Power Efficient SDR Implementation of IEEE 802.11a/p Physical Layer

Software defined physical layer modems can be considered the new trend in the field of communications. Differently from dedicated hardware, software can be easily modified to implement a large variety of standards on the same platform. The use of software can significantly reduce development costs, but generally comes at the price of an increase in silicon area and power consumption. For different reasons, this price is something that is not always convenient or even possible to pay, as in the case of low-cost ICs implementing a single waveform, or even multi-mode modems embedding legacy IPs already available in hardware. In particular, power consumption overhead can be prohibitive for mobile terminals or in general for battery-powered devices. The very first challenge for a computing fabric to be competitive is to find and implement the right trade-off between flexibility and performance. This was the guideline for the design of the Block Processing Engine (BPE), a template architecture conceived for power-efficient baseband processing. The BPE core feature is a mixed-grain instruction set balancing general-purpose fine-grain instructions with more specific coarse-grain instructions wrapping custom hardware modules. To further limit the power consumption, the BPE also implements instruction-pipelining, variable-size SIMD and multi-task support. To prove the efficiency of such an approach, a dual-mode IEEE 802.11a/p receiver has been implemented.     

Susceptible Workload Evaluation and Protection using Selective Fault Tolerance

Low power fault tolerance design techniques trade reliability to reduce the area cost and the power overhead of integrated circuits by protecting only a subset of their workload or their most vulnerable parts. However, in the presence of faults not all workloads are equally susceptible to errors. In this paper, we present a low power fault tolerance design technique that selects and protects the most susceptible workload. We propose to rank the workload susceptibility as the likelihood of any error to bypass the logic masking of the circuit and propagate to its outputs. The susceptible workload is protected by a partial Triple Modular Redundancy (TMR) scheme. We evaluate the proposed technique on timing-independent and timing-dependent errors induced by permanent and transient faults. In comparison with unranked selective fault tolerance approach, we demonstrate a) a similar error coverage with a 39.7% average reduction of the area overhead or b) a 86.9% average error coverage improvement for a similar area overhead. For the same area overhead case, we observe an error coverage improvement of 53.1% and 53.5% against permanent stuck-at and transition faults, respectively, and an average error coverage improvement of 151.8% and 89.0% against timing-dependent and timing-independent transient faults, respectively. Compared to TMR, the proposed technique achieves an area and power overhead reduction of 145.8% to 182.0%.     

Space–Time Coding for Multiuser Ultra-Wideband Communications

In this paper, we present the construction of full rate, fully diverse, and totally real space-time (ST) codes for ultra-wideband (UWB) transmissions. In particular, we construct two families of codes adapted to real carrierless UWB communications that employ pulse position modulation, pulse amplitude modulation, or a combination of the two. The first family encodes adjacent symbols and is constructed from totally real cyclic division algebras. The second family encodes the pulses used to convey one information symbol, and permits achieving high performance levels with reduced complexity. The first family of codes achieves only a fraction of the coding gain of the second one. Moreover, these coding gains are independent from the size of the transmitted constellation. For time-hopping multiple-access channels, the amplitude spreading code associated with the second family of codes is taken to be user-specific. In this case, a simple design criterion is proposed, and spreading matrices constructed according to this criterion permit reducing the level of multiple-access interference (MAI). Simulations performed over realistic indoor UWB channels verify the theoretical claims and show high performance levels and better immunity against MAI     

Ionic‐Liquid Gating of InAs Nanowire‐Based Field‐Effect Transistors

Here, the operation of a field‐effect transistor based on a single InAs nanowire gated by an ionic liquid is reported. Liquid gating yields very efficient carrier modulation with a transconductance value 30 times larger than standard back gating with the SiO₂/Si₊₊ substrate. Thanks to this wide modulation, the controlled evolution from semiconductor to metallic‐like behavior in the nanowire is shown. This work provides the first systematic study of ionic‐liquid gating in electronic devices based on individual III–V semiconductor nanowires: this architecture opens the way to a wide range of fundamental and applied studies from the phase transitions to bioelectronics.     

