Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/1257
2017-03-27T15:00:24ZCancellation of external and multiple access interference in cdma systems using antenna arrays
http://hdl.handle.net/2117/102883
Cancellation of external and multiple access interference in cdma systems using antenna arrays
Muñoz Medina, Olga; Fernández Rubio, Juan Antonio
This paper deals with the problem of multisensor-multiuser detection in CDMA systems in the presence of interferences external to the system. The paper presents a new method able to estimate the spatial signature of all active users projected onto the subspace orthogonal to the external interference. With this information a specific beamformer can be designed for each user in order to combat the external and multiple access interference. The method performs in frequency non-selective multipath scenarios as they arise from some CDMA satellite and indoor communications systems. The estimation process does not require any training signal nor any a priori spatial information. It exploits the temporal structure of CDMA signals and extract the required information directly from the received signals. In addition, the method is independent of the nature of the external interference and it can cope with narrow-band and wide-band interfering signals.
2017-03-24T16:35:31ZMuñoz Medina, OlgaFernández Rubio, Juan AntonioThis paper deals with the problem of multisensor-multiuser detection in CDMA systems in the presence of interferences external to the system. The paper presents a new method able to estimate the spatial signature of all active users projected onto the subspace orthogonal to the external interference. With this information a specific beamformer can be designed for each user in order to combat the external and multiple access interference. The method performs in frequency non-selective multipath scenarios as they arise from some CDMA satellite and indoor communications systems. The estimation process does not require any training signal nor any a priori spatial information. It exploits the temporal structure of CDMA signals and extract the required information directly from the received signals. In addition, the method is independent of the nature of the external interference and it can cope with narrow-band and wide-band interfering signals.Experimental result for a sdma mobile communications antenna array system
http://hdl.handle.net/2117/102879
Experimental result for a sdma mobile communications antenna array system
Goldberg, Jason Matthew; Pagès Zamora, Alba Maria; Lagunas Hernandez, Miguel A.; Rodríguez Fonollosa, Javier; Vázquez Grau, Gregorio
This paper presents experimental results for a Spatial
Division Multiple Access cellular mobile communications
system. The basestation antenna array testbed
used to obtain the results is described in addition to
sophisticated signal processing algorithms applied to
the received data. These algorithms perform source
tracking, beamforming for noise and interference reduction,
and data detection. Simple experiments involving
multiple co-channel users have been performed
and results are presented in terms of output bit error
rate. These results show that SDMA may be a technically
feasible way to increase the spectrum efficiency of
cellular mobile communications networks.
2017-03-24T14:09:29ZGoldberg, Jason MatthewPagès Zamora, Alba MariaLagunas Hernandez, Miguel A.Rodríguez Fonollosa, JavierVázquez Grau, GregorioThis paper presents experimental results for a Spatial
Division Multiple Access cellular mobile communications
system. The basestation antenna array testbed
used to obtain the results is described in addition to
sophisticated signal processing algorithms applied to
the received data. These algorithms perform source
tracking, beamforming for noise and interference reduction,
and data detection. Simple experiments involving
multiple co-channel users have been performed
and results are presented in terms of output bit error
rate. These results show that SDMA may be a technically
feasible way to increase the spectrum efficiency of
cellular mobile communications networks.Blind multiuser detection using hidden markov models theory
http://hdl.handle.net/2117/102833
Blind multiuser detection using hidden markov models theory
Antón Haro, Carles; Rodríguez Fonollosa, José Adrián; Rodríguez Fonollosa, Javier
We present an adaptive algorithm based on the theory of hidden Markov models (HMM) which is capable of jointly detecting the users in a DS-CDMA system. The proposed technique is near-far resistant and completely blind in the sense that no knowledge of the signature sequences, channel state information or training sequences is required for any user. In addition to this, an estimate of the signature of each user convolved with its physical channel impulse response (CIR), and an estimate of the background noise variance are provided once convergence is achieved (as well as estimated data sequences). At this moment, and using that CIR estimate, we can switch to any decision-directed (DD) adaptation scheme.
