Rod Walton

A high-performance MIMO OFDM wireless LAN

Tremendous consumer interest in multimedia applications is fueling the need for successively higher data rates in wireless networks. Data rates in wireless wide area networks are limited by the need to address wide coverage, vehicular mobility, and the limitations of licensed spectrum. Thus, data rates in WWANs continue to lag advances in wireless local area networks by orders of magnitude. There are valuable lessons to be learned from the design of WLANs that provide data rates in excess of hundreds of megabits per second. Several technologies are instrumental in enabling the future of high-performance WWANs, including multiple transmit and receive antennas, OFDM, closed loop transmission control, and low-latency MAC operation. We describe a MIMO WLAN design and prototype that exploits these attributes to provide data rates in excess of 200 Mb/s above the MAC

Packet error probability prediction for system level simulations MIMO-OFDM based 802.11n WLANs

A method for predicting packet error rates in MIMO-OFDM WLAN systems is presented. The method is based on using post-detection SNRs as an abstraction of the physical layer, and is motivated by the need for a simple and efficient way of modelling the physical layer in system level simulation scenarios involving multiple stations. The physical layer abstraction is sufficient for generating error processes in the system simulations that accurately reflect the interaction between the MIMO-OFDM physical layer and the underlying wireless channel. We validate the abstract model by comparing packet error rates predicted by the model with packet error rates obtained through full link simulations for two different approaches to MIMO processing, referred to as spatial spreading and eigenvector steering.

A Comparison of MIMO Receiver Structures for 802.11N WLAN - Performance and Complexity

This paper compares the performance and complexity of various MIMO receiver structures for 802.11n WLAN systems, including linear approaches such as MMSE and ZF, and iterative detection and decoding using list sphere decoding. Optimal beam steering with the low-complexity MMSE receiver is shown to outperform the computationally-expensive list sphere decoder receiver with an uninformed transmitter

CDMA downlink performance issues

Several key performance issues for the downlink of IS-95 based CDMA systems are explored. Performance data collected from a number of operational systems using CDMA diagnostic monitor equipment and post-processing analysis software is used to aid in the development of improved link and system performance prediction models. The models developed permit the sensitivity of link performance and system capacity to be examined for a wide variety of deployment scenarios. The impact of orthogonality loss on link performance is assessed along with the relative impact on system capacity. Performance limitations resulting from channel induced multipath and soft handoff are also examined based on using a 3-tap RAKE receiver. The results suggest that many systems may not meet the performance and capacity predictions derived from using simplistic downlink radio network planning models.

Transmission strategies for high throughput MIMO OFDM communication

This paper presents two transmission techniques for MIMO OFDM communication, referred to as spatial spreading and eigenvector steering. Spatial spreading is used when the transmitting station is not presumed to have sufficient channel state information to compute optimum steering vectors. This situation