Michael Horvat

Closed loop transmission with precoding selection in LTE/LTE-Advanced system

Closed-loop transmission combined with MIMO (multiple-input multiple-output) and OFDM (orthogonal frequency division multiplexing) technologies have drawn most attentions during development of the 4G systems (fourth generation of mobile communication systems). In LTE (Long Term Evolution) and LTE-Advanced systems, which are proposed by 3GPP (Third Generation Partnership Project) to be the most competitive candidate for the 4G systems, the codebook based precoding scheme is deployed for realizing the closed-loop transmission concept. This scheme introduces the precoding matrix selection at the receiver and precoding operation at the transmitter and achieves a good tradeoff between the system complexity and the performance gain given by the closed-loop transmission. In this manuscript, the authors give a brief overview of the LTE/LTE-Advanced system downlink transmission. Furthermore, different precoding matrix selection criteria are discussed at the aim of optimal receiver design. Following the analytical and numerical results, the authors conclude that the minimum post mean squared error based criterion is the optimal candidate for precoding matrix selection at the receiver in LTE compliant systems.

On the physical layer performance with rank indicator selection in LTE/LTE-Advanced system

The 3GPP (Third Generation Partnership Project) LTE (Long Term Evolution) and LTE-Advanced activities work toward the evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access (E-UTRA), and the solution of IMT-Advanced (International Mobile Telecommunications) and systems beyond. The combination of OFDM (orthogonal frequency division multiplexing) and MIMO (multiple-input multiple-output) has been introduced into LTE and LTE-Advanced systems for achieving high system capacity. Furthermore, the closed-loop concept with codebook based precoding MIMO and transmission layers selection, termed as RI (rank indicator) selection have also been included to provide robust transmission in mobile wireless communication scenarios and increase the cell coverage. This manuscript focuses on the RI selection study and implementation in LTE and LTE-Advanced systems and illustrates the downlink performance evaluation and comparison with different RI selection schemes. According to the analytical and numerical results from an LTE and LTE-Advanced compliant simulator, the mutual information based scheme is chosen as the best candidate for RI selection.

Dynamic transmission mode selection in LTE/LTE-Advanced system

Recently, the LTE (Long Term Evolution) and LTE-Advanced systems, developed by the 3GPP (Third Generation Partnership Project), has been proposed as the candidate for the 4G systems (forth mobile communication systems). The combination of OFDM (orthogonal frequency division multiplexing) and MIMO (multiple-input multiple-output) transmission technologies has been introduced into LTE systems for achieving high system performance required by 4G systems. Furthermore, the closed-loop concept with codebook based precoding MIMO and dynamic transmission mode selection, termed as RI (rank indicator) selection, have also been deployed in LTE systems to provide robust link connection and large cell coverage. In this manuscript, the authors focused on the study of dynamic transmission mode selection and its implementation in LTE systems. Different RI selection schemes were proposed in this manuscript with the corresponding downlink performance evaluation. According to the analytical and numerical results, the authors conclude that the mutual information based scheme is the best candidate for RI selection in LTE/LTE-Advanced compliant systems.

Analytic performance evaluation of an LTE SFBC system with Wiener channel estimation

A closed-form expression of the uncoded error probabilities of a space-frequency block code employing an Alamouti Maximum Likelihood symbol detector with linear combining is derived. Our analysis is conducted in the framework of a Long Term Evolution air interface and accounts for the estimation error of an optimal Wiener channel interpolator. The optimal pilot spacing and filter length is evaluated for different power delay profiles through numerical and analytical results.

System performance of UTRA LTE and LTE-advanced

The long term evolution of UMTS Terrestrial Radio Access (UTRA LTE) and its enhanced version - LTE-Advanced use OFDM (orthogonal frequency division multiplexing) combined with MIMO (multiple-input multiple-output), termed MIMO-OFDM. The spatial multiplexing (SM) MIMO scheme is deployed in LTE and LTE-Advanced downlink to provide high data rates. In this communication, the authors will discuss a set of block decision detection techniques orientated to SM signals in MIMO-OFDM system. Both zero-forcing (ZF) and minimum mean square error (MMSE) schemes based detection versions are presented. Setting out from a novel general model for the evaluation of the signal-to-noise ratio (SNR) at the data detector output, the authors will evaluate the error ratio performance of the novel MIMO detectors and provide comparison results. It will be shown that the simple block decision detectors rather than interference cancellation based schemes provide an attractive coded performance at a lower realization complexity.

