Liesbet Van der Perre

Challenges and enabling technologies for energy aware mobile radio networks

Mobile communications are increasingly contributing to global energy consumption. In this article, a holistic approach for energy efficient mobile radio networks is presented. The matter of having appropriate metrics and evaluation methods that allow assessing the energy efficiency of the entire system is discussed. The mutual supplementary saving concepts comprise component, link and network levels. At the component level the power amplifier complemented by a transceiver and a digital platform supporting advanced power management are key to efficient radio implementations. Discontinuous transmission by base stations, where hardware components are switched off, facilitate energy efficient operation at the link level. At the network level, the potential for reducing energy consumption is in the layout of networks and their management, that take into account slowly changing daily load patterns, as well as highly dynamic traffic fluctuations. Moreover, research has to analyze new disruptive architectural approaches, including multi-hop transmission, ad-hoc meshed networks, terminal-to-terminal communications, and cooperative multipoint architectures.

WLC10-5: Performance Analysis of Slotted Carrier Sense IEEE 802.15.4 Medium Access Layer

The IEEE 802.15.4 standard defines the medium access control (MAC) and physical layer for sensor networks. One of the MAC schemes proposed is slotted carrier sense multiple access with collision avoidance (CSMA/CA), and this paper analyzes whether this scheme meets the design constraints of low-power and low-cost sensor networks. The paper provides a detailed analytical evaluation of its performance in a star topology network for both saturated and unsaturated periodic traffic.The form of the analysis is similar to that of Bianchi for IEEE 802.11 DCF only in the use of a per user Markov model to capture the state of each user at each moment in time. The key assumptions to enable this important simplification and the coupling of the per user Markov models are however different, as a result of the very different designs of the 802.15.4 and 802.11 carrier sensing mechanisms. The performance predicted by the analytical model is very close to that obtained by simulation. Throughput and energy consumption analysis is then performed and design guidelines are derived.

Distributed cognitive coexistence of 802.15.4 with 802.11

Thanks to recent advances in wireless technology, a broad range of standards are currently emerging. Interoperability and coexistence between these heterogeneous networks are becoming key issues, which require new adaptation strategies to avoid harmful interference. In this paper, we focus on the coexistence of 802.11 Wireless LAN and 802.15.4 sensor networks in the ISM band. Those networks have very different transmission characteristics that result in asymmetric interference patterns. We propose distributed adaptation strategies for 802.15.4 nodes, to minimize the impact of the 802.11 interference. This interference varies in time, frequency and space and the sensor nodes adapt by changing their frequency channel selection over time. Different distributed techniques are proposed, based on scanning (with increasing power cost) on the one hand, and based on increased cognition through learning on the other hand. These techniques are evaluated both for performance and energy cost. We show that it is possible to achieve distributed frequency allocation approaches that result only in an increase of 20% of the delay performance compared to ideal frequency allocation. Moreover, it is shown that a factor of two in energy consumption can be saved by adding learning to the system

Architectures for cognitive radio testbeds and demonstrators — An overview

Wireless communication standards are developed at an ever-increasing rate of pace, and significant amounts of effort is put into research for new communication methods and concepts. On the physical layer, such topics include MIMO, cooperative communication, and error control coding, whereas research on the medium access layer includes link control, network topology, and cognitive radio. At the same time, implementations are moving from traditional fixed hardware architectures towards software, allowing more efficient development. Today, field-programmable gate arrays (FPGAs) and regular desktop computers are fast enough to handle complete baseband processing chains, and there are several platforms, both open-source and commercial, providing such solutions. The aims of this paper is to give an overview of five of the available platforms and their characteristics, and compare the features and performance measures of the different systems.

High-Throughput, Low-Power Software-Defined Radio Using Reconfigurable Processors

A new, low-power software-defined radio baseband supports up to 600 Mbps. Wireless LAN and WiMax are implemented on a dynamically reconfigurable processor thats fully utilized in the baseband operation. Power is estimated at 500 mW in a 40-nm CMOS design. The platform also permits fast runtime switching between multiple wireless standards.

