Jean-François Frigon

Universal-filtered multi-carrier technique for wireless systems beyond LTE

In this paper, we propose a multi-carrier transmission scheme to overcome the problem of intercarrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems. In the proposed scheme, called universal-filtered multi-carrier (UFMC), a filtering operation is applied to a group of consecutive subcarriers (e.g. a given allocation of a single user) in order to reduce out-of-band sidelobe levels and subsequently minimize the potential ICI between adjacent users in case of asynchronous transmissions. We consider a coordinated multi-point (CoMP) reception technique, where a number of base stations (BSs) send the received signals from user equipments (UEs) to a CoMP central unit (CCU) for joint detection and processing. We examine the impact of carrier frequency offset (CFO) on the performance of the proposed scheme and compare the results with the performance of cyclic prefix based orthogonal frequency division multiplexing (CP-OFDM) systems. We use computer experiments to illustrate the efficiency of the proposed multi-carrier scheme. The results indicate that the UFMC scheme outperforms the OFDM for both perfect and non-perfect frequency synchronization between the UEs and BSs.

Multi-antenna testbeds for research and education in wireless communications

Wireless communication systems present unique challenges and trade-offs at various levels of the system design process. Since a variety of performance measures are important in wireless communications, a family of testbeds becomes essential to validate the gains reported by the theory. Wireless testbeds also play a very important role in academia for training students and enabling research. In this article we discuss a classification scheme for wireless testbeds and present an example of the testbeds developed at UCLA for each of these cases. We present the unique capabilities of these testbeds, provide the results of the experiments, and discuss the role they play in an educational environment.

Multi(Six)-port impulse radio for ultra-wideband

Multi(six)-port impulse radio (MIR) validates the full channel (3-4 GHz) novel quaternary phase spectrum modulation (QPSM) scheme using a six-port modulator and demodulator circuits. Due to the lack of a monocycle generator, a 1-GHz spectral phase channel is generated from a rectangular pulse signal, upconverted using filters, mixer, and a local oscillator. The 3-4-GHz signal is applied to the RF input of a six-port modulator and digital data is simultaneously fed to a switch matrix terminating four ports of the modulator with either a short or open circuit. This operation produces an output signal in the QPSM scheme. One input port of the six-port demodulator is fed with the received phase-modulated signal and a second input port is fed with the reference nonmodulated signal. The demodulators four outputs provide signals of different amplitudes used to determine the modulation states with digital signal processing (DSP) algorithms. Modulation algorithms, demodulation algorithms, and synchronization control are implemented on a field-programmable gate-array-based DSP platform fitted with four analog-to-digital converters. Measurements and simulation results are presented to validate the MIR hardware and software in an operating 1-GHz ultra-wideband channel.

Improving the Reliability of Wireless Networks Using Cognitive Radios

To ensure widespread deployment and popularity, next generation wireless services will require a Quality of Service (QoS), and particularly a reliability, that is independent of the radio transmission medium. However, because of the failure-prone nature of wireless networks, providing a reliable communication link and guaranteeing a consistent QoS to users become key issues. In this tutorial, we describe the most common source of failures in wireless networks and provide a systematic failure classification procedure. Drawing from the vast literature on reliability in wireline networks, we then explain how cognitive radios can use their inherent capabilities to implement efficient prevention and recovery mechanisms to combat failures and thereby provide reliable communications and consistent QoS under all circumstances.

New-Wave Radio

Radio communications in the past century have relied primarily on nonlinear devices to modulate and demodulate signals for wireless transmissions. This article reviews initial laboratory results obtained with new radios using linear interferometers to modulate and demodulate ultra-wide-band (UWB) signals. Automotive and chip fabrication industries apply such interferometers in new commercial radios for UWB communications.

Dynamic radiation pattern diversity (DRPD) MIMO using CRLH leaky-wave antennas

This paper presents a dynamic radiation pattern diversity (DRPD) MIMO wireless system where the antennas radiation patterns are electronically controlled in real-time. The adopted antenna elements are composite right/left-handed (CRLH) microstrip leaky-wave (LW) antennas for which the beam direction can be electronically scanned in a continuous manner from backfire to endfire and the beam shape can be controlled. This system offers a tremendous amount of flexibility in tuning the channel transfer matrix to increase the system performance. Based on this architecture, we propose two simple radiation pattern control algorithms. The first one requires no feedback and averages out the channel fades while the second one requires a simple feedback at the receiver to select the beam pattern maximizing the performance metric. The capacity of both algorithms is derived and analyzed using Monte Carlo simulations. The results show that these algorithms significantly improve the wireless link outage performance in a slow fading environment and increase the diversity gain of a MIMO system for a fixed multiplexing gain.

