Performance comparison of differential space-time signalling schemes for OFDM systems

Differential transmit diversity is an attractive alternative to its coherent counterpart, especially for multiple antenna systems where channel estimation is more difficult to attain compared to that of single antenna systems. In this paper we compare two different types of differential transmit diversity techniques for OFDM based transmissions. The first technique uses differential space-time block codes (DSTBC) from orthogonal designs and the second uses the differential cyclic delay diversity (DCDD). The results compare the bit error performance for several transmit antenna configurations. The results show that DCDD offers a very close performance to that of DSTBC, with the advantage of a simplified receiver structure

Performance evaluation of a Bluetooth interference canceller in IEEE802.11b wireless networks

In this paper, we propose a narrowband interference canceller (NIC) to cancel Bluetooth interference occurring in IEEE 802.11b WLAN systems. The proposed NIC has a simple structure: an adaptive filter followed by a Rake receiver. The simulation results show that the proposed NIC can effectively cancel Bluetooth interference in an 802.11b receiver. Although an IEEE802.11b/Bluetooth framework is given as an example, the proposed NIC can be used in any spread spectrum system with frequency-hopping narrowband interference (FHNBI)

Smart antenna calibration: requirements and techniques

This paper presents a detailed analysis of the classes of distortion that degrade the performance of Smart Antennas. This uses the results of a Smart Antenna test bed to illustrate the impact of temperature on performance. A design technique that aide's calibration is then described

Calibration of smart antenna systems: measurements and results

Smart antennas (SAs) are viewed as a candidate enabling technology for modern wireless communication systems to increase network capacity and facilitate location-based services. By conducting measurements on an SA test-bed, the signal distortion introduced by the implementation of a practical system can be analysed. This distortion can have significant impact on the estimation of signal wavefronts. Measurements have been conducted at the system, sub-system and component levels, using an SA developed for this purpose and employing a uniform circular array. This has enabled the error introduced by an implemented system to be examined. Calibration procedures are developed to overcome these implementation limitations. The cause and effects of these errors are examined, and system manufacturing tolerances and temporal thermal effects on the analogue sub-systems are shown to be the major contributor to this error; these results are presented and analysed

Robust DoA estimation by extension of the SAGE algorithm: algorithm description and trails results

By extending the space-alternating generalised expectation-maximisation (SAGE) parameter estimation algorithm to include a novel cost variant process, the robustness of direction of arrival (DoA) estimation from the SAGE algorithm is shown to improve. A novel extension to the standard SAGE algorithm that enhances the parameter estimation process is first introduced. Field trials that have been conducted using an adaptive antenna to verify the performance of this algorithm are presented. Results show that the extended SAGE algorithm improves DoA performance compared to standard SAGE by 5°, when operating in an urban environment

Adaptive antennas: the calibration problem

Adaptive antennas are recognized as a means of increasing the performance of communications systems. However, practical realization of such systems relies on suitable calibration of distortion effects caused by the circuitry and antenna structures. This work presents a detailed analysis of the classes of distortion that degrade the performance of adaptive antennas. This uses the results of an adaptive antenna testbed employing an eight-element circular array to illustrate the impact of temperature on performance. Design techniques that aid calibration are then described. In particular, digital downconversion, array design, harmonic sampling, sample clock dither, and clock management are discussed as a means of designing an adaptive array with the calibration problem in mind

Cost-variant sage: field trails and results

By extending the Space-Alternating Generalised Expectation-Maximisation (SAGE) parameter estimation algorithm to include a novel cost variant process, the robustness of Direction of Arrival (DoA) estimation from the SAGE algorithm is shown here to improve. A novel extension to the standard SAGE algorithm that enhances the parameter estimation process is first introduced. Field trials that have been conducted using an adaptive antenna to verify the performance of this algorithm are presented. Results show the extended SAGE algorithm improves DoA performance compared to standard SAGE by 5deg when operating in an urban environment

Evaluation of IEEE 802.11b and Bluetooth coexistence in an office environment

IEEE 802.11b and Bluetooth (BT) have been comprehensively used as the core technologies of WLAN and WPAN respectively. However, since they both operate in the 2.4 GHz ISM frequency band, mutual interference between them can be significant. We evaluate the impact of BT interference on 802.11b systems in an office environment by a set of experiments. We include the experimental results that evaluate the narrowband interference problem in IEEE 802.11b networks; and we specify the attenuation requirement of interference suppression technologies utilised by the IEEE 802.11b system

Comparison of differential space-time block codes and differential cyclic delay diversity for a multi-carrier wireless system

Differential transmit diversity is an attractive alternative to its coherent counterpart, especially for multiple antenna systems where channel estimation is more difficult to attain compared to that of single antenna systems. In this paper we compare two different types of differential transmit diversity techniques for a multi-carrier based transmissions in particular OFDM. The first technique uses Differential Space-time Block Codes from orthogonal designs and the second uses Differential Cyclic Delay Diversity. The results present the bit error performance for several transmit antenna configurations. The results show that DCDD offers close performance to that of DSTBC with the advantage of simplified receiver