Daniel Munoz - Academia.edu (original) (raw)

Papers by Daniel Munoz

IEEE Transactions on Vehicular Technology, 2015

Most of the relaying strategies exploit channel state information (CSI), but there exist only a f... more Most of the relaying strategies exploit channel state information (CSI), but there exist only a few limited works on acquisition of the required CSI. In this paper we present general protocols and pilot designs for CSI acquisition in different types of relay systems using multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) transmission. We propose new pilot forwarding mechanisms and a related estimator for obtaining CSIs of individual MIMO channels of cascaded links at the end node(s). We develop new pilot designs with low overhead for channels with different lengths. We present several CSI acquisition protocols for relay MIMO systems with time division duplexing (TDD) as well as frequency division duplexing (FDD). We introduce node multiplexing which reduces overhead and delay for pilot or CSI feedback transmissions from multiple nodes. In addition, we present similar CSI acquisition protocols for multi-point to multi-point systems while keeping overhead low. Simulation results are included to demonstrate the estimation performance of our proposed designs. Discussions on several protocol options are also provided.

2009 IEEE 70th Vehicular Technology Conference Fall, 2009

All practical OFDM systems insert null guard bands to facilitate easy filter implementation and e... more All practical OFDM systems insert null guard bands to facilitate easy filter implementation and emission spectrum control. The null guard bands introduce a constraint for optimal pilot designs in MIMO OFDM systems. Semiconductor downscaling and the use of high modulation order have signified the importance of pilot designs for OFDM systems in the presence of I/Q imbalances, but existing designs have not addressed the use of guard bands, the overhead efficiency, the estimation optimality, and general applicability in pilot data multiplexed format and/or MIMO setup. This paper proposes a pilot design for channel estimation of MIMO OFDM systems with guard bands and both transmit and receive frequency-dependent I/Q imbalances, which overcomes the limitations of the existing designs. Simulation and numerical results corroborate better performance, overhead advantage and applicability in pilot-data-multiplexed MIMO setup of the proposed design over the existing MIMO OFDM pilot design with I/Q imbalances.

GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference, 2009

Efficient pilot designs are vital as they improve system performance and resource utilization, es... more Efficient pilot designs are vital as they improve system performance and resource utilization, especially in multiinput multi-output (MIMO) orthogonal frequency divison multiplexing (OFDM) systems. Most of the existing pilot designs do not consider in-phase and quadrature (I/Q) imbalance whose detrimental effects become more severe since the technology and applications are pushing towards smaller semiconductor node, smaller chip, cheaper equipment, and larger modulation order. This paper studies the impact of I/Q imbalance on the pilot designs, and presents several new pilot designs for equivalent channel estimation of MIMO OFDM systems with frequencydependent I/Q imbalances. Advantages of the proposed designs are illustrated through simulation and analytical results in terms of estimation accuracy, error rate, overhead efficiency, and generality with the transmission formats (preamble-based or pilot-data-multiplexed systems, with or without null guard tones).

IEEE Wireless Communications Letters, 2012

We consider multi-input multi-output (MIMO) antennas relay systems under time-varying channels an... more We consider multi-input multi-output (MIMO) antennas relay systems under time-varying channels and propose a joint relay, antenna, subband, and MIMO transmission mode adaptation scheme which enables antenna selection to exploit channel state information (CSI) at the beginning of transmission and switch to space-frequency block coding (SFBC) when CSI becomes outdated. Moreover, we propose temporal power and bit loading for the cascaded source-relay-destination link with/without inter-hop power allocation to further enhance the system performance.

IEEE Transactions on Communications, 2010

IEEE Communications Letters, 2012

We consider a relay clustering system using decode and forward (DF) relaying, orthogonal frequenc... more We consider a relay clustering system using decode and forward (DF) relaying, orthogonal frequency division multiplexing (OFDM), and transmit maximal ratio combining beamforming (TMRC-BF) at the relays. We address channel estimation at the destination for the above system. A cluster pairing scheme with corresponding pilot designs is proposed. It reduces both necessary pilot overhead and computational complexity by half. Simulation results show that if the signal to noise ratio (SNR) of pilots for channel estimation for TMRC-BF at the relays is kept above a threshold (5 dB below the SNR of the pilots sent to the destination by the cluster pairing strategy), nearly optimal channel estimation performance can be achieved.

