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**1 - 7**of**7**### EURASIP Journal on Applied Signal Processing 2004:5, 727–739 c ○ 2004 Hindawi Publishing Corporation Maximum Likelihood Turbo Iterative Channel Estimation for Space-Time Coded Systems and Its Application to Radio Transmission in Subway Tunnels

, 2003

"... This paper presents a novel channel estimation technique for space-time coded (STC) systems. It is based on applying the maximum likelihood (ML) principle not only over a known pilot sequence but also over the unknown symbols in a data frame. The resulting channel estimator gathers both the determin ..."

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This paper presents a novel channel estimation technique for space-time coded (STC) systems. It is based on applying the maximum likelihood (ML) principle not only over a known pilot sequence but also over the unknown symbols in a data frame. The resulting channel estimator gathers both the deterministic information corresponding to the pilot sequence and the statistical information, in terms of a posteriori probabilities, about the unknown symbols. The method is suitable for Turbo equalization schemes where those probabilities are computed with more and more precision at each iteration. Since the ML channel estimation problem does not have a closed-form solution, we employ the expectation-maximization (EM) algorithm in order to iteratively compute the ML estimate. The proposed channel estimator is first derived for a general time-dispersive MIMO channel and then is particularized to a realistic scenario consisting of a transmission system based on the global system mobile (GSM) standard performing in a subway tunnel. In this latter case, the channel is nondispersive but there exists controlled ISI introduced by the Gaussian minimum shift keying (GMSK) modulation format used in GSM. We demonstrate, using experimentally measured channels, that the training sequence length can be reduced from 26 bits as in the GSM standard to only 5 bits, thus achieving a 14 % improvement in system throughput.

### EURASIP Journal on Applied Signal Processing 2004:5, 727–739 c ⃝ 2004 Hindawi Publishing Corporation Maximum Likelihood Turbo Iterative Channel Estimation for Space-Time Coded Systems and Its Application to Radio Transmission in Subway Tunnels

, 2003

"... This paper presents a novel channel estimation technique for space-time coded (STC) systems. It is based on applying the max-imum likelihood (ML) principle not only over a known pilot sequence but also over the unknown symbols in a data frame. The resulting channel estimator gathers both the determi ..."

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This paper presents a novel channel estimation technique for space-time coded (STC) systems. It is based on applying the max-imum likelihood (ML) principle not only over a known pilot sequence but also over the unknown symbols in a data frame. The resulting channel estimator gathers both the deterministic information corresponding to the pilot sequence and the statistical information, in terms of a posteriori probabilities, about the unknown symbols. The method is suitable for Turbo equalization schemes where those probabilities are computed with more and more precision at each iteration. Since the ML channel estimation problem does not have a closed-form solution, we employ the expectation-maximization (EM) algorithm in order to iteratively compute the ML estimate. The proposed channel estimator is first derived for a general time-dispersive MIMO channel and then is particularized to a realistic scenario consisting of a transmission system based on the global system mobile (GSM) standard performing in a subway tunnel. In this latter case, the channel is nondispersive but there exists controlled ISI introduced by the Gaussian minimum shift keying (GMSK) modulation format used in GSM. We demonstrate, using experimentally measured channels, that the training sequence length can be reduced from 26 bits as in the GSM standard to only 5 bits, thus achieving a 14 % improvement in system throughput.

### BER Performance Evaluation of GMSK for Fading Mobile Channels

"... Abstract — Digital modulation plays a significant role in efficient wireless communication. It allows the transmission of digital data via air on high frequency carrier waves. The worst case communication channel is usually in the urban environment where there are many obstacles. Due to the obstacle ..."

