Narcis Cardona

On the way towards fourth-generation mobile: 3GPP LTE and LTE-advanced

Long-Term Evolution (LTE) is the new standard recently specified by the 3GPP on the way towards fourth-generation mobile. This paper presents the main technical features of this standard as well as its performance in terms of peak bit rate and average cell throughput, among others. LTE entails a big technological improvement as compared with the previous 3G standard. However, this paper also demonstrates that LTE performance does not fulfil the technical requirements established by ITU-R to classify one radio access technology as a member of the IMT-Advanced family of standards. Thus, this paper describes the procedure followed by the 3GPP to address these challenging requirements. Through the design and optimization of new radio access techniques and a further evolution of the system, the 3GPP is laying down the foundations of the future LTE-Advanced standard, the 3GPP candidate for 4G. This paper offers a brief insight into these technological trends.

Application Layer FEC for Mobile TV Delivery in IP Datacast Over DVB-H Systems

In this paper we investigate the potential gain that can be obtained in DVB-H using application layer forward error correction (AL-FEC) to perform a multi-burst protection of the transmission for improving the reception of streaming services for mobile terminals. Compared to the conventional approach with link layer multi protocol encapsulation FEC (MPE-FEC), this technique allows to increase the robustness of the DVB-H transmission not only as a function of the capacity devoted for error repair (FEC overhead), but also as a function of the number of bursts jointly encoded. The main drawback of this approach is an increase of the network latency, that can be translated into a larger service access time, and, in the case of mobile TV, a larger zapping time between channels, which is currently seen as a crucial parameter for DVB-H usability. In this paper the performance of the proposed approach is evaluated using field measurements. We evaluate the gain compared to MPE-FEC in terms of reduced IP packet error rate of the streaming service as a function of the FEC overhead and the latency introduced. Moreover, simulations have been performed to quantify feasible link margin gains. We also discuss techniques to reduce and hide the zapping time from the perception of the users.

Affordable Mobile TV Services in Hybrid Cellular and DVB-H Systems

Mobile TV services are expected to become a key application in future wireless networks. The recently proposed terrestrial digital broadcast technology, DVB-H, especially designed for mobile services, is regarded as a powerful alternative to the 3G cellular networks that already offer these services out on a point-to-point basis. Unfortunately, the cost of supporting real-time streaming and full area coverage seems to be very high compared to fixed TV services. In this article we discuss hybrid IP datacast DVB-H and 3G systems as a possible solution for providing affordable network infrastructure and services. Our approach is DVB-H centric. The 3G cellular system plays the role of providing interactivity, error reporting, and repair for the DVB-H broadcast channel. To enable an easy and efficient interworking of DVB-H and 3G, we employ forward error correction at the application layer with digital fountain coding. The main way to provide lower cost services is to avoid full DVB-H area coverage from the beginning and to perform an incremental DVB-H network deployment that follows the user demand. In this direction, to hide the discontinuity in coverage from the perception of users, we propose to take advantage of the bursty character of DVB-H transmissions and the mobility of users. This is possible by sending additional parity data, either with the DVB-H or the cellular network, in the time intervals between original service bursts. We evaluate the potential DVB-H infrastructure cost savings determined by transmitting additional parity data in DVB-H when targeting vehicular users. The implications of delivering parity data through the cellular network also are discussed. The numerical investigations show a potential for significant cost savings compared with the traditional approaches

Multicast Delivery of File Download Services in Evolved 3G Mobile Networks With HSDPA and MBMS

This article presents and analyzes the multicast transmission problem of file download services to several users simultaneously in 3G mobile networks with MBMS (multimedia broadcast multicast services). MBMS is the second major enhancement in the downlink of the 3G standard after HSDPA (high-speed downlink packet access). Whereas HSDPA supports high speed point-to-point (p-t-p) transmissions up to several Mb/s, with MBMS the same content can be transmitted with a point-to-multipoint (p-t-m) connection to multiple users in a unidirectional fashion. Reliable delivery of files is a challenging task, as an error-free reception of the files is required. In order to increase the robustness of the p-t-m transmission, MBMS adopts new diversity techniques to cope against fast fading and to combine transmissions from multiple cells, and an additional forward error correction (FEC) mechanism at the application layer based on Raptor coding. Moreover, users not able to receive the file after the initial transmission can complete the download in a post-delivery repair phase, in which it is possible to employ both p-t-p and p-t-m connections. The article focuses on the efficient multicast delivery of files in future 3G mobile networks with HSDPA and MBMS. Delivery configurations studied include: only p-t-p transmissions with HSDPA (one for each active user), a single p-t-m transmission with MBMS, and using both jointly in a hybrid approach employing HSDPA for error repair of the MBMS transmission. The approach of minimizing the transmission energy (product of the transmit power times the transmission time) to achieve a target file acquisition probability (percentage of users that successfully receive the file) has been adopted. Radio network simulations have been performed in a typical urban scenario under full background load conditions. This way by minimizing the energy the system capacity is maximized. We investigate the optimum HSDPA and MBMS transmission configurations as a function of the time to deliver the file when used separately, and the optimum trade-off between the initial MBMS file transmission and the HSDPA error repair for the hybrid delivery.