Hierarchically Structured Magnetic Nanoconstructs with Enhanced Relaxivity and Cooperative Tumor Accumulation

Iron oxide nanoparticles are formidable multifunctional systems capable of contrast enhancement in magnetic resonance imaging, guidance under remote fields, heat generation, and biodegradation. Yet, this potential is underutilized in that each function manifests at different nanoparticle sizes. Here, sub‐micrometer discoidal magnetic nanoconstructs are realized by confining 5 nm ultra‐small super‐paramagnetic iron oxide nanoparticles (USPIOs) within two different mesoporous structures, made out of silicon and polymers. These nanoconstructs exhibit transversal relaxivities up to ≈10 times (r ₂ ≈ 835 mm ^?1 s^?1) higher than conventional USPIOs and, under external magnetic fields, collectively cooperate to amplify tumor accumulation. The boost in r ₂ relaxivity arises from the formation of mesoscopic USPIO clusters within the porous matrix, inducing a local reduction in water molecule mobility as demonstrated via molecular dynamics simulations. The cooperative accumulation under static magnetic field derives from the large amount of iron that can be loaded per nanoconstuct (up to ≈65 fg) and the consequential generation of significant inter‐particle magnetic dipole interactions. In tumor bearing mice, the silicon‐based nanoconstructs provide MRI contrast enhancement at much smaller doses of iron (≈0.5 mg of Fe kg^?1 animal) as compared to current practice.     

On the Amplify-and-Forward Cooperative Diversity with Time-Hopping Ultra-Wideband Communications

In this paper, we extend the Amplify-and-Forward cooperative diversity scheme to the context of impulse radio ultra wideband (IR-UWB). In particular, we present the construction of three families of minimal-delay and totally-real distributed algebraic space-time (ST) codes suitable for IR-UWB. The first family encodes adjacent symbols and is based on totally-real cyclic division algebras. The second family encodes the pulses used to transmit one information symbol and permits to achieve high performance levels with lower complexity. Both families of codes achieve full rate, full diversity with non-vanishing determinants for various number of relays. These schemes can be associated with pulse position modulation (PPM), pulse amplitude modulation (PAM) and hybrid pulse position and amplitude modulation (PPM-PAM). The third family of codes is information-lossless and does not require any pulse repetitions. It is specific to M-PPM-M'-PAM with M ges 3 and for all values of M'. Simulations performed over realistic indoor UWB channels are provided to verify the theoretical results.     

Impact of Ge-Sb-Te compound engineering on the set operation performance in phase-change memories

The phase-change memory (PCM) technology is considered as one of the most attractive non-volatile memory concepts for next generation data storage. It relies on the ability of a chalcogenide material belonging to the Ge-Sb-Te compound system to reversibly change its phase between two stable states, namely the poly-crystalline low-resistive state and the amorphous high-resistive state, allowing the storage of the logical bit. A careful study of the phase-change material properties in terms of the set operation performance, the program window and the electrical switching parameters as a function of composition is very attractive in order to enlarge the possible PCM application spectrum. Concerning the set performance, a crystallization kinetics based interpretation of the observed behavior measured on different Ge-Sb-Te compounds is provided, allowing a physics-based comprehension of the reset-to-set transition.     

Analysis and comparison of scheduling techniques for a BWA OFDMA mobile system

In the last few years the wireless metropolitan area networks (WMANs) have increased their popularity and attracted the interest of important research groups all over the world; as a consequence, several standards have been proposed. Among them, the IEEE 802.16 (WiMAX) is one of the most promising standard to carry out a full‐service broadband wireless network in an urban and suburban area. This standard provides high data rate within a wide coverage area with low implementation costs, possibility of multi‐traffic communications, and different network topologies. This paper deals with the analysis and performance comparison of different scheduling techniques for WiMAX networks for allowing quality of service (QoS) differentiation when different types of applications have to be supported and achieving a fair distribution of resource among users. In particular, the focus here is on the resource allocation problem for the case of mobile stations (MSs) active in an urban environment. The proposed scheduling algorithms exploit the orthogonal frequency division multiple access (OFDMA) scheme with adaptive modulation techniques in order to achieve a better network behavior. The performance of the proposed approaches will be derived here by means of theoretical analysis and computer simulations. Copyright © 2009 John Wiley & Sons, Ltd.