Garret Okamoto

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.

Multipath direction finding with subspace smoothing

Antenna arrays can be employed in mobile communications to increase channel capacity as well as communication quality via spatially selective reception/transmission at base stations. In most wireless communications systems, directions of arrival of multipath signals need to be found for spatial selective transmission. Unfortunately, due to the coherent nature of multipath signals, it is quite difficult to find their directions of arrival. In this paper, we will present a subspace smoothing algorithm for finding the directions of arrival of multipath signals based on the mobile terminal signals received at different time instances. More importantly, we will present our experimental results to demonstrate that the spatial diversity is present for slight movements of a mobile terminal and that the subspace smoothing approach is effective in real wireless scenarios. All of the experiments were performed using the smart antenna testbed at the University of Texas at Austin.

Throughput multiplication of wireless LANs: spread spectrum with SDMA

The bandwidth allocated for wireless LANs in the IEEE 802.11 standard is limited and the overall throughput is limited for multimedia services because base stations grant each node air time in a sequential manner. With exponentially growing demand for multimedia services, this limitation becomes a bottleneck for expanding wireless network capabilities. In this paper, we exploit another resource, i.e., space, and design a new spread spectrum space-division-multiple-access (SS-SDMA) protocol to achieve throughput multiplication and significant reduction of communication delays. The basic idea behind the SS-SDMA protocol is that it exploits spatial diversity among different terminals to selectively transmit and receive signals in the same time period and frequency band.

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.

Multimedia communications over wireless LANs via the SWL protocol

The transmission of multimedia data over networks has increased steadily over the past few years and this increase is projected to accelerate in the future. However, virtually all current products and research for multimedia traffic over networks have concentrated solely on transmission of multimedia applications to and from wired terminals. Excluding mobile terminals from multimedia applications such as voice clearly limits the flexibility and potential of those applications. Additionally, the bandwidth allocated for wireless LANs in the IEEE 802.11 standard is limited and overall throughput is limited, and these limitations will become a bottleneck for expanding wireless network capabilities. We exploit another resource, i.e., space, and design a new smart wireless LAN (SWL) protocol to achieve throughput multiplication and flexibility for mixed traffic networks. Experimental studies and computer simulations will show the feasibility and performance benefits for using SWL with wireless LANs, particularly for multimedia applications.

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.

The smart wireless LAN system: physical layer design and results

The smart wireless LAN (SWL) system integrates SDMA with the IEEE 802.11 wireless LAN standard to enable multiple users to transmit on a wireless LAN at the same time. The physical layer design of the SWL system allows for remote terminals to transmit and receive as specified in the 802.11 standard. The SWL base station uses an antenna array and SDMA techniques to simultaneously transmit and receive data from up to four terminals at once. Downlink is performed via a delay and combination at the base station while utilizing standard beamforming techniques. Uplink signals are separated and decoded at the base station using a simple pseudoinverse technique utilizing the spatial signature knowledge found previously. Experimental results demonstrate the feasibility of using SDMA in our wireless LAN scenario. Computer simulation results show the feasibility and potential of this method.

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.

Ultra low complexity adaptive beamforming via non-eigen decomposition

This paper presents a non-eigendecomposition based beamforming algorithm under the assumption that the power of the desired signal is large compared to the interfering signals. The algorithm provides a noise free suboptimal weight vector when the noise is spatially uncorrelated. and the weight vector is approximately equal to the desired signals spatial signature. The significance here is the substantial reduction in computational complexity. Total computational load for the weight vector is O(3M-2) per snapshot for a system with M receiving antennas by approximating the cross correlation vector of the received signals in the reference and other antennas. The weight vector is a function of only the cross correlation vector and initial guess and does not require a step size. This technique requires neither a training sequence nor an assumption of incoherency among impinging signals. The algorithm is derived analytically and simulations evaluate the CDMA capacity improvement and the tracking ability when the incident angle of the desired signal varies at each snapshot.