Cristian Pelizzoni

Optimal MIMO UWB-IR Transceiver for Nakagami-fading and Poisson-Arrivals

In this contribution, we develop a (novel) fam- ily of Multiple-Input Multiple-Output (MIMO) UWB Impulse-Radio (UWB-IR) transceivers for Orthogonal PPM- modulated (OPPM) coded transmissions over (baseband) multipath-faded MIMO channels. To by-pass expensive channel-estimation procedures, the MIMO channel path- gains are assumed to be fully unknown at the receiver. Thus, according to the UWB-IR statistical channel-models currently reported in the literature for both indoor/outdoor application scenarios, we develop and analyze three versions of the resulting noncoherent transceiver, that are optimal for Nakagami, Gaussian, and Log-normal distributed channel- gains, respectively. As dictated by the Saleh-Valenzuela (SV) UWB model, the resulting noncoherent Maximum- Likelihood (ML) Decoder explicitly accounts for the Poisson- distribution of the path-arrivals. Hence, after analytically evaluating the performance of the proposed noncoherent transceiver via suitable versions of the Union-Chernoff bound, we prove that the family of Space-Time OPPM (STOPPM) recently presented in the Literature is able to at- tain full-diversity in the considered multipath-affected appli- cation scenario. To corroborate the carried out performance analysis, we report several numerical results supporting both the medium/long coverage ranges attained by the proposed STOPPM-coded noncoherent transceiver, and its perfor- mance robustness against the degrading effects induced by Inter-Pulse-Interference (IPI), spatially-correlated multipath fading and mistiming.

On the information throughput and optimized power allocation for MIMO wireless systems with imperfect channel estimation

In this paper, we focus on the throughput analysis, outage evaluation and optimized power allocation for Multiple-Input Multiple-Output (MIMO) pilot-based wireless systems subject to short-term constraints on the radiated power and equipped with a feedback-path for communicating back to the transmitter the imperfect MIMO channel estimates available at the receiver. The case of the ergodic throughput for Gaussian distributed input signals is analyzed, and the conditions for the (asymptotical) achievement of the Shannon capacity are pointed out. The main contributions of this work may be so summarized. First, we develop closed-form analytical expressions for the computation of the ergodic information throughput conveyed by the considered MIMO system for the case of ideal feedback link. Second, we present an iterative algorithm for the optimized power allocation over the transmit antennas that explicitly accounts for the imperfect MIMO channel estimates available at the receiver. Third, after relaxing the assumption of ideal feedback link, we test the sensitivity of the proposed power allocation algorithm on errors possibly introduced by the feedback channel, and then, we numerically evaluate the resulting throughput loss. Finally, we develop closed-form upper and lower bounds on the outage probability that are asymptotically tight.

A simple multiantenna transceiver for ultra wide band based 4GWLANs

In the last years a lot of attention has been paid to multiantenna systems with space-time coding (STC) and to ultra wide band (UWB). In this paper we aim to propose a transceiver scheme in order to evaluate if these two technologies can be considered adequate candidates for next generation WLANs. Merging ultra wide band signals with multiple antenna schemes allows us to achieve very high bit rate and error probability matched to QoS requested by 4GWLANs at low SNR. This contribution presents a simple way to combine ultra wide band and multiple antenna schemes so to improve performance and coverage with respect to the conventional UWB approach in order to promote this approach application scenarios by considering a base band channel model and selective are considered.

Maximum-Rate Node Selection for Power-Limited Multiantenna Relay Backbones

Wireless mesh networks (WMNs) are envisioned for extending the coverage of WLANs by interconnecting the underlying access points (APs) via high-capacity wireless backbones. Since the ultimate goal of a WMN is to provide Internet connectivity to residential clients, WMN traffic is mainly routed over the backbone either toward the Internet gateways (IGWs) or from the IGWs to the APs. In principle, the transport capacity of a WMN can further be upgraded by equipping the underlying backbone routers with multiantenna (MA) radio modules. Motivated by the above consideration, in this paper, we focus on the optimized node selection (e.g., path-routing) over MA mesh backbones when the target is to maximize the end-to-end routed information rate subject to a constraint on the total power available for the relays. Under the assumption of Rayleigh-distributed block fading, we assume that point-to-point capacity-achieving space-time codes (STCs) are used for the single-hop link. At first, we tackle the routing problem when neither interference mitigation (IM) nor transmit beamforming (TB) is performed at the relay nodes, and then, we extend the analysis to the cases when IM and/or TB are also carried out. The effects of channel-state-information (CSI) possibly available at the relay nodes are also investigated. So doing, we are able to gain insight about the combined effect of spatial multiplexing and IM capabilities of the overall MA architecture on both end-to-end capacity and access medium performance of the considered WMN.

