Boris Come

Compensation of IQ imbalance and phase noise in OFDM systems

Nowadays, a lot of effort is spent on developing inexpensive orthogonal frequency-division multiplexing (OFDM) receivers. Especially, zero intermediate frequency (zero-IF) receivers are very appealing, because they avoid costly IF filters. However, zero-IF front-ends also introduce significant additional front-end distortion, such as IQ imbalance. Moreover, zero-IF does not solve the phase noise problem. Unfortunately, OFDM is very sensitive to the receiver nonidealities IQ imbalance and phase noise. Therefore, we developed a new estimation/compensation scheme to jointly combat the IQ imbalance and phase noise at baseband. In this letter, we describe the algorithms and present the performance results. Our compensation scheme eliminates the IQ imbalance based on one OFDM symbol and performs well in the presence of phase noise. The compensation scheme has a fast convergence and a small residual degradation: even for large IQ imbalance, the overall system performance for an OFDM-wireless local area network (WLAN) case study is within 0.6 dB of the optimal case. As such, our approach greatly relaxes the mismatch specifications and thus enables low-cost zero-IF receivers.

Non-reciprocal transceivers in OFDM/SDMA systems: impact and mitigation

Channel reciprocity is needed in SDMA or MIMO downlink pre-filtering when the channel knowledge is acquired in the uplink. We first show analytically that the non-reciprocity of the base station analog hardware, which is part of the channel, introduces a very high level of multi-user interference and quantify the effect of the non-reciprocity by means of simulations. We then propose a novel calibration technique at the base station that enables to compensate for the non-reciprocity and reduce the MUI to a negligible value while having a low implementation cost.

OFDM-MIMO WLAN AP front-end gain and phase mismatch calibration

The work presents a front-end gain and phase mismatch calibration scheme for OFDM-MIMO/TDD WLAN systems using transmit-processing, where complete channel reciprocity and calibration of the access point (AP) hardware is needed. Simulation results for a single-user 2/spl times/2 OFDM-MIMO system with QAM-64 modulation show that our calibration method can reduce the implementation loss to as little as 0.2 dB at a coded BER of 10/sup -5/ The calibration scheme has been implemented and demonstrated by IMEC.

SOP integration and codesign of antennas

The successful deployment of wireless systems requires the integration of small, cost-effective antennas while preserving a reasonable electrical performance in the required bandwidth. This paper begins with a short overview of the most important antenna characteristics, and then uses these to describe the minimum requirements and fundamental performance-size limits for electrically small integrated antennas. The performance-size tradeoff is further illustrated by the design of a planar integrated antenna for WLAN. Codesign guidelines are given to avoid parasitic coupling between the integrated antenna and RF circuits. A concluding comparison is made between on-chip and on-package integration of a small antenna for microwave and millimeter wave systems.

Wideband VCO with Simultaneous Switching of Frequency Band, Active Core and Varactor Size

As the tuning range of integrated LC VCOs increases, it becomes difficult to co-design the active negative resistance core and the varactor optimally for the complete frequency range. The VCO presented here solves this by adjusting the negative resistance with a switched active core. Also the VCO gain variations are counteracted by employing an analog varactor that can change in size. The implementation in 0.13mum CMOS shows a tuning range from 3.1 to 5.2 GHz, with a power consumption varying accordingly from 2.1 to 7.7 mA from a 1.2V supply. The measured phase noise is -118 dBc at 1 MHz from a 4-GHz carrier

OFDM-WLAN receiver performance improvement using digital compensation techniques

Zero-IF receiver architectures are preferred over superheterodyne solutions since their better integration capabilities result in cost advantages. However, zero-IF receivers present a set of analog non-idealities to the system designer. Among those, DC offsets, I/Q mismatch, phase noise, and limited dynamic range are the most challenging ones. For each or these imperfections, we propose digital compensation techniques that can either improve receiver performance considerably or allow a relaxation of the analog front-end specifications. Simulation results are presented for IEEE 802.11a-compliant receiver specifications.

Impact of front-end effects on the performance of downlink OFDM-MIMO transmission

The work presents the impact of analog front-end effects on the BER performance of MIMO/SDMA-OFDM downlink transmission using minimum mean-squared error transmit processing at the access point. The implementation loss due to gain and phase mismatch, analog filtering, clipping and quantization, phase noise, and I/Q mismatch in the front-ends is given.

Single-package 5GHz WLAN RF module with embedded patch antenna and 20dBm power amplifier

The demanding requirements of emerging telecom standards compel designers to conceive transceivers that integrate building blocks designed in different technologies. Such heterogeneous systems, together with the need for miniaturization, require packaging and integration techniques more involved than all current reported work. By combining a thin-film technology on a glass substrate (MCM-D) with laminates for the ball grid array (BGA) package, we can integrate, in a single package, a 5 GHz WLAN RF module. The package includes a BiCMOS IC, a GaAs power amplifier (PA) with 20 dBm output compression, a GaAs TX/RX switch with 1 dB insertion loss, high-quality integrated RF filters and a patch antenna with more than 80% efficiency.

Fully reconfigurable active-Gm-RC biquadratic cells for software defined radio applications

The 4th generation of wireless systems needs low-power integrated transceivers that can be reconfigured in order to satisfy different standard requirements. Standard analog blocks are often not suitable for this step towards the future because of their lack of flexibility. We defined a novel approach to make active-Gm-RC biquadratic cells completely reconfigurable. The biquad provides digitally programmable bandwidth and hence power consumption with a fully customizable cut-off frequencies range. Besides, the noise level can be conveniently modified leading to a further power saving. We exemplified the use of this basic building block in the design of a flexible low-pass filter for a zero-IF transceiver. A 2nd/4th/6th order Butterworth filter was implemented with a continuous cut-off frequency tuning between 330 KHz and 24.6 MHz and with a current consumption range between 0.6mA to 26mA

MEMS-Enabled Dual-band 1.8 & 5-6GHz Receiver RF Front-end

This paper presents, for the first time, a MEMS-enabled dual-band receiver front-end in 0.13-mum CMOS, which covers both 1.8-GHz and 5-6-GHz bands. A packaged MEMS series switch is used to tune the LNAs input impedance for narrow-band matching in each of these bands. The mixer of the front-end is a double-balanced folded Gilbert cell, which is followed by a programmable current-output stage. The front-end shows a measured gain of 45 dB and a NF of 4.2 dB at 1.85 GHz. The LNAs IIP3 is -9 dBm at 1.85 GHz. The front-end consumes 28 mA from a 1.2-V power supply