Air Interface and Physical Layer techniques for 60 GHz WPANs

Thanks to the unprecedented availability of huge bandwidth, the capacity offered by wireless systems in the 60 GHz band can exceed the mythical barrier of 1 Gbps wireless, enabling the deployment of new applications. However, the performance can be limited by the non-ideality of the analog front-ends, multipath fading and the difficulty to achieve a reasonable link budget at high data rates. The goal of this paper is to introduce high rate communications in the 60 GHz band and the associated challenges. We will first introduce WPANs in the 60 GHz band, describing the possible applications, the propagation channel and the standardization context. Furthermore, based on the characteristics of the propagation channel, we will show that beamforming is desirable to boost the link budget, reduce interference and, in some cases, reduce multipath. Next, we will introduce candidate PHY layer solutions that at the same time meet the throughput requirements and relax the analog front-end design. Our solutions rely on the combination of block transmission combined with (nearly) constant envelope modulation: this provides low peak-to-average power ratios, easy equalization, good spectral properties and modest front-end requirements in terms of phase noise and ADC resolution. The receiver signal processing associated with the modulation techniques will be described and link level simulation results will be provided, highlighting the front-end friendliness of the modulation technique

Overview of a Software Defined Downlink Inner Receiver for Category-E LTE-Advanced UE

With the soaring development cost of deep sub-micron silicon and the fast-growing diversity in wireless communications, software defined baseband becomes more and more important for handheld devices. However, most software defined receivers reported in previous literatures are still far away from fulfilling the requirement of emerging wireless standards such as the LTE-Advanced. The category-E User Equipment (UE) defined in LTE-Advanced, as the most demanding category for handheld devices, requires processing 2 concurrent data streams at around 300Mbps aggregated throughput. It is not clear whether SDR baseband processors can tackle this challenge. In our work, we explore the feasibility for software defined baseband for LTE-Advanced. With a highly customized SDR baseband processor, we have recently accomplished a software defined downlink inner receiver for Category-E LTE-Advanced UE. The implemented inner receiver includes fully fledged synchronization and data detection functionalities, including coarse CFO estimation/compensation, I/Q imbalance estimation/compensation, OFDMA demodulation, channel estimation, fine SCO/CFO estimation/compensation, MIMO channel processing, MIMO data detection and LLR generation. This paper is intended to bring an overview for the work and emphasizes key aspects that enable the feasibility of the work. In this paper, we will introduce the algorithm and processor architecture co-design flow, overall receiver functionalities, important optimizations and implementation results.

Computation-skip error resilient scheme for recursive CORDIC

Aggressive voltage and frequency scaling are widely utilized to exploit the design margin introduced by the process, voltage and environment variations. However, scaling beyond the critical voltage or frequency results to numerous timing errors, and hence unacceptable output quality. In this paper, a computation-skip (CS) scheme is proposed for recursive digital signal processors with a fixed cycles per instruction (CPI) to correct timing errors. A CORDIC processor with the proposed CS scheme still functions when scaling beyond the sub-critical voltage or frequency. It improves EVM by 47.9 dB at its most critical frequency or supply voltage, and extends the voltage scaling limit by 90 mV w.r.t the conventional CORDIC. Besides, it is more than 1.7X energy efficient w.r.t. the conventional high-speed CORDIC, which is designed for a more aggressive scaling.

Joint Compensation of IQ Imbalance, Frequency Offset and Phase Noise

Zero-IF receivers are gaining interest because of their potential to enable low-cost OFDM terminals. However, Zero-IF receivers introduce IQ imbalance which may have a huge impact on the performance. Rather than increasing component cost to decrease the IQ imbalance, an alternative is to tolerate the IQ imbalance and compensate it digitally. Current solutions require extra analog hardware or converge too slowly for bursty communication. Moreover, the impact of a frequency offset and phase noise on the IQ estimation/compensation problem is not considered. In this paper, we analyze the joint IQ imbalance-frequency offset-phase noise estimation and propose a low-cost, highly effective, all-digital compensation scheme. For large IQ imbalance ( ℯ= 10%, ΔΦ= 10°), large frequency offsets and in the presence of phase noise, our solution results in an average implementation loss below 1 dB. It therefore enables the design of low-cost, low-complexity OFDM receivers.

SDR platform for 802.11n and 3-GPP LTE

One of the key enablers for cheaper and faster time to market for next generation radios are software defined radios. However to reach an energy efficient but yet programmable solution for different radio standards, requires the designer to trade-off the right flexibility to programmability. In this paper we introduce IMECs SDR platform which is capable of running various wireless standards like: Wireless LAN, LTE, WiMAX etc. We illustrate the different components in the IMECs SDR solution.