João Carlos Silva

Usage of link-level performance indicators for HSDPA network-level simulations in E-UMTS

The paper describes integration of HSDPA (high-speed downlink packet access) link-level simulation results into network-level simulations for enhanced UMTS. The link-level simulations model all physical layer features depicted in the 3GPP standards. These include: generation of transport blocks; turbo coding; rate matching; spreading; scrambling; modulation. At the receiver side, all complementary blocks are designed, with soft-decision demodulation, and a turbo decoder using the MAP (maximum a posteriori) algorithm with 8 iterations. An analytical formula is defined that fits the CQI (channel quality indicator) dependent BLER (block error rate) versus E/sub b//N/sub 0/ results in an AWGN channel. This formula models the physical layer in the network-level simulator. A further extension for frequency selective fading channels has been defined. The network-level simulator includes propagation models that provide SNR values. Based on these SNR values and the simplified physical layer model, an algorithm selects the CQI, and determines the actual BLER at time of reception. The rounding down and delaying of the CQI reporting, which corresponds to the W-CDMA standard, has a significant impact on throughput and transfer delay of the HS-DSCH. Some compensation can be found in a modified transmission. The integration of the link-level and network-level simulators gives accurate and realistic results that can be used in more studies that focus on network layer aspects of packet based services over HSDPA.

Multi-Resolution Broadcast/Multicast Systems for MBMS

Multimedia Broadcast/Multicast Service (MBMS) supports downlink streaming and download-and-play type services to large groups of users. From the radio perspective, MBMS includes point-to-point (PtP) and point-to-multipoint (PtM) modes. This paper investigates and presents different multi-resolution broadcast systems for Wideband Code Division Multiple Access (WCDMA) cellular mobile networks, namely, multi-code, hierarchical QAM constellations and multi-antenna (MIMO) systems. Each one present performance gains over conventional single-resolution broadcast systems. A comparison is made between the three proposed multi-resolution systems. The use of High Speed Downlink Packet Access (HSDPA) to multicast video streaming as a multi-resolution system, associated or not to MIMO, can be employed by the MBMS PtP mode, but dependently on the deployment scenarios it can yield substantial reduction in resource demand and optimization of the allocated radio resources

On the BER Performance of Hierarchical

The analytical bit error rate of hierarchical quadrature amplitude modulation formats, which include uniform and nonuniform constellations, over flat Rayleigh fading environments is studied in this paper. The analysis takes into account the effect of imperfect channel estimation and considers diversity reception with both independent identically and nonidentically distributed channels, employing maximal ratio combining.

M

Multimedia broadcast and multicast services (MBMS) specified in 3GPP Release 6 are expected to be transmitted to large groups of users within the cell range. MBMS counting mechanism intends to analyse whether it is more economic to transmit the multimedia services in a point-to-point (PtP) or point-to-multipoint (PtM) mode, evaluating in terms of radio resources management whether it is preferable to use a single common channel reaching down the cell edge or single dedicated channels allocated to each user which convey identical MBMS content. MBMS counting mechanism was initially developed without consideration of macro diversity combining (MDC) and users were only counted in each cell individually which can result in a waste of radio resources. With the introduction of MDC techniques users need to be counted in several cells so that they can successfully receive the MBMS services at the cell edge

-QAM Constellations With Diversity and Imperfect Channel Estimation

In the Long Term Evolution (LTE) of UMTS the Interactive Mobile TV scenario is expected to be a popular service. By using multiresolution with hierarchical modulations this service is expected to be broadcasted to larger groups achieving significant reduction in power transmission or increasing the average throughput. Interactivity in the uplink direction will not be affected by multiresolution in the downlink channels, since it will be supported by dedicated uplink channels. The presence of interactivity will allow for a certain amount of link quality feedback for groups or individuals. As a result, an optimization of the achieved throughput will be possible. In this paper system level simulations of multi-cellular networks considering broadcast/multicast transmissions using the OFDM/OFDMA based LTE technology are presented to evaluate the capacity, in terms of number of TV channels with given bit rates or total spectral efficiency and coverage. multiresolution with hierarchical modulations is presented to evaluate the achievable throughput gain compared to single resolution systems of Multimedia Broadcast/Multicast Service (MBMS) standardised in Release 6.

