Christian Sgraja

Cellular In-Band Modem Solution for eCall Emergency Data Transmission

eCall is a project of the European Commission for the improvement of transportation safety by providing rapid assistance to motorists involved in a collision anywhere in the European Union. In the event of a collision, the intended solution employs an in-band modem that transmits vehicle location, airbag deployment, and other relevant information timely and reliably from the in-vehicle system (IVS) over the cellular network voice channel to the public safety answering point (PSAP). This paper describes the requirements, system design and performance of the eCall in-band modem solution that was selected by 3GPP. Due to the employment of this solution in life-critical situations, transmission reliability and speed are of utmost importance. The effective transmission channel is characterized by the highly nonlinear speech codec, as well as radio channel impairments, constituting a challenge for the in-band transmission of digital data. Several innovative transmission concepts were developed for our eCall in-band modem solution to address this challenge.

Performance Evaluation of Multicast/Broadcast Single Frequency Network Operation for WCDMA

Multimedia broadcast/multicast services (MBMS) have been introduced for WCDMA in release 6. At a given coverage, the efficiency of conventional MBMS is limited by low SNR users as, e.g., users located close to a cell edge, which are typically suffering from bad channel and inter-cell interference conditions. As a means to mitigate the situations of such users, multicast/broadcast single frequency network (MBSFN) operation has recently been specified in the Third Generation Partnership Project (3GPP) as an enhancement of MBMS. In WCDMA downlinks as considered here, MBSFN operation refers to the coherent use of a single common scrambling code and the same spreading codes to simultaneously broadcast identical MBMS channels in a number of cells that form an MBMS cluster. Through this, the users receive the signals from the cluster of MBSFN cells as one single signal over a joint radio channel, which exchanges inter-cell interference by constructive multi-path signals. This can be exploited by advanced receivers to yield impressive receiver output SNR gains as compared to conventional MBMS. This paper presents an experimental evaluation of the spectral efficiencies achievable in MBSFN and conventional MBMS. The results help to assess whether it is expedient to enhance WCDMA by MBSFN.

Iterative soft Cholesky block decision feedback equalizer-a promising approach to combat interference

A novel iterative soft block decision feedback scheme, capable to cope with general complex valued modulation symbols and to combat both inter-symbol and inter-user interference, is introduced. It is shown that this new scheme has the capability to achieve optimum maximum likelihood performance and does not suffer from the unavoidable loss of received power in a classical DFE scheme. As an example we apply the introduced detection algorithm to the K-symmetric multiuser channel and compare the results to both the classical block decision feedback equalizer and to maximum likelihood equalization.

On the Impact of Coarse Synchronization on the Performance of Broadcast/Multicast Single Frequency Network Operation in WCDMA

We evaluate the system-level performance and potential capacity gain of MBSFN (Multicast/Broadcast Single Frequency Network) operation in wideband CDMA (WCDMA) and compare it to conventional multimedia broadcast/multicast service (MBMS) provision with macro-diversity combining. MBSFN operation has recently been specified in the 3rd Generation Partnership Project (3GPP) as an enhancement to MBMS. It aims to mitigate the cell-edge problem of multicast/broadcast applications, which are typically dimensioned for a predefined coverage. In WCDMA as considered here, MBSFN operation refers to the use of a single common scrambling code and the same set of spreading codes to simultaneously broadcast bit identical MBMS data in a number of cells that form an MBMS cluster. Since intercell interference is drastically reduced by this concept, it has the potential of considerably increasing the spectral efficiency of MBMS. Nevertheless, coarse synchronization of the transmitting base stations is expected to degrade the performance of MBSFN. We study the system-level performance of MBSFN for WCDMA with imperfect synchronization of the base stations considering different equalization strategies.

On Discrete-Time Modeling of Time-Varying WSSUS Fading Channels

The general property of noncommutativity of linear time-varying (LTV) systems has to be considered when a digital transmission system composed of LTV channel and transmit/receive filtering shall be represented in the equivalent discrete-time domain. In this correspondence, we analyze the implications of serially concatenated LTV systems with respect to the discrete-time representation of wide-sense stationary uncorrelated scattering (WSSUS) fading channels. We provide a detailed discussion of the largest tolerable channel Doppler spread (in relation to the system bandwidth) for which the concatenation is commutative in good approximation. In this case, the discrete-time description facilitates an efficient simulation model. The approximation accuracy is quantified by a detailed error analysis and further verified by numerical simulation adopting Universal Mobile Telecommunications System (UMTS) parameters.