Niels A. Moseley

Digitally Enhanced Software-Defined Radio Receiver Robust to Out-of-Band Interference

A software-defined radio (SDR) receiver with improved robustness to out-of-band interference (OBI) is presented. Two main challenges are identified for an OBI-robust SDR receiver: out-of-band nonlinearity and harmonic mixing. Voltage gain at RF is avoided, and instead realized at baseband in combination with low-pass filtering to mitigate blockers and improve out-of-band IIP3. Two alternative ¿iterative¿ harmonic-rejection (HR) techniques are presented to achieve high HR robust to mismatch: a) an analog two-stage polyphase HR concept, which enhances the HR to more than 60 dB; b) a digital adaptive interference cancelling (AIC) technique, which can suppress one dominating harmonic by at least 80 dB. An accurate multiphase clock generator is presented for a mismatch-robust HR. A proof-of-concept receiver is implemented in 65 nm CMOS. Measurements show 34 dB gain, 4 dB NF, and + 3.5 dBm in-band IIP3 while the out-of-band IIP3 is +16 dBm without fine tuning. The measured RF bandwidth is up to 6 GHz and the 8-phase LO works up to 0.9 GHz (master clock up to 7.2 GHz). At 0.8 GHz LO, the analog two-stage polyphase HR achieves a second to sixth order HR > 60 dB over 40 chips, while the digital AIC technique achieves HR > 80 dB for the dominating harmonic. The total power consumption is 50 mA from a 1.2 V supply.

A Two-Stage Approach to Harmonic Rejection Mixing Using Blind Interference Cancellation

Current analog harmonic rejection mixers typically provide 30-40 dB of harmonic rejection, which is often not sufficient. We present a mixed analog-digital approach to harmonic rejection mixing that uses a digital interference canceler to reject the strongest interferer. Simulations indicate that, given a practical RF scenario, the digital canceler is able to improve the signal-to-interference ratio by 30-45 dB.

A 400-to-900 MHz receiver with dual-domain harmonic rejection exploiting adaptive interference cancellation

Wideband direct-conversion harmonic-rejection (HR) receivers for software-defined radio aim to remove or relax the pre-mixer RF filters, which are inflexible, bulky and costly [1,2]. HR schemes derived from [3] are often used, but amplitude and phase mismatches limit HR to between 30 and 40dB [1,2]. A quick calculation shows that much more rejection is wanted: in order to bring harmonic responses down to the noise floor (e.g. −100dBm in 10MHz for 4dB NF), and cope with interferers between −40 and 0dBm, an HR of 60 to 100dB is needed. Also in terrestrial TV receivers and in applications like DVB-H with co-existence requirements with GSM/WLAN transmitters in a small telephone, high HR is needed.

A Spectrum Sensing Technique for Cognitive Radios in the Presence of Harmonic Images

Harmonic downmixing is an important effect that must be taken into account when performing sensitive spectrum sensing using direct-conversion receivers. When the local oscillator waveform contains harmonics of the fundamental frequency, the quadrature mixer in the receiver will downconvert RF signals found at these harmonics, termed harmonic images, in addition to the RF signals around the fundamental frequency. The harmonic images will be detected by power spectral density based sensing algorithms and will cause certain parts of the desired spectrum to be mistakenly flagged as occupied. Although harmonic downmixing is important to consider, it is an often negelected effect. This paper presents a harmonic rejection spectral sensing technique, that exploits two quadrature mixers. The mixers work with different LO frequencies, which decorrelate the harmonic images so that cross-correlation of their outputs renders an improved spectral estimate. In addition to rejecting the harmonic images, spurious signals entering the receiver through the analog baseband inputs was also be rejected. The frequency resolution of the spectral estimate is scalable and the rejection of the harmonic images increases 15 dB per 1000-fold increase of the correlation time. The complexity of the algorithm is analyzed and its performance is shown by means of simulations. The effect of I/Q imbalance is also taken into account.

