exploited to obtain an UL channel estimate. This estimate is in turn recycled in the next downlink slot. In frequency-division duplexed (FDD) systems, which lack the UL and DL reciprocity, the CSIT is provided via the use of a dedicated feedback link of limited capacity between the receivers and the transmitter. In this paper, we focus on TDD systems and put this classical approach in question. In particular, we show that the traditional T...
HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific ... more HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci-entific research documents, whether they are pub-lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et a ̀ la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. 1 2
2010 IEEE Global Telecommunications Conference GLOBECOM 2010, 2010
This paper considers a large multiuser time-division duplex (TDD) system, where the base station ... more This paper considers a large multiuser time-division duplex (TDD) system, where the base station (BS) acquires channel state information via pilot signaling from the users. In the downlink the BS employs zero-forcing (ZF) and regularized zero-forcing (RZF) precoding. We derive the optimal sum rate maximizing amount of channel training using sum rate approximations from the large system analysis of MISO downlink channels under (R)ZF precoding. Moreover, in the regime of high signal-to-noise ratio (SNR), we derive approximate solutions of the optimal amount of training for both schemes that are of closed-form. By comparing the two schemes, we find that RZF requires less training than ZF, but the training interval of both schemes is equal for asymptotically high SNR. Furthermore, simulations are carried out which demonstrate the accuracy of our approximate solutions.
2007 IEEE Wireless Communications and Networking Conference, 2007
The problem of joint linear beamforming and scheduling in a MIMO broadcast channel is considered.... more The problem of joint linear beamforming and scheduling in a MIMO broadcast channel is considered. We show how Orthogonal Linear Beamforming (OLBF) can be efficiently combined with a low-complexity user selection algorithm to achieve a large portion of the multiuser capacity. The use of orthogonal transmission enables the transmitter to calculate exact signal-to-interference plus noise ratio (SINR) values during the user selection process. The knowledge of multiuser interference proves to be of particular importance for user scheduling as both the number of users in the cell and the average signal-tonoise ratio (SNR) decrease. The sum capacity of our scheme is characterized in the low-SNR regime, providing analytical results on the performance gain over Zero-Forcing Beamforming (ZFBF). Numerical results show gains over both suboptimal and optimal ZFBF techniques in different scenarios.
GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference, 2009
The communication between a multiple-antenna transmitter and multiple receivers (users) with eith... more The communication between a multiple-antenna transmitter and multiple receivers (users) with either a single or multiple-antenna each can be significantly enhanced by providing the channel state information at the transmitter (CSIT) of the users, as this allows for scheduling, beamforming and multiuser multiplexing gains. The traditional view on how to enable CSIT has been as follows so far: In time-division duplexed (TDD) systems, uplink (UL) and downlink (DL) channel reciprocity allows for the use of a training sequence in any given uplink slot, which is exploited to obtain an uplink channel estimate. This estimate is in turn recycled in the next downlink slot. In frequency-division duplexed (FDD) systems, which lack the UL and DL reciprocity, the CSIT is provided via the use of a dedicated feedback link of limited capacity between the receivers and the transmitter. In this paper, we focus on TDD systems and show that the traditional TDD CSIT acquisition fails to fully exploit the channel reciprocity in its true sense. In fact, we show that the system can benefit from a combined CSIT acquisition strategy mixing the use of limited feedback and that of a training sequence. We demonstrate the potential of our approach in terms of improved CSIT quality under a global training and feedback resource constraint.
2012 International Symposium on Wireless Communication Systems (ISWCS), 2012
We present in this paper a software implementation of a cognitive radio (CR) communication based ... more We present in this paper a software implementation of a cognitive radio (CR) communication based on long term evolution-time division duplex (LTE-TDD) channel reciprocity. We study the problem of calibration and beamforming design for a CR system in which a multiple-input single-output (MISO) secondary link, wants to opportunistically communicate without harming the primary SISO system. Specifically, we evaluate the CR communication through the EURECOM's experimental OpenAirInterface (OAI) software platform. We will show that it is feasible to restore the reciprocity after calibration in a non reciprocal channel, and provide an overview of challenges in the channel estimation for real conditions.
We propose an iterative algorithm to design optimal linear transmitters and receivers in a K-user... more We propose an iterative algorithm to design optimal linear transmitters and receivers in a K-user frequency-flat MIMO Interference Channel (MIMO IFC) with full channel state information (CSI). The transmitters and receivers are optimized to maximize the Weighted Sum Rate (WSR) of the MIMO IFC. Maximization of WSR is desirable since it allows the system to cover all the rate tuples on the Pareto-optimal rate region boundary for a given MIMO IFC. The proposed algorithm is rooted in a recent result [1] showing a correspondence between local optima of the Minimum Weighted Sum Mean Squared Error (MWSMSE) and Maximum Weighted Sum Rate (MWSR) objective functions for the MIMO Broadcast Channel (BC). This connection between the MWSR and MWSMSE is shown to hold true also in the MIMO IFC and is exploited to design an alternating minimization algorithm for MIMO IFC that maximizes the WSR. The MWSMSE-MWSR connection also allows to solve the transmit filter design subproblem in the alternating algorithm by invoking a heuristic solution first proposed in [2],[3]. Another contribution of this paper is to propose an extension of [4] to MIMO problems, following the philosophy of [1] in part. This path is shown to lead in fact to the same iterative algorithm, showing the optimality of the heuristic of [2],[3] when applied in the context of the alternating transmitter-receiver optimization approach of [1].