On the performance evaluation of an LTE SFBC system with Wiener channel estimation in frequency-selective channels

The uncoded performance of an Alamouti space-frequency block code operating in a frequency-selective channel is studied in the presence of channel estimation errors. The Alamouti Maximum Likelihood (ML) symbol detector with linear combining is considered at the receiver. Imperfect channel estimates are provided by a realistic as well as robust Wiener interpolator. A closed-form expression of the uncoded error probabilities of a space-frequency block code employing an Alamouti with linear combining is derived. Our analysis is conducted in the framework of a Long-Term Evolution air interface. The impact of channel estimation errors on the uncoded performance of the system is evaluated as a function of key system parameters, such as the anticipated power delay profile at the channel estimator, the actual, i.e. true, power delay profile, the pilot spacing and the Wiener filter length. The role of partial knowledge of the channel statistics is investigated as well. Finally, we derive a lower bound from our closed-form expression and calculate the bit error outage of the linear Alamouti combiner in presence of log-normal fading signal-to-noise ratio (SNR).

On the physical layer performance of the release 8 E-UTRA downlink

The 3GPP (Third Generation Partnership Project) LTE (Long Term Evolution) activity towards the evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access, which is known as E-UTRA, was started in November 2004 and recently culminated in the Release 8 of the 3GPP technical specifications, cf. e.g. the technical specifications 3GPP TS 36.101 and 3GPP TS 36.201. In the case of the physical layer, the performance evaluation of E-UTRA must be based on the 3GPP technical recommendation TR 25.814, published in October 2006. This manuscript illustrates the performance which can be expected in the downlink of UTRA LTE in various conditions.

On the Performance of an LTE SFBC System in Frequency-Selective Channels in the Presence of Channel Estimation Errors

The uncoded performance of an Alamouti space-frequency block code operating in a frequency-selective channel is studied in the presence of channel estimation errors. The Alamouti Maximum Likelihood (ML) symbol detector with linear combining is considered at the receiver. Imperfect channel estimates are provided by a realistic Wiener interpolator. The impact of channel estimation errors and correlation mismatch on the uncoded performance of the system is evaluated as a function of key system parameters, such as the anticipated power delay profile at the channel estimator, the actual, i.e. true, power delay profile, the pilot spacing and the Wiener filter length. The role of partial knowledge of the channel statistics is investigated as well.

Closed-loop schemes in UTRA LTE and LTE-advanced

The 3GPP (Third Generation Partnership Project) LTE (Long Term Evolution) activity towards the evolved UMTS (Universal Mobile Telecommunications System) Terrestrial Radio Access, which is known as E-UTRA, was started in November 2004 and recently culminated in the Release 8 of the 3GPP technical specifications, cf. e.g. the technical specifications 3GPP TS 36.101 and 3GPP TS 36.201. In the case of the physical layer, the performance evaluation of E-UTRA must be based on the 3GPP technical recommendation TR 25.814, published in October 2006. This manuscript illustrates the performance which can be expected in the downlink of UTRA LTE in various conditions.

Optimum and suboptimum 2D channel estimation for UTRA LTE and LTE-advanced

In this work a space-frequency block coding (SFBC) system is considered, which is compliant to the Long-Term-Evolution (LTE) specification. The uncoded bit error ratio (BER) of the linear Alamouti SFBC detector with BPSK modulation in the presence of 2-dimensional (2D) channel estimation is analyzed. The work in this paper comprises frequency-selective and Doppler fading. The quality of robust and optimum channel estimation is investigated by derivation of the Cramer-Rao Lower Bound (CRLB) for the complex-valued channel estimates. The BER performance of the LTE SFBC receiver is studied considering channel estimation with robust and optimum Wiener intepolation. The paper shows the effect of key system parameters on the SFBC performance, such as the anticipated power delay profile and Doppler spectrum at the channel estimator, the actual, i.e. true, power delay and Doppler spectrum, the pilot spacing and the Wiener filter length.