Shiann-Shiun Jeng

Experimental evaluation of smart antenna system performance for wireless communications

In wireless communications, smart antenna systems (or antenna arrays) can be used to suppress multipath fading with antenna diversity and to increase the system capacity by supporting multiple co-channel users in reception and transmission. This paper presents experimental results of diversity gain, interference cancellation, and mitigation of multipath fading obtained by using a smart antenna system in typical wireless scenarios. Also given are experimental results for the signal-to-interference ratio (SIR) of two moving users, comparing different beamforming algorithms in typical wireless scenarios. All of the experiments were performed using the 900-MHz smart antenna testbed at The University of Texas at Austin.

Experimental studies of spatial signature variation at 900 MHz for smart antenna systems

A spatial signature is the response vector of a base-station antenna array to a mobile unit at a certain location. Mobile subscribers at different locations exhibit different spatial signatures. The exploitation of spatial diversity (or the difference of spatial signatures) is the basic idea behind the so-called space-division multiple-access (SDMA) scheme, which can be used to significantly increase the channel capacity and quality of a wireless communication system. Although SDMA schemes have been studied by a number of researchers, most of these studies are based on theoretical analyses and computer simulations with ideal assumptions. Not much experimental study, has been reported on spatial signature variation due to nonideal perturbations in a real wireless communication environment. The purpose of this paper is to present, for the first time, extensive experimental results of spatial signature variation using a smart antenna testbed. The results presented include the spatial signature variation with time, frequency, small displacement, multipath angle spread and beamforming performance. The experimental results show the rich spatial diversity and potential benefits of using an antenna array for wireless communication applications.

Experimental direction of arrival and spatial signature measurements at 900 MHz for smart antenna systems

Smart antenna systems which utilize adaptive beamforming techniques on both uplink and downlink transmissions will allow mobiles located at shorter reuse distances and mobiles located at spatially distinct angles from the base station to operate on the same frequency channel, thus providing significant capacity increase over conventional antenna. This paper presents some preliminary results of experimental studies of smart antenna systems for wireless communications. The purpose of this paper is to investigate the change in DOAs and spatial signatures of stationary moving transmitters to provide some insight into the advantages of DOA-based beamforming over spatial signature beamforming for downlink transmissions.

Evaluation of beamforming algorithm effectiveness for the smart wireless LAN system

The smart wireless LAN (SWL) system integrates the space-division-multiple-access (SDMA) technique with the IEEE 802.11 wireless LAN standard to enable multiple users to transmit on a wireless LAN at the same time in the same frequency band. Four beamforming algorithms are studied which the SWL system can use to minimize the interference that each user experiences from the other users. Computer simulations of the signal-to-interference (SIR) performance of the four beamforming algorithms are presented, and their SIR results are compared with results from previous experiments. Simulation results for the complete SWL physical layer are presented and analyzed.

Experimental evaluation of smart antenna system performance for capacity improvement

In wireless communications, smart antenna systems (or antenna arrays) can be used to increase system capacity by supporting multiple co-channel users in reception and transmission. In addition, the system capacity is limited by the signal-to-interference ratio (SIR), which can be significantly improved by the smart antenna system, providing another boost to the capacity. This paper presents experimental results for the SIR of two moving users, comparing different beamforming algorithms in typical wireless scenarios. The experiments were performed using the 900 MHz smart antenna testbed at The University of Texas at Austin.

Evaluation of Dynamic Slot Allocation Algorithms for the Smart Wireless LAN System

Conventional wireless LAN (WLAN) protocols such as IEEE 802.11 allow only one user to transmit at a time in a frequency band. The Smart Wireless LAN (SWL) system adapts smart antenna systems for WLANs to enable multiple WLAN users to transmit simultaneously in a frequency band. Dynamic slot algorithms are used by SWL to improve transmission quality and maximize capacity by selecting users for time slots based on their unique spatial signatures (SS). These types of algorithms have not been studied much for conventional WLANs because only one user is allowed to transmit per time slot in those systems, eliminating the need for slot assignment. The simulation results, showing the tradeoffs of the various algorithms studied, are presented and analyzed. Experimental results studying the stability of the SS for a stationary transmitter and the variation of the SS with displacement are presented, and show the feasibility of using smart antennas with WLAN systems.

Experimental evaluation of fading reduction and diversity gain for smart antenna systems

In wireless communications, the smart antenna systems (or antenna arrays) can be used to suppress multipath fading effects with antenna diversity and to increase system capacity by supporting multiple co-channel users in reception and transmission. This paper presents experimental results of diversity gain and mitigation of multipath fading obtained by using a smart antenna system in typical wireless scenarios.

Performance enhancement by applying FPTC and Franks windowing in DVB-T receiver

This paper presents the mobile receiving performance based on measured DVB-T signals. During mobile reception, the OFDM system suffers ICI because of time- varying channel. In this paper, the ICI effect is reduced in time domain utilizing the ISI-free region by using receiver windowing method with Franks window coefficients. The partial ensemble correlation symbol timing synchronization algorithm is applied here for its smaller timing estimation error and also estimates the ISI-free region. A time domain channel estimation method, frequency-domain pilot time- domain correlation (FPTC), is applied to estimate channel impulse response. The results show that using FPTC channel estimation method with Franks windowing method improves the mobile receiving performance. The performance improvement is verified through the demodulated constellation.

Evaluation of the timing synchronization algorithms for the smart wireless LAN system

The smart wireless LAN (SWL) system integrates smart antenna systems with spread spectrum wireless LAN (LAN) systems such as IEEE 802.11 to enable multiple WLAN users to transmit simultaneously in a frequency band. This advantage creates a potential problem because the 802.11 standard requires that all users use the same spreading code, so a straightforward application of the 802.11 standard could result in the loss of the 10 dB of spreading gain achieved by each user. The timing synchronization algorithms studied in this paper enable multiple (up to 11) users to use the same spreading code without a loss of the spreading gain. Two complimentary algorithms, with and without sorting, are studied here and their simulation results are analyzed.