When does interference not reduce capacity in multi-antenna networks?

Multi-user interference induces performance loss in terms of BER and channel capacity when present in a communication system. Nevertheless multi-user interference can be suppressed via signal processing techniques so to improve performance. In fact, the presence of this interference reduce the channel capacity region A. Carleial et al., (1975). In this work the conditions allowing perfect interference cancellation are derived so to arrive at the same capacity region of an interference-free network.

Minimization of Download Times for Large Files over Wireless Channels

The emerging proxy-based wireless content delivery networks (CDNs) should to be designed to download huge-size files over fading-affected channels. However, from a radio resource management point of view, several basic problems still need to be solved for such wireless delivery systems to operate efficiently. Specifically, due to the fading nature of the downlink channel, a still open basic problem is how to design optimal energy-allocation (for example, scheduling) policies that minimize the requested download time when constraints on the total available energy and peak energy are simultaneously active. In this contribution, this problem is solved for application scenarios where the downlink channel is slotted and continuous-state, the carried out traffic is elastic, and the resulting conveyed throughput is measured by any desired increasing concave rate function. Specifically, the optimal energy-allocation policy minimizing the download time is computed in closed form, and its performance is compared against that of a basic on-off heuristic energy scheduler on some Rayleigh-faded multi-antenna delivery systems of practical interest. The carried out performance comparisons point out that the presented optimal policy typically may outperform the heuristic one up to two orders of magnitude, especially when the delivery system is strongly energy limited.

Multi-antenna noncoherent ML synchronization for UWB-IR faded channels

This contribution focuses on the maximum likelihood (ML) noncoherent synchronization of multi-antenna transceivers working in faded environments and employing ultra-wideband impulse radio (UWB-IR) transmit technology. In particular, the Cramer-Rao bound (CRB) is derived for the general case of multiple input multiple output (MIMO) UWB-IR systems and used to compare the ultimate performance of three basic transmit schemes, thereinafter referred to as single input multiple output (SIMO), MIMO equal signaling (MIMO-ES), and MIMO orthogonal signaling (MIMO-OS) ones. Thus, the noncoherent ML synchronizer is developed for the better performing transmit scheme (i.e., the SIMO one) and its performance is evaluated under both signal acquisition and tracking operating conditions. The performance gain in the synchronization of UWB-IR signals arising by the utilization of the multi-antenna technology is also evaluated.

Turbo-like synchronization for UWB-IR links

This contribution deals with the Turbo-like noncoherent data-aided (e.g., no blind) synchronization of Ultra-Wideband Impulse-Radio (UWB-IR) terminals operating over broadband channels affected by multipath fading with ¿a priori¿ unknown number of paths. The synchronizer we develop achieves the data-aided joint estimate of the number of paths and their arrival times without requiring any a priori knowledge of the amplitude (module and sign) of the channel-gains. The ultimate performance of the proposed synchronizer is evaluated by considering the number of pilots needed to estimate the channel delays and, more, the Bit Error Rate achievable on the basis of delays and amplitude estimation. The idea behind this approach is to use a turbo-like structure to improve performance so to allow a SNR gain even if channel models are considered in the presence of Inter Pulse Interference (IPI).

A new family of optimized orthogonal Space-Times codes for PPM-based MIMO systems with imperfect channel estimates

In this contribution, we develop a single Multiple-Input Multiple Output (MIMO) transceiver for Orthogonal PPM (OPPM) data transmitted over (baseband) faded MIMO channels with a priori unknown path-gains. The signaling-scheme we adopt allows to equip the Maximum-Likelihood receiver with reliable estimates of the (possibly time-varying) MIMO channel, without reducing the conveyed information throughput. Hence, after evaluating the performance of the proposed transceiver via a suitable version of the Union-Chernoff Bound, we introduce a novel family of unitary orthogonal Space-Times Block Codes (e.g., the Space-Time OPPM codes), that are able to attain both maximum diversity and coding gains. Afterwards, we present closed-form formulas for evaluating the SNR loss induced by mistiming effects possibly impairing the received signals. Lastly, we report several numerical results supporting both the medium/long coverage ranges attained by the proposed transceiver in outdoor applications and its performance robustness against correlated channel fading, mistiming effects and degradation induced by dense-multipath fading.

Performance analysis of impulse-radio UWB networks impaired by multiple access interference

In this contribution we analyze the effect of multi-user interference in terms of user collision probability and collision probability at all, by showing the impact that different system parameters have on the collision probability and the effect that this last presents on codeword error probability both in forward error correcting (FEC) and automatic repeat request (ARQ) schemes.