A T-DAB Field Trial Using a Low-Mast Infrastructure

A novel low-mast low-power terrestrial digital audio broadcasting (T-DAB) single frequency network topology is described and evaluated in this paper. For this purpose, a pilot network (band III and L-band) was constructed in Amsterdam, the Netherlands. The performance of the band III pilot network (channel 12B) is compared with the existing traditional high-power high-mast T-DAB network (channel 12C) of the public service broadcaster. An important goal is to investigate whether the pilot network can co-exist with an existing traditional T-DAB network. The field trial shows that a gap filler can effectively neutralize the adjacent channel interference of the pilot network on the existing T-DAB network. Moreover, the L-band pilot network is compared with both band III networks by assessing the indoor coverage of every network. For estimation of the indoor coverage, 34 objects were investigated. Both the indoor penetration loss for band III and L-band was determined for each object. Indoor coverage in a region is reached if 95% of the buildings or more have indoor coverage. Using this definition, the loss for band III is 21.6 dB and for L-band 24.6 dB. As a result we consider the indoor penetration loss values reported in literature as too optimistic. Also other parameters of the pilot network were measured, such as the frequency re-use distance.

Proteus II: design and evaluation of an integrated power-efficient underwater sensor node

We describe the design and evaluation of an integrated low-cost underwater sensor node designed for reconfigurability, allowing continuous operation on a relatively small rechargeable battery for one month. The node uses a host CPU for the network protocols and processing sensor data and a separate CPU performs signal processing for the ultrasonic acoustic software-defined Modulator/Demodulator (MODEM). A Frequency Shift Keying- (FSK-) based modulation scheme with configurable symbol rates, Hamming error correction, and Time-of-Arrival (ToA) estimation for underwater positioning is implemented. The onboard sensors, an accelerometer and a temperature sensor, can be used to measure basic environmental parameters; additional internal and external sensors are supported through industry-standard interfaces (I2C, SPI, and RS232) and an Analog to Digital Converter (ADC) for analog peripherals. A 433 MHz radio can be used when the node is deployed at the surface. Tests were performed to validate the low-power operation. Moreover the acoustic communication range and performance and ToA capabilities were evaluated. Results show that the node achieves the one-month lifetime, is able to perform communication in highly reflective environments, and performs ToA estimation with an accuracy of about 1-2 meters.

Experiments with aLS-Coop-Loc cooperative combined localization and time-synchronization

Performing real world experiments with underwater communication is difficult and time-consuming. Input for evaluation of localization and time-synchronization derived from experiments is not readily available. Using real-world experiments we evaluate the performance of our cooperative combined localization and time-synchronization approach called aLS-Coop-Loc and a non-cooperative approach. We perform experiments using the SeaSTAR Proteus node and a Commercial Off-the-Shelf (COTS) node from Kongsberg Maritime at a lake and at Strindfjorden in Norway. These experiments provide realistic insight into ranging performance in real-world environments. Evaluation shows that the cooperative approach outperforms non-cooperative approaches in terms of accuracy of localization and time-synchronization. aLS-Coop-Loc provides about about 2% to 34% better position accuracy and 50% improved time-synchronization.

Interference Rejection in Receivers by Frequency Translated Low‐Pass Filtering and Digitally Enhanced Harmonic‐Rejection Mixing

Software-Defined Radio (SDR) and Cognitive Radio (CR) concepts have recently drawn considerable interest. These radio concepts built on digital signal processing to realize flexibly programmable radio transceivers, which can adapt in a smart way to their environment. As CMOS is the mainstream IC technology for digital, we would also like to realize SDR and CR radio transceivers in CMOS. Attempts are being made to integrate the functionality of multiple dedicated narrowband radios into one radio chip, which is reconfigurable by software [1, 2]. This is hoped to bring cost and size reductions while supporting an ever increasing set of communication standards in a single device. The SDR concept might also allow field upgradable radios to accommodate evolving standards or cognitive radios to improve the efficiency of spectrum use [3].