Stephanie Rouquette-Leveil

Transmit diversity and spatial multiplexing in four-transmit-antenna OFDM

This paper studies a practical design for achieving both spatial diversity and spatial multiplexing in an OFDM system with four transmit antennas. In a certain range of spectral efficiency, the proposed hybrid space-time block coding/multiple-input multiple-output (STBC/MIMO) design is found to be a good design choice based on performance and receiver complexity, when compared with MIMO-only or diversity-only STBC designs. For the hybrid design, we propose a simple receive algorithm that requires no matrix inversion. Outage capacity evaluated with a Monte Carlo approach is used to provide insight into the simulation-based comparison of the different designs. The robustness to channels that lack spatial separability is also studied in the simulations.

Error prediction for adaptive modulation and coding in multiple-antenna OFDM systems

In this paper, the problem of packet error rate (PER) prediction is addressed in the multiple-antenna broadband OFDM context, and its impact on adaptive modulation and coding (AMC) is quantified. The analysis is based on a physical layer comprising various modulation and coding schemes, ranging from robust space-time block coding (STBC) modes to high bit rate spatial division multiplexing (SDM) modes, and also hybrid SDM-STBC schemes. For each mode the expression of several link quality metrics (LQM) enabling PER prediction in the broadband OFDM channel, such as instantaneous signal-to-noise ratio (SNR), capacity, or exponential effective SNR metrics are provided. Their advantages and limitations are investigated. Finally, their performance is benchmarked in the IEEE 802.11a/g/n context. It is shown that the choice of the LQM has a significant impact on the throughput performance of the AMC algorithm.

On the performance of the Golden code in BICM-MIMO and in IEEE 802.11n cases

In 2times2 MIMO systems, the Golden code (GC) [1] was proposed when no binary outer code is applied at the transmitter. This code is optimal since it achieves full rate, full diversity and the Diversity Multiplexing Tradeoff [2], and it preserves the mutual information. We propose in this paper to study the performance of this code compared to Spatial Division Multiplexing (SDM) [3] in a BICM-MIMO system. We derive the Pairwise Error Probability (PER) in this context and we assess our results over a Rayleigh channel and in the 802.11n case. We show that the GC is also optimal for 2 times 2 BICM-MIMO systems. However, the impact of the additional gain provided by the Golden code is reduced when using binary outer code with high free distance case, as for instance in IEEE 802.11n standard.

Space-time coding options for OFDM-based WLANs

Space-time block codes and space-time trellis codes have recently been introduced to improve the performance of wireless systems. In this paper, we reconsider first the design criteria for space-time trellis codes in our context of application that is OFDM-based WLAN. We show by simulations that the rapid Rayleigh fast fading criteria are appropriate and we propose a code optimized accordingly. Then, we compare space-time block coding solutions with trellis-based ones, both including convolutional coding and interleaving. For that purpose, we also designed and simulated a rate 1/2 space-time trellis code, in which the channel and space-time coding are jointly optimized.

DMT achieving schemes for the isotropic fading vector broadcast channel

In this paper, we consider the isotropic fading broadcast channel. This channel refers to the case when no directional information is available at the transmitter side, and was studied by Jafar et al in. It was shown that the isotropic vector broadcast channel (BC-V) can be reduced to an equivalent scalar broadcast channel (BC-S). It is well known from [2]http://www.pimrc2008.org/ that BC-S is degraded in the same order as the channel magnitude. This implies that the optimal strategy that maximizes the sum capacity for BC-S and BCV consists on allocating the whole power to the strongest user. Based on these results, we derive in this paper the diversity multiplexing tradeoff (DMT) of the isotropic fading BC-S and BC-V, and we propose optimal schemes that achieve these DMT.

Application of Perfect Space Time Codes: PEP Bounds and Some Practical Insights

The design of perfect space time codes constructed from cyclic division algebra (CDA) on the quasi-static MIMO channel has received lots of attention in industry over the last few years. However, the recent standards that use multiple antennas terminals such as IEEE 802.11n, IEEE 802.16e or LTE are based on more realistic assumptions involving the use of outer codes and multi-taps channels. In this paper, the question regarding the utility of using a high dimensional modulation schemes such as space time codes in a standard context is addressed. For this, we evaluate the performance of the perfect space time codes in term of an upper-bound on the pairwise error probability, and we compare it to the one of simple spatial division multiplexing (SDM) schemes. Finally, simulation results considered in the context of IEEE 802.11n show that the 2 × 2 MIMO perfect code, i.e. the golden code performs relatively similarly as the SDM scheme in the presence of a good outer code.

Impact of realistic receiver RFFE model on macro-diversity versus micro-diversity system capacity

This paper studies the evolution of Multiple-Input Multiple-Output (MIMO) system capacity in the context of macro-diversity antenna configurations, with respect to system parameters such as the distance between mobile devices. In this context, we redefine an accurate channel model by proposing a realistic configuration of the RF front-end (RFFE). The impact of this improved model on system capacity is first checked in the micro-diversity context, when comparing our results with the model classically used in the literature. This new model is shown to explain some phenomena observed in actual implementations. Then, in the macro-diversity context, we concentrate on the usefulness of adding antennas, depending on the distance to the transmitter or receiver. The obtained results are strongly impacted by the RFFE model

DMT of weighted parallel channels: Application to broadcast channels

In a broadcast channel with random packet arrival and transmission queues, the stability of the system is achieved by maximizing a weighted sum rate capacity with suitable weights that depend on the queue size. The weighted sum rate capacity using Dirty Paper Coding (DPC) and Zero Forcing (ZF) is asymptotically equivalent to the weighted sum capacity over parallel single-channels. In this paper, we study the Diversity Multiplexing Tradeoff (DMT) of the fading broadcast channel under a fixed weighted sum rate capacity constraint. The DMT of both identical and different parallel weighted MISO channels is first derived. Finally, we deduce the DMT of a broadcast channel using DPC and ZF precoders.

Reconfigurable Low Density Parity Check (LDPC) Code Interleaving for SIO and MIMO OFDM Systems

This contribution derives an algorithm for optimizing the mapping of irregular and systematic low density parity check (LDPC) code word bits onto orthogonal frequency division multiplexing (OFDM) carriers in the context of a frequency selective fading channel in both, a single-transmit single-receive (SISO channel) and multiple-transmit multiple-receive (MIMO channel) antennas scenario. The absolute values of the frequency domain channel coefficients are assumed to be known and the LDPC code to be given (contrary to existing proposals where the LDPC code is optimized with respect to a given propagation channel). The proposed solution can alternatively be interpreted as an adaptive interleaver (which is inherently available in software defined radio type of system implementations) optimized for a given channel impulse response. In a typical WLAN (IEEE802.11n) scenario, the proposed mapping technique improves the system performance by up to approx. 0.7 dB compared to a linear (direct) mapping

Macro-diversity versus micro-diversity system capacity with realistic receiver RFFE model

This paper studies the evolution of multiple-input multiple-output (MIMO) system capacity in the context of macro-diversity antenna configurations, with respect to system parameters such as the distance between mobile devices. In this context, we redefine an accurate channel model by proposing a realistic configuration of the RF front end (RFFE). The impact of this improved model on system capacity is first checked in the micro-diversity context, when comparing our results with the model classically used in the literature. This new model is shown to explain some phenomena observed in actual implementations. Then, in the macro-diversity context, we concentrate on the usefulness of adding antennas, depending on the distance to the transmitter or receiver. The obtained results are strongly impacted by the RFFE model.