IEEE Transactions on Vehicular Technology, 2015

Most of the relaying strategies exploit channel state information (CSI), but there exist only a f... more Most of the relaying strategies exploit channel state information (CSI), but there exist only a few limited works on acquisition of the required CSI. In this paper we present general protocols and pilot designs for CSI acquisition in different types of relay systems using multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) transmission. We propose new pilot forwarding mechanisms and a related estimator for obtaining CSIs of individual MIMO channels of cascaded links at the end node(s). We develop new pilot designs with low overhead for channels with different lengths. We present several CSI acquisition protocols for relay MIMO systems with time division duplexing (TDD) as well as frequency division duplexing (FDD). We introduce node multiplexing which reduces overhead and delay for pilot or CSI feedback transmissions from multiple nodes. In addition, we present similar CSI acquisition protocols for multi-point to multi-point systems while keeping overhead low. Simulation results are included to demonstrate the estimation performance of our proposed designs. Discussions on several protocol options are also provided.

2009 IEEE 70th Vehicular Technology Conference Fall, 2009

All practical OFDM systems insert null guard bands to facilitate easy filter implementation and e... more All practical OFDM systems insert null guard bands to facilitate easy filter implementation and emission spectrum control. The null guard bands introduce a constraint for optimal pilot designs in MIMO OFDM systems. Semiconductor downscaling and the use of high modulation order have signified the importance of pilot designs for OFDM systems in the presence of I/Q imbalances, but existing designs have not addressed the use of guard bands, the overhead efficiency, the estimation optimality, and general applicability in pilot data multiplexed format and/or MIMO setup. This paper proposes a pilot design for channel estimation of MIMO OFDM systems with guard bands and both transmit and receive frequency-dependent I/Q imbalances, which overcomes the limitations of the existing designs. Simulation and numerical results corroborate better performance, overhead advantage and applicability in pilot-data-multiplexed MIMO setup of the proposed design over the existing MIMO OFDM pilot design with I/Q imbalances.

GLOBECOM 2009 - 2009 IEEE Global Telecommunications Conference, 2009

Efficient pilot designs are vital as they improve system performance and resource utilization, es... more Efficient pilot designs are vital as they improve system performance and resource utilization, especially in multiinput multi-output (MIMO) orthogonal frequency divison multiplexing (OFDM) systems. Most of the existing pilot designs do not consider in-phase and quadrature (I/Q) imbalance whose detrimental effects become more severe since the technology and applications are pushing towards smaller semiconductor node, smaller chip, cheaper equipment, and larger modulation order. This paper studies the impact of I/Q imbalance on the pilot designs, and presents several new pilot designs for equivalent channel estimation of MIMO OFDM systems with frequencydependent I/Q imbalances. Advantages of the proposed designs are illustrated through simulation and analytical results in terms of estimation accuracy, error rate, overhead efficiency, and generality with the transmission formats (preamble-based or pilot-data-multiplexed systems, with or without null guard tones).

IEEE Wireless Communications Letters, 2012

We consider multi-input multi-output (MIMO) antennas relay systems under time-varying channels an... more We consider multi-input multi-output (MIMO) antennas relay systems under time-varying channels and propose a joint relay, antenna, subband, and MIMO transmission mode adaptation scheme which enables antenna selection to exploit channel state information (CSI) at the beginning of transmission and switch to space-frequency block coding (SFBC) when CSI becomes outdated. Moreover, we propose temporal power and bit loading for the cascaded source-relay-destination link with/without inter-hop power allocation to further enhance the system performance.

IEEE Transactions on Communications, 2010

IEEE Communications Letters, 2012

We consider a relay clustering system using decode and forward (DF) relaying, orthogonal frequenc... more We consider a relay clustering system using decode and forward (DF) relaying, orthogonal frequency division multiplexing (OFDM), and transmit maximal ratio combining beamforming (TMRC-BF) at the relays. We address channel estimation at the destination for the above system. A cluster pairing scheme with corresponding pilot designs is proposed. It reduces both necessary pilot overhead and computational complexity by half. Simulation results show that if the signal to noise ratio (SNR) of pilots for channel estimation for TMRC-BF at the relays is kept above a threshold (5 dB below the SNR of the pilots sent to the destination by the cluster pairing strategy), nearly optimal channel estimation performance can be achieved.