Vahid Meghdadi

Accurate radio coverage assessment methods investigation for 3G/4G networks

Sufficient wireless coverage is necessary to initiate communication with mobile terminals. Mobile network operators must guarantee good radio coverage. Telecommunication regulatory services (TRS) and technicians are assigned the duty of regularly verifying the conformity of the radio coverage at least once a year. However, it is not possible to collect data at every point in a given area. Therefore, TRS have defined a methodology called Random Drive Test Route (RDTR) to measure the provided radio coverage. The objective of this work is to investigate the weakness of the RDTRs that TRS are using. We used ATOLL for radio planning. The coverage prediction is adjusted to actual field measurements. We propose a novel methodology, called Special Drive Test Routes (SDTR) for assessing the radio coverage level of existing and future mobile network technologies. We defined for the SDTR a set of parameters such as minimum number of samples to be collected, the speed range and the route according to the network density in the considered area. We collected the radio coverage channel performances using TEMS Investigation 15.1 (a tool for 3G/4G). The performance results showed that a type of SDTR processes better than RDTR in a given area (open or with obstacles).

Joint channel estimation and data demodulation algorithms for fast time varying band-limited frequency selective Rayleigh fading channels : a comparison study

In this paper, a comparison study is proposed between two recent algorithms which both perform joint channel and data estimation. The first one is the well known psp : per survivor processing algorithm and the second is called adaptive bloc sequence estimation (bse). Compared to the existing literature, we add, for our comparison study, the case of trellis coded transmissions combined with interleaving and deinterleaving techniques which are now currently employed for digital communications.RésuméUne comparaison des performances de deuxméthodes récentes d’estimation de la réponse impulsion-nelle d’un canal de communication non stationnaire et de décodage des séquences numériques transmises est proposée. Deux méthodes sont principalement étudiées : la technique du traitement par survivant (psp) et la technique d’estimation adaptative des données par blocs (bse) dans le contexte de transmissions numériques codées (mct : modulations codées en treillis) utilisant les techniques d’entrelacement et de désentrelacement.

Space-Time-Block-Coded Transmissions for Downlink MC-CDMA Transmissions Over Frequency-Selective Fading Channels

Mitigation of multipath fading effects and suppression of multiuser interference (MUI) constitute major challenges in the design of the third generation wireless mobile systems. Space-time (ST) coding offers a attractive solution to cope with mutipath fading, but most existing ST coding schemes assume flat fading channels that may not be realistic for wide-band communications. Especially multiuser ST block-coded transmissions through multipath fading channels present unique challenge in suppressing not only MUI but also intersymbol/chip interference. In this paper, we design ST multiuser transceivers for MC-CDMA quasi-synchronous systems, capable to reliably transmit over frequency-selective multipath downlink channels. The proposed system is able to provide transmit diversity and to guarantee symbol recovery in multiuser environments, regardless of unknown multipath. Unlike existing approaches, the mobile does not need to know the channel of other users. In addition to decoding simplicity, computer simulations show the performance merits of the proposed transceiver.

Turbo Interference Mitigation in Layered Space-Time MIMO DS-CDMA Uplink with TTCM(Turbo Trellis Coded Modulation)

In this paper we propose the use of a turbo receiver for the uplink of a MIMO CDMA system employing layered space-time transmission. The proposed receiver consists of a low complexity layered space-time multi-user detector using minimum mean squared error (MMSE) filtering with a-priori information and a bank of MAP SISO decoders. Using the soft estimates from a bank of MAP decoders we obtain soft values of the interfering symbols. The SISO multiuser detector subtracts the vector of the interfering symbols from the incoming signal. The resulting vector is then filtered by an adaptive MMSE filter to reduce the residual MAI. This process iterates by exchanging extrinsic informations between the bank of MAP decoders and the SISO multiuser detector. Turbo Trellis Coded Modulation (TTCM) is used as Forward Error Correcting (FEC) code due to its high bandwidth efficiency. Our computer simulations show that the proposed structure outperforms a classical iterative receiver based on parallel interference cancellation (PIC) as well as a non-iterative MMSE receiver. Furthermore, in a multiuser context, the proposed receiver offers an error performance similar to that of single-user case at high SNR.

Turbo soft interference cancellation for coded asynchronous ds/cdma

In this paper we propose a Multiuser receiver architecture which removes the Multiple Access Interference (Mai) by means of a Soft Input Soft Output (siso) multiuser detector followed by a bank of channel decoders. The extrinsic information at the output of the channel decoders are used to estimate the values of the interfering bits and the SISO multiuser detector subtracts the vector of the interfering bits from the incoming signal. The resulting vector is then filtered by an adaptive mmse filter to help remove the residual mai. The paper examines the use of such a receiver in the context of a synchronous awgn channel and then we generalize to the case of asynchronous multipath fading channels.RésuméDans cet article nous étudions la structure d’un récepteur multiutilisateurs qui élimine le brouillage d’accès multiple à l’aide d’un détecteur multiutilisateurs à sorties pondérées suivi d’un bane de décodeurs de canal. L’information extrinsèque en sortie de chaque décodeur de canal est utilisée pour estimer la valeur des bits brouilleurs et le détecteur multiutilisateurs retranche le vecteur des bits brouilleurs au signal d’entrée. Unfiltrage adaptatif selon les moindres carres est alors appliqué pour éliminer le brouillage d’accès multiple rèsiduel. Nous examinons l’implantation de ce récepteur dans les contextes d’un système synchrone à bruit additif gaussien et d’un système asynchrone à trajets multiples.

Modélisation D’amplificateurs de Puissance À État Solide et Validation À L’aide d’un Simulateur Système

A new model is presented in order to simulate the non-linear behavior of solid state power amplifiers. This model is based on static, together with dynamic measurements. The model has been validated through the use of the COSSAP system simulator. A good agreement has been found between measured and calculated curves, such as noise power ratio (npr) and bit error rate (BER)curves.RésuméUn nouveau modèle est présenté pour simuler le comportement des non-linéarités des amplificateurs de puissance à état solide. Ce modèle est caractérisé non seulement par les mesures statiques mais aussi par les mesures dynamiques. Étant installé sur le simulateur système COSSAP, ce modèle a été validé par comparaison avec les courbes expérimentales : la courbe du rapport de puissance de bruit et la courbe du taux d’erreurs binaires (teb).