Impact of Outdated Relay Selection on the Capacity of AF Opportunistic Relaying Systems with Adaptive Transmission over Non-Identically Distributed Links

In this paper, we derive probability density function (PDF) and cumulative distribution function (CDF) expressions for the end-to-end signal-to-noise ratio (SNR) of an opportunistic relaying amplify-and-forward (AF) cooperative diversity system over independent and non-identically distributed (i.ni.d.) Rayleigh fading links where outdated channel state information (CSI) is used for relay selection. Based on these expressions, we derive the analytical capacity and outage probability expressions for four classical adaptive transmission techniques, namely, optimal power and rate adaptation (OPRA), constant power with optimal rate adaptation (ORA), channel inversion with fixed rate (CIFR) and truncated channel inversion with fixed rate (TIFR). Numerical evaluations results are presented showing the impact of relay selection with outdated CSI and i.ni.d. links on the performance of each adaptive transmission technique in AF opportunistic relaying systems.

Design and VLSI implementation for a WCDMA multipath searcher

The third generation (3G) of cellular communications standards is based on wideband CDMA. The wideband signal experiences frequency selective fading due to multipath propagation. To mitigate this effect, a RAKE receiver is typically used to coherently combine the signal energy received on different multipaths. An effective multipath searcher is, therefore, required to identify the delayed versions of the transmitted signal with low probability of false alarm and misdetection. This paper presents an efficient and novel WCDMA multipath searcher design and VLSI architecture that provides a good compromise between complexity, performance, and power consumption. Novel multipath searcher algorithms such as time domain interleaving and peak detection are also presented. The proposed searcher was implemented in 0.18 /spl mu/m CMOS technology and requires only 150 k gates for a total area of 1.5 mm/sup 2/ consuming 6.6 mw at 100 MHz. The functionality and performance of the searcher was verified under realistic conditions using a channel emulator.

Field measurements of an indoor high-speed QAM wireless system using decision feedback equalization and smart antenna array

This paper reports on field measurements of point-to-point indoor high-speed (10 Mbit/s to 30 Mbit/s at 5 Mbaud) wireless communications realized using a flexible multilevel quadrature amplitude modulation (M-QAM) testbed that features real-time equalization and smart antenna-array technology. The results from an extensive set of measurements, 59262 trials in all, performed without cochannel interference under various receiver configurations and wireless environments are presented and analyzed. The results underscore the dramatic potential for a system that optimally combines equalization and a smart antenna array. For example, using only 10 mW of transmit power, the system delivered 30 Mitts at an uncoded bit error rate (BER) of 10/sup -3/ with 5% outage at a coverage radius of 20 in. For a lower data rate of 10 Mbitts, the coverage radius was increased to 32 in, the uncoded BER dropped below 10/sup -7/, and the outage improved to 1%. The field measurements indicate that a 4-tap feedforward-filter decision-feedback equalizer with eight feedback-filter taps is sufficient to mitigate the intersymbol interference for typical indoor environments. They also show a significant gain when using a smart antenna array. For example, when transmitting between rooms at a 2% outage probability, the signal-to-noise ratio (SNR) improves by 8.3 dB when using two antennas instead of one antenna. Doubling the number of antennas to four provided an additional SNR improvement of 5.2 dB. The paper also presents simulation results that confirm the performance trends observed from the field measurements.

A pseudo-Bayesian Aloha algorithm with mixed priorities for wireless ATM

In reservation MAC protocols, before obtaining a contention free access to the channel, a mobile must wait for its request packet to be successfully sent to the base station. A pseudo-Bayesian Aloha algorithm with multiple priorities is proposed in this paper to reduce the waiting time of delay sensitive request packets in a multimedia environment. Packets are transmitted in each slot according to a transmission probability based on the channel history and a priority parameter assigned to their priority class. An adaptation of the slotted protocol to the framed environment is also described. Simulation results are presented and show that the protocol offers a significant delay improvement for high priority packet with both Poisson and self-similar traffic while low priority packets only experience slight performance degradation.