MIMO for DVB-NGH, the next generation mobile TV broadcasting [Accepted From Open Call]

DVB-NGH (Digital Video Broadcasting - Next Generation Handheld) is the next generation technology for mobile TV broadcasting, which has been developed by the DVB project with the most advanced transmission technologies. DVB-NGH is the first broadcasting standard to incorporate multiple-input multiple-output (MIMO) as the key technology to overcome the Shannon limit of single antenna communications. MIMO techniques can be used to improve the robustness of the transmitted signal by exploiting the spatial diversity of the MIMO channel, but also to achieve increased data rates through spatial multiplexing. This article describes the benefits of MIMO that motivated its incorporation in DVB-NGH, reviews the MIMO schemes adopted, and discusses some aspects related to the deployment of MIMO networks in DVB-NGH. The article also provides a feature comparison with the multi-antenna techniques for 3GGPs LTE/LTE-Advanced for cellular networks. Finally, physical layer simulation results calibrated within the DVB-NGH standardization process are provided to illustrate the gain of MIMO for the next generation of mobile TV broadcasting.

Time Diversity in Mobile DVB-T2 Systems

DVB-T2 implements a very flexible time interleaving that allows multiple tradeoffs in terms of time diversity, latency and power saving. In this paper, we study in detail these tradeoffs in the context of mobile reception. Together with time diversity, we also investigate the impact of reduced time de-interleaving memory and Alamouti-based MISO in the mobile reception of DVB-T2 services. In addition, we propose the utilization of upper layer FEC protection in order to overcome the limitations of the DVB-T2 physical layer for the provision of long time interleaving, and enable fast zapping. The performance is evaluated by means of simulations in mobile channels that include the presence of fast fading and shadowing in the received signal.

Mobile radio bi-dimensional large-scale fading modelling with site-to-site cross-correlation

Wireless communication simulations are generally conducted using one-dimensional models for large-scale fading. While simple and with low computational costs, these models cannot produce correlated fading values for mobiles that are in nearby positions. To overcome this limitation, this paper presents a novel bi-dimensional large-scale fading model which introduces the spatial correlation present in real systems. Besides, it is also able to model the non-negligible cross-correlation among signals coming from different sites. Copyright

Coexistence of digital terrestrial television and next generation cellular networks in the 700 MHz band

With the spectrum liberation obtained by the deployment of digital terrestrial television and the analog TV switch-off, new bands are being assigned to IMT LTE. In the first cellular deployments in the digital dividend at the 800 MHz band, problems emerged due to the interference cellular networks can cause to DTT signals. Possible solutions imply either an inefficient use of the spectrum (increasing the guard band and reducing the number of DTT channels) or a high cost (using anti-LTE filters for DTT receivers). The new spectrum allocated to mobile communications is the 700 MHz band, also known as the second digital dividend. In this new IMT band, the LTE uplink is placed in the lower part of the band. Hence, the ITU-R invited several studies to be performed and reported the results to WRC-15. In this article, we analyze the coexistence problem in the 700 MHz band and evaluate the interference of LTE signals to DTT services. Several coexistence scenarios have been considered, and laboratory tests have been performed to measure interference protection ratios.

Random access channel (RACH) parameters optimization in WCDMA systems

The random access procedure, defined by the 3rd Generation Partnership Project (3GPP), is based on a slotted Aloha approach with fast acquisition indication, that is carried out in uplink by the random access channel (RACH) and acquisition indicator channel (AICH) in the downlink. In this paper, the RACH performance in a single omni cell under shadowing and fast-fading conditions is analyzed. An optimization procedure is performed to obtain, according to random access delay and random access success ratio, optimal values for RACH radio parameters such as the power offset between consecutive preambles (/spl Delta//sub pp/) and the preamble target signal to interference ratio (SIR/sub t/). Furthermore, curves of preamble signal to interference ratio (SIR), measured at base station point, are presented.

Minimal Cost Planning of DVB-H Networks on Existing Wireless Infrastructure

This paper addresses the problem of efficient planning DVB-H networks assuming that the existing broadcasting and cellular infrastructure can be used in the network deployment. The planning objective consists in deciding which existing cellular sites should be used jointly with the broadcasting towers in a minimum cost deployment. A multi-objective genetic algorithm has been utilized to seek minimum cost network configurations as a function of the area coverage level. We investigate the achievable cost savings offered by a hybrid infrastructure compared to using only the existing broadcasting towers and the cellular sites separately