UE Counting Mechanism for MBMS Considering PtM Macro Diversity Combining Support in UMTS Networks

Single carrier transmissions with frequency domain equalization (SC-FDE) have gained widespread use in emergent broadband wireless systems becoming an attractive alternative to popular Orthogonal Frequency Division Multiplexing (OFDM) schemes, particularly at the uplink. Since coherent receivers are usually employed with SC-FDE, accurate channel estimates are required so as to avoid substantial performance degradation. Several channel estimation strategies have been proposed for SC-FDE, but a thoroughly evaluation of the degradation caused by channel estimation errors and a comparison against OFDM is still lacking. In this paper we study the impact of imperfect channel knowledge on SC transmission with focus on the linear frequency domain equalizer (FDE) and on the Iterative Block Decision Feedback Equalizer (IB-DFE). We propose a modified IB-DFE which incorporates knowledge of the channel estimation error model and show that its performance becomes more robust against the presence of strong error components in the channel estimates. We also evaluate, analytically and through simulations, the degradation caused by imperfect channel estimation in SC-FDE and compare it against OFDM schemes (Orthogonal Frequency Division Multiplexing). It is shown that the channel estimation requirements for SC-FDE are higher than for OFDM unless a channel estimation error aware receiver is employed.

Multiresolution with hierarchical modulations for long term evolution of UMTS

In this paper we consider the use of M-QAM hierachical constellations (quadrature amplitude modulation) and MIMO (multiple input multiple output) for the transmission of multicast and broadcast services in the downlink connection of a WCDMA (wideband code division multiple access) system. The objective is to increase the efficiency of the transmission by splitting the information in classes with different importance and mapping the bit streams of these classes to more or less protected positions of the modulation symbols. With this strategy, the most important information streams can be received by all users while the less relevant information will only be extracted by users with good propagation conditions. Due to the more demanding channel estimation requirements and the higher sensitivity to interference resulting from the usage of several antennas and hierarchical constellations, an enhanced receiver based on the turbo concept is developed and evaluated. It is shown that high transmission bit rates can be achieved even in high delay spread environments

Impact of Channel Estimation Errors on SC-FDE Systems

In this paper we consider the use of non-uniform QAM constellations (quadrature amplitude modulation) for the transmission of multicast and broadcast services in the downlink connection of a WCDMA (wideband code division multiplexing) system. The objective is to increase the efficiency of the transmission by splitting the information in classes with different importance and mapping the bit streams of these classes to more or less protected positions of the modulation symbols. With this strategy, the most important information streams can be received by all users while the less relevant information will only be extracted by users with good propagation conditions. It is shown that the multipath interference introduced by the channel induces a severe performance loss for these modulations. A low complexity iterative turbo multipath interference canceller (MPIC) that uses feedback information from the turbo-decoder is proposed for suppressing this interference. Computer simulation results are presented, showing that a considerable performance gain can be obtained with the use of the iterative MPIC.

An Iterative Receiver for WCDMA Systems with MIMO Transmissions and Hierarchical Constellations

Among radio technologies, multiple-input multiple-output (MIMO) systems have attracted wide research interests in recent years. It is widely recognized that MIMO systems can be employed for achieving a high capacity and a high diversity order, for mitigating the effects of various types of interfering signals, and for supporting space-division multiple-access (SDMA). In this study a MIMO assisted cellular system using distributed antennas is proposed and investigated, where a big number of antennas are distributed in the area covered by the system. The proposed system is capable of providing a platform for possibly integrating the conventional cellular systems into the future advanced, high-flexibility, ad-hoc and cooperative wireless networks. This system is considered for MBMS (multimedia broadcast multicast service) that enables mobile operators to deliver rich multimedia to a huge number of subscribers by broadcasting over the radio frequencies assigned to WCDMA.

Iterative turbo multipath interference cancellation for WCDMA systems with non-uniform modulations

When simulating reference tapped delay line channel models, there is usually the problem of matching all the replica delays with simulation sampling instants. To avoid a substantial increase in simulation time, several conversion methods for obtaining channel models, with all replica delays matching sampling instants, are studied. Simulation results of a WCDMA system using RAKE receivers are shown for verifying the closeness of the results of the channel models.