John R. Farserotu

Principles and limitations of ultra-wideband FM communications systems

This paper presents a novel UWB communications system using double FM: a low-modulation index digital FSK followed by a high-modulation index analog FM to create a constant-envelope UWB signal. FDMA techniques at the subcarrier level are exploited to accommodate multiple users. The system is intended for low (1–10 kbps) and medium (100–1000 kbps) bit rate, and short-range WPAN systems. A wideband delay-line FM demodulator that is not preceded by any limiting amplifier constitutes the key component of the UWBFM receiver. This unusual approach permits multiple users to share the same RF bandwidth. Multipath, however, may limit the useful subcarrier bandwidth to one octave. This paper addresses the performance with AWGN and multipath, the resistance to narrowband interference, as well as the simultaneous detection of multiple FM signals at the same carrier frequency. SPICE and Matlab simulation results illustrate the principles and limitations of this new technology. A hardware demonstrator has been realized and has allowed the confirmation of theory with practical results.

Low-Complexity Ultra-Wide-Band Communications

Low-complexity low-power ultra-wide-band (UWB) radios are required for low data rate (LDR, < 100 kbps) short- range applications. Potential low-power air interface candidates are impulse radio UWB and FM-UWB. The use of simple (noncoherent) radio architectures, a low supply voltage and duty cycling pave the way to low power consumption. Interference mitigation is an important requirement for todays UWB receivers. Processing gain and filtering may be applied in the physical layer, whereas detect and avoid strategies work at MAC level. Constant-envelope FM-UWB uses high modulation index analog FM for spreading. Instantaneous despreading in the receiver, combined with processing gain make this system an interesting option for robust LDR personal area network systems.

A Short Range, Low Data Rate, 7.2 GHz-7.7 GHz FM-UWB Receiver Front-End

A 9 mW FM-UWB receiver front-end for low data rate ( <50 kbps), short range ( <10 m) applications operating in the ultra-wideband (UWB) band centered at 7.45 GHz is described in this paper. A single-ended-to-differential preamplifier with 30 dB voltage gain, a 1 GHz bandwidth FM demodulator, and a combined (preamp/demodulator) receiver front-end were fabricated in 0.25 mum SiGe:C BiCMOS and characterized. Measured receiver sensitivity is -85.8 dBm while consuming 9 mW from a 1.8 V supply, and -83 dBm consuming 6 mW at 1.5 V. 15-20 m range line-of-sight in an indoor environment is realized, justifying FM-UWB as a robust radio technology for short range, low data rate applications. Multi-user and interference capabilities are also evaluated.

Low-Complexity Ultra Wideband Communications

Low-complexity, low power UWB radios are required for LDR short-range applications. Potential low power air interfaces candidates are impulse radio UWB and FM-UWB. FM-UWB is a constant-envelope UWB communication system using double FM: digital FSK followed by high modulation index analog FM to create a constant-envelope UWB signal. The system is intended for low data rate (< 100 kbps), short-range (< 10 m) personal area network systems. Due to its simple architecture, FM-UWB radio will be low cost and have low power consumption

A Wideband FM Demodulator for a Low-Complexity FM-UWB Receiver

A wideband FM demodulator circuit for a low-complexity UWB communications system based upon double FM techniques is presented. The receiver demodulates the FM-UWB signal without frequency translation. The FM demodulator presented here covers the low band (3.1-5 GHz) and consumes 10 mW. The 0.72 mm2 demodulator IC is implemented in 0.18 mum Si-Ge BiCMOS technology

Multipath Behavior of FM-UWB Signals

This paper analyzes the multipath behavior of FM-UWB signals and more particularly the effect of frequency selective fading upon the sub-carrier signal level in the FM-UWB receiver. The performance with CM1-CM4 channels is investigated and illustrated with MATLAB simulation results. Good and bad propagation channels for FM-UWB communication systems are identified. The effect of frequency selective fading is mainly determined by the channel transfer at the edges of the FM-UWB signals bandwidth. It is shown that multipath is beneficial for the FM-UWB receiver performance.

On the multiple input multiple output capacity of Rician channels

We consider a wireless system with multiple antennas at both the transmitter and the receiver and operating in a Rician propagation environment. For fixed bandwidth and total transmitted power, the Rician channel matrix can be seen as the sum of two contributions. The first contribution is related to the deterministic component of the channel, which is given by the line-of-sight (LOS) path only. The second contribution denotes the stochastic component of the channel given by the Rayleigh fading paths, in which case the corresponding elements in the channel matrix are modeled as random variables. We focus on the averaged Rician channel capacity expression and its behavior according to the contribution of the deterministic and stochastic part of the channel. We derive an upper bound on the averaged Rician channel capacity and we show that a limit of this capacity is given by the sum of the capacities corresponding to the LOS and Rayleigh components when they are considered separately. Simulations results are given to support our claims.

UWB Transmission and MIMO Antenna Systems for Nomadic Users and Mobile PANs

Personal Area Networks (PANs) are expected to play an important role in future mobile communications and information systems. A proliferation of low data rate sensor and control devices is envisioned. These devices must be able to communicate across various networks in order to provide seamless end-to-end service. At the physical and link level, several factors are critical in order to realize a nomadic PAN: co-existence with other systems, efficient use of increasingly scarce spectrum resources and capacity, robustness in the presence of interference, as well as, the availability of low cost individual user devices. In this paper, we examine a concept for nomadic PANs employing low cost, low data rate ultra wideband (UWB) communication links between personal devices and a handset, or mobile bridge, coupled with a multiple input multiple output (MIMO) antennas for communication from a mobile bridge to other networks. Key issues are identified and potential capacity and quality-of-service (QoS) enhancements are evaluated.

FM-UWB: A Low-Complexity Constant Envelope LDR UWB Approach

This paper presents a novel low complexity, constant envelope UWB communication system for personal network and sensor network applications: FM-UWB. FM-UWB uses double FM: digital FSK followed by high modulation index analog FM to create a constant envelope UWB signal. FDMA techniques at the sub-carrier level may be exploited to accommodate multiple users. A wideband delay line FM demodulator that is not preceded by any limiting amplifier constitutes the key component of the FM-UWB receiver. This allows multiple users to share the same RF bandwidth. The system is intended for low data rate, short-range (< 10 m) applications. Due to its simple architecture, FM-UWB radio will be low cost and have low power consumption.

Impulse radio ultra-wideband ranging based on maximum likelihood estimation

We propose a high-resolution ranging algorithm for impulse radio (IR) ultra-WideBand (UWB) communication systems in additive white Gaussian noise. We formulate the ranging problem as a maximum- likelihood (ML) estimation problem for the channel delays and amplitudes at the receiver. Then we translate the obtained delay estimates into an estimate of the distance. The ML estimation problem is a non-linear problem and is hard to solve. Some previous works focus on finding alternative estimation procedures, for example by denoising. In contrast, we tackle the ML estimation problem directly. First, we use the same transformation as the first step of Iterative quadratic maximum likelihood (IQML) and we transform the ML problem into another optimization problem that avoids the estimation of the amplitude coefficients. Second, we solve the remaining optimization problem with a gradient descent approach (pseudo-quadratic maximum likelihood (PQML) algorithm). To demonstrate the good performance of the proposed estimator, we present the numerical evaluations under the IEEE 802.15.4a channel model. We show that our algorithm performs significantly better than previously published heuristics. We also derive a reduced complexity version of the algorithm algorithm, which will be implemented on the Xinlix field-programmable gate array (FPGA) board in the future. We test the approach in a real weak line of sight (LOS) propagation environment and obtained good accuracy for the ranging.