Steve Carl Jamieson Parker

On capacity-optimal precoding for multiple antenna systems subject to EIRP restrictions

Ultra wideband transceivers promise multi-gigabit per second performance at power consumptions commensurate with portable devices. Future products are likely to adopt multiple antennas to maximize performance. Severe FCC EIRP restrictions impose an interesting system design constraint. In this paper, capacity optimal multiple antenna transmission schemes are investigated for EIRP restricted systems under the assumption that the channel is known at the transmitter. It is shown that per subcarrier antenna power allocation, which reduces to antenna selection at low SNR or when using one receive antenna, is optimal for some transmitter configurations. The improvements in capacity are quantified for representative channels.

Analysis of frequency-offset tracking in MIMO OFDM systems

This paper presents an analysis of frequency-offset estimation in multiple-input multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) systems. Tracking of the frequency offset between a transmitter and a receiver is often aided by transmitting pilots embedded in the data payload of a packet. The extension to multiple-antenna OFDM systems means that spatial beamforming will occur when transmitting pilots from all antennas simultaneously, which can reduce the robustness of frequency-offset estimation. This paper presents a thorough analysis of the spatial beamforming problem, and shows how the spatial correlation of the MIMO channel impacts performance. Simulation results are presented for both synthetic and measured channels, which agree well with the theoretical results

Space-time codes for future WLANs: principles, practice, and performance

The mobility and ubiquitous access afforded by wireless local area networks (WLANs) and high-performance portable products promise to revolutionize the way we live, work, and play. However, sustained improvements in the throughput of WLANs, while also supporting robust long-range operation, requires the use of multiple antennas at both the mobile terminal and the access point. This article reviews the various space-time coding and decoding technologies employed for capitalizing on the increased capacity of the multiple-input multiple-output (MIMO) radio channel. Also described is a channel sounding campaign performed in the office environments used to scope the expected performance of these space-time codes in realistic deployments.

The performance and efficiency of envelope elimination and restoration transmitters for future multiple-input multiple-output wireless local area networks

The inefficiency of contemporary power amplifiers (PAs), when operating in their linear region, is a major obstacle to mobile operation of wireless local area networks (WLANs) based on IEEE 802.11n. Therefore the use of more efficient envelope elimination and restoration (EER) transmitter architectures is considered. In addition to high efficiency it is also necessary to satisfy the spectral mask and achieve satisfactory link-level performance. Link-level simulations of a contemporary WLAN PA show that, at the power back-offs necessary to achieve sufficient linearity, the power added efficiency (PAE) is only ~1% for a system with four transmit antennas. In contrast, simulations of a phase feedback EER PA architecture show that it is possible to achieve an average PAE of 70%, while satisfying the spectral mask, with only a small degradation in link-level performance.

Antenna Selection with Phase Precoding for High Performance UWB Communication with Legacy WiMedia Multi-Band OFDM Devices

Ultra wide-band (UWB) devices conforming to the WiMediareg specification are set to become ubiquitous, with the adoption of WiMedia for wireless USB and Bluetooth 3.0. However, the performance of these devices at high data rates may be poor, as they operate at low signal powers and experience frequency selective fading. This paper therefore proposes a new transceiver design for improving the robustness and mean throughput when communicating with these devices. Performance is improved using multiple antennas, in conjunction with per subcarrier antenna selection based on channel state information at the transmitter. Legacy compliance is accomplished by using phase precoding to make transmissions appear to have originated from a single antenna system, albeit one with an associated channel that exhibits significantly reduced fading. Performance is benchmarked against legacy operation; and the impact of channel estimation and hardware calibration errors is investigated. Results show that, even with pessimistic assumptions about calibration errors, performance is improved dramatically.

Improved EER transmitters for WLAN

The envelope elimination and restoration (EER) transmitter architecture is capable of providing high power efficiency without compromising linearity. This paper shows that for a wireless local area network (WLAN) application, the envelope reconstruction process modulates the supply voltage of the switching amplifier over a large dynamic range. This introduces sufficient nonlinearity to violate emission specifications. Fortunately, the EER architecture can be improved by applying envelope and phase feedback. The phase feedback architecture satisfies the emission specifications of IEEE 802.11a, while envelope feedback provides modest adjacent channel power ratio (ACPR) improvement. The impact of clipping on the ACPR and error vector magnitude (EVM) is also investigated. It is shown that for a WLAN application, a clipping of only 1 dB can be tolerated before the output signal is degraded significantly.

Frequency offset tracking for MIMO OFDM systems using pilots

This paper presents an analysis of frequency offset estimation in MIMO OFDM systems. Tracking of frequency offsets is often aided by pilots transmitted in the data payload of a packet. The extension to multiple antenna OFDM systems means that spatial beamforming will occur when transmitting pilots from all antennas simultaneously, which can reduce the robustness of frequency offset estimation. We present a thorough analysis of the spatial beamforming problem and show how the spatial correlation of the MIMO channel impacts the performance. Simulation results are presented for measured channels recorded in an office environment, which agree well with the theoretical results.