2017-03-23T15:04:02ZAntón Haro, CarlesRodríguez Fonollosa, José AdriánRodríguez Fonollosa, JavierWe present an adaptive algorithm based on the theory of hidden Markov models (HMM) which is capable of jointly detecting the users in a DS-CDMA system. The proposed technique is near-far resistant and completely blind in the sense that no knowledge of the signature sequences, channel state information or training sequences is required for any user. In addition to this, an estimate of the signature of each user convolved with its physical channel impulse response (CIR), and an estimate of the background noise variance are provided once convergence is achieved (as well as estimated data sequences). At this moment, and using that CIR estimate, we can switch to any decision-directed (DD) adaptation scheme.New bounds on RAKE structures for DS-CDMA over frequency-selective Rayleigh fading channels
http://hdl.handle.net/2117/102811
New bounds on RAKE structures for DS-CDMA over frequency-selective Rayleigh fading channels
Calvo Zorrilla, Sergio; Vázquez Grau, Gregorio
An upper bound is derived for the probability of error in an asynchronous binary direct-sequence spread-spectrum multiple-access communications system operating over frequency selective Rayleigh fading channels. A coherent RAKE receiver with predetection selective diversity combining is considered. The performance of a multipath-combining receiver is determined for the case of multiple interfering transmitters. Furthermore, the performance of the system is determined in terms of parameters of the signature sequences. These parameters can be used as guides in selecting sequences for the system. The bounds agree with the exponential portion of a normal distribution in which the interfering interference components subtract from the signal amplitude. The results obtained are verified by simulation.
2017-03-22T16:53:29ZCalvo Zorrilla, SergioVázquez Grau, GregorioAn upper bound is derived for the probability of error in an asynchronous binary direct-sequence spread-spectrum multiple-access communications system operating over frequency selective Rayleigh fading channels. A coherent RAKE receiver with predetection selective diversity combining is considered. The performance of a multipath-combining receiver is determined for the case of multiple interfering transmitters. Furthermore, the performance of the system is determined in terms of parameters of the signature sequences. These parameters can be used as guides in selecting sequences for the system. The bounds agree with the exponential portion of a normal distribution in which the interfering interference components subtract from the signal amplitude. The results obtained are verified by simulation.On the inclusion of channel's time dependence in a hidden Markov model for blind channel estimation
http://hdl.handle.net/2117/102804
On the inclusion of channel's time dependence in a hidden Markov model for blind channel estimation
Antón Haro, Carles; Rodríguez Fonollosa, José Adrián; Rodríguez Fonollosa, Javier
We introduce several modifications to the Baum&Welch (BW) formulas used to reestimate the parameters of a hidden Markov model (HMM). The estimated parameter is the channel impulse response (CIR) of a communication system which is known to be time-varying. With these modifications, channel tracking properties of a BW-based algorithm are improved. The resulting algorithm is tested in a specific mobile radio environment (the GSM system), exhibiting good performance at expenses of higher computational complexity.
2017-03-22T14:38:06ZAntón Haro, CarlesRodríguez Fonollosa, José AdriánRodríguez Fonollosa, JavierWe introduce several modifications to the Baum&Welch (BW) formulas used to reestimate the parameters of a hidden Markov model (HMM). The estimated parameter is the channel impulse response (CIR) of a communication system which is known to be time-varying. With these modifications, channel tracking properties of a BW-based algorithm are improved. The resulting algorithm is tested in a specific mobile radio environment (the GSM system), exhibiting good performance at expenses of higher computational complexity.Robust data detection in asynchronous DS-CDMA in the presence of timing uncertainty
http://hdl.handle.net/2117/102802
Robust data detection in asynchronous DS-CDMA in the presence of timing uncertainty
Riba Sagarra, Jaume; Goldberg, J; Vázquez Grau, Gregorio
The decorrelating and minimum mean squared error data detectors for direct sequence code division multiple access (DS-CDMA) communications systems are known to exhibit low vulnerability to the near-far problem. Nevertheless, the performance of these algorithms is highly sensitive to an accurate knowledge of the user propagation delays as well as inter-symbol and/or inter-chip interference such as that produced by frequency-selective fading channels. A new sub-optimum symbol-by-symbol detector is presented which is robust in the presence of these two effects.
2017-03-22T14:26:48ZRiba Sagarra, JaumeGoldberg, JVázquez Grau, GregorioThe decorrelating and minimum mean squared error data detectors for direct sequence code division multiple access (DS-CDMA) communications systems are known to exhibit low vulnerability to the near-far problem. Nevertheless, the performance of these algorithms is highly sensitive to an accurate knowledge of the user propagation delays as well as inter-symbol and/or inter-chip interference such as that produced by frequency-selective fading channels. A new sub-optimum symbol-by-symbol detector is presented which is robust in the presence of these two effects.Channel estimation for transform modulations in mobile communications
http://hdl.handle.net/2117/102800
Channel estimation for transform modulations in mobile communications
Lamarca Orozco, M. Meritxell; Vázquez Grau, Gregorio
This paper deals with data-aided channel estimation in systems using OFDM modulation. We formulate a pilot symbol-based channel estimator and compare it with the pilot-tone one proposed in [1]. Although this paper focuses in flat fading mobile channels, the results could easily be applied to OFDM systems operating in frequency-selective channels.