The communication between a multiple-antenna transmitter and multiple receivers (users) with eith... more The communication between a multiple-antenna transmitter and multiple receivers (users) with either a single or multiple-antenna each can be significantly enhanced by providing the channel state information at the transmitter (CSIT) of the users, as this allows for scheduling, beamforming and multiuser multiplexing gains. The traditional view on how to enable CSIT has been as follows so far: In time-division duplexed (TDD) systems, uplink (UL) and downlink (DL) channel reciprocity allows the use of a training sequence in the UL direction, which is exploited to obtain an UL channel estimate. This estimate is in turn recycled in the next downlink slot. In frequency-division duplexed (FDD) systems, which lack the UL and DL reciprocity, the CSIT is provided via the use of a dedicated feedback link of limited capacity between the receivers and the transmitter. In this paper, we focus on TDD systems and put this classical approach in question. In particular, we show that the traditional TDD setup above fails to fully exploit the channel reciprocity in its true sense. In fact, we show that the system can benefit from a combined CSIT acquisition strategy mixing the use of limited feedback and that of a training sequence. This combining gives rise to a very interesting joint estimation and detection problem for which we propose two iterative algorithms. An outage rate based framework is also developed which gives the optimal resource split between training and feedback. We demonstrate the potential of this hybrid combining in terms of the improved CSIT quality under a global training and feedback resource constraint.
By minimizing a deterministic criterion of the constant modulus (CM) type or of the decisiondirec... more By minimizing a deterministic criterion of the constant modulus (CM) type or of the decisiondirected (DD) type, we derive normalized stochastic gradient algorithms for blind linear equalization (BE) of QAM systems. These algorithms allow us to formulate CM and DD separation principles, which help obtain a whole family of CM or DD BE algorithms from classical adaptive ltering algorithms. We focus on the algorithms obtained by using the A ne Projection adaptive ltering Algorithm (APA). Their increased convergence speed and ability to escape from local minima of their cost function, make these algorithms very promising for BE applications.
International Symposium on Information Theory, 2005
In this paper we derive the optimal diversity versus multiplexing tradeoff for a frequency select... more In this paper we derive the optimal diversity versus multiplexing tradeoff for a frequency selective i.i.d. Rayleigh MIMO channel. This tradeoff is shown to be better than the one of the frequency flat MIMO channel. Traditional approaches for frequency selective channels use OFDM techniques in order to exploit the diversity gain due to frequency selectivity. We show that although coding in OFDM over a sufficient subset of subcarriers allows to exploit full diversity as such (at fixed rate), such an approach leads to a suboptimal diversity vs multiplexing tradeoff.
This paper presents the impact of frequency diversity on the optimum expected end-to-end distorti... more This paper presents the impact of frequency diversity on the optimum expected end-to-end distortion (EED) in an outage-free wideband multiple-input multiple-output (MIMO) system. We provide the closed-form expression of optimum asymptotic expected EED comprised of the optimum distortion exponent and the multiplicative optimum distortion factor for high signal-to-noise ratio (SNR). It is shown that frequency diversity can improve EED though it has no effect on ergodic capacity. The improvement becomes slight when the frequency diversity order is greater than a certain number. The lower bounds related to infinite frequency diversity are derived. The results for outagefree systems are the bounds for outage-suffering systems and they are instructive for system design.
One of the most known classes of algorithms for blind equalization is the so-called class of Cons... more One of the most known classes of algorithms for blind equalization is the so-called class of Constant Modulus Algorithms (CMA's) [1], [2]. These adaptive algorithms use an instantaneous gradient-search procedure similar to that of the LMS algorithm in order to minimize a stochastic criterion that penalizes the deviations of the received signal's modulus with respect to the known modulus of the emitted input signal. However, as has been recently reported [4], [5], [6], [7], these algorithms might ill-converge if they are not properly initialized, due to false minima of their corresponding cost function. This holds even in cases where the equalizer can match exactly the inverse of the transmitting channel [6]. Recently, a variant of CMA algorithms, the so-called Normalized CMA (NCMA) has been introduced in [8] and a more general class of normalized CMA algorithms containing NCMA as its first member has been introduced in [11]. These algorithms have a stable operation for any...
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