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Abstract — Digital modulation plays a significant role in efficient wireless communication. It allows the transmission of digital data via air on high frequency carrier waves. The worst case communication channel is usually in the urban environment where there are many obstacles. Due to the obstacles and reflectors, the transmitted signal arrives at the receiver from various directions over a multiplicity of paths. Such a phenomenon is called multipath. Mobile radio propagation is characterized by three main aspects: fading, shadowing and path loss. A major concern in a cellular mobile radio system is the co-channel interference. Therefore, the reduction of co-channel interference becomes a main thrust for the system design engineers. GMSK is studied and identified as an effective digital modulation technique suitable for power and band-limited mobile radio. This paper evaluates the BER performance of GMSK system under different channel models i.e. AWGN, Rayleigh and Rician fading channels. Subsequently, a comparative study is carried out to obtain the BER performance for BPSK and QPSK under fading mobile channels. The comparative study showed that BER for BPSK and QPSK are similar and they give the lowest BER under multipath fading. Though BPSK and QPSK give slightly better BER performance than GMSK, the spectral efficiency and hence power efficiency advantages of GMSK make it the preferred choice of modulation in fading mobile channels.

### Wireless World Research Forum Working Group 6 White Paper Element management, flexible air interfaces, SDR Element Management, Flexible Air Interfaces, SDR

"... In today’s wireless world a large number of Radio Access Technology (RAT) standards is available. The recent trend of "wireless beyond the third generation " (B3G) assumes that cellular, Broadband Radio Access Networks (BRAN) / Wireless Local Area Networks (WLAN) and Digital Video ..."

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In today’s wireless world a large number of Radio Access Technology (RAT) standards is available. The recent trend of &quot;wireless beyond the third generation &quot; (B3G) assumes that cellular, Broadband Radio Access Networks (BRAN) / Wireless Local Area Networks (WLAN) and Digital Video Broadcasting (DVB) systems can be co-operating components of a Composite Radio (CR) infrastructure. Through such a CR system, that provides the possibility of co-operation among the various available RATs, users can be directed to the most appropriate one, according to the service area regions, time zones, profile and network performance criteria. In this context, the deployment of CR systems requires technologies that allow terminals and network elements to dynamically select and adapt to the most appropriate RAT (in a transparent manner). The Reconfigurability concept (which is an evolution of &quot;software defined radio&quot;) provides such technologies posing essential issues with respect to element management. In this direction, one of the targets of this white paper is to present a concept for a Management and Control System that enables elements to operate in an end-to-end reconfigurability context. The main idea of this concept is a clear separation of the management and the control functions. Hardware abstraction is a research topic widely discussed in the reconfigurability community (e.g. specific RFI in the SDR Forum). The paper

### A Model-Based . . . in a Cochannel Interference Limited Environment

, 2002

"... Cochannel interference (CCI) is a major impairment in narrowband cellular systems. To increase the spectral efficiency of the narrowband systems, identical carrier frequencies are reused in distant cells. The interference rejection capability of the receiver determines this frequency reuse and is t ..."

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Cochannel interference (CCI) is a major impairment in narrowband cellular systems. To increase the spectral efficiency of the narrowband systems, identical carrier frequencies are reused in distant cells. The interference rejection capability of the receiver determines this frequency reuse and is therefore critical. In this thesis, we propose an improved demodulation scheme, employing high-resolution frequency estimation techniques, for continuous phase modulated (CPM) signals in presence of CCI. Minimum shift keying (MSK), which is a special case of CPM, is a very popular modulation format around the world. Frequency detectors, such as the limiterdiscriminator permit the non-coherent demodulation of MSK signals. High- resolution frequency estimation appears as a very attractive alternative to the conventional noncoherent frequency detectors. The frequency estimation methods that we have studied are based on autoregressive modeling. The

### EURASIP Journal on Applied Signal Processing 2002:11, 1296–1300 c ○ 2002 Hindawi Publishing Corporation Loudspeaker Equalization with Post-Processing

, 2001

"... Loudspeaker equalization is an essential technique in audio system design. A well-known equalization scheme is based on the deconvolution of the desired equalized response with the measured impulse response of the loudspeaker. In this paper, a postprocessing scheme is combined with the deconvolution ..."

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Loudspeaker equalization is an essential technique in audio system design. A well-known equalization scheme is based on the deconvolution of the desired equalized response with the measured impulse response of the loudspeaker. In this paper, a postprocessing scheme is combined with the deconvolution-based algorithm to provide a better equalization effect. Computer simulation results are given to demonstrate the significant improvement that can be achieved using this method.