2017-03-22T13:19:59ZLamarca Orozco, M. MeritxellVázquez Grau, GregorioThis paper deals with data-aided channel estimation in systems using OFDM modulation. We formulate a pilot symbol-based channel estimator and compare it with the pilot-tone one proposed in [1]. Although this paper focuses in flat fading mobile channels, the results could easily be applied to OFDM systems operating in frequency-selective channels.Symbol decoding based on signal subspace decomposition in msk
http://hdl.handle.net/2117/102676
Symbol decoding based on signal subspace decomposition in msk
Ruiz Feliu, Rafael; Cabrera Beán, Margarita Asuncion
The availability of fast processors with architectures tailored to meet the computational demand of digital signal processing algorithms is widely applied to demodulation and decodification of CPM signals in some scenes: Mobiles, AWGN channels,… In this application the number of floating point operations executed by each processed symbol is a critical parameter to be designed, this is to be minimized. In this paper a method that reduces significantly the number of operations (until 80%) by symbol for CPM signals is presented. The decodification stage is performed from the rank reduced signal subspace obtained by means of an orthogonal decomposition of the signal [1].
2017-03-20T15:36:46ZRuiz Feliu, RafaelCabrera Beán, Margarita AsuncionThe availability of fast processors with architectures tailored to meet the computational demand of digital signal processing algorithms is widely applied to demodulation and decodification of CPM signals in some scenes: Mobiles, AWGN channels,… In this application the number of floating point operations executed by each processed symbol is a critical parameter to be designed, this is to be minimized. In this paper a method that reduces significantly the number of operations (until 80%) by symbol for CPM signals is presented. The decodification stage is performed from the rank reduced signal subspace obtained by means of an orthogonal decomposition of the signal [1].Duration modeling with expanded HMM applied to speech recognition
http://hdl.handle.net/2117/102630
Duration modeling with expanded HMM applied to speech recognition
Bonafonte Cávez, Antonio; Vidal Manzano, José; Nogueiras Rodríguez, Albino
The occupancy of the HMM states is modeled by means of a Markov chain. A linear estimator is introduced to compute the probabilities of the Markov chain. The distribution function (DF) represents accurately the observed data. Representing the DF as a Markov chain allows the use of standard HMM recognizers. The increase of complexity is negligible in training and strongly limited during recognition. Experiments performed on acoustic-phonetic decoding shows how the phone recognition rate increases from 60.6 to 61.1. Furthermore, on a task of database inquires, where phones are used as subword units, the correct word rate increases from 88.2 to 88.4.
2017-03-17T16:30:51ZBonafonte Cávez, AntonioVidal Manzano, JoséNogueiras Rodríguez, AlbinoThe occupancy of the HMM states is modeled by means of a Markov chain. A linear estimator is introduced to compute the probabilities of the Markov chain. The distribution function (DF) represents accurately the observed data. Representing the DF as a Markov chain allows the use of standard HMM recognizers. The increase of complexity is negligible in training and strongly limited during recognition. Experiments performed on acoustic-phonetic decoding shows how the phone recognition rate increases from 60.6 to 61.1. Furthermore, on a task of database inquires, where phones are used as subword units, the correct word rate increases from 88.2 to 88.4.Blind multiuser deconvolution in fading and dispersive channels
http://hdl.handle.net/2117/102596
Blind multiuser deconvolution in fading and dispersive channels
Rodríguez Fonollosa, Javier; Rodríguez Fonollosa, José Adrián; Zvonar, Z; Vidal Manzano, José
An adaptive near-far resistant technique for the blind joint multiuser identification and detection in asynchronous CDMA systems is analyzed in fading and dispersive GSM channels.
2017-03-16T14:23:01ZRodríguez Fonollosa, JavierRodríguez Fonollosa, José AdriánZvonar, ZVidal Manzano, JoséAn adaptive near-far resistant technique for the blind joint multiuser identification and detection in asynchronous CDMA systems is analyzed in fading and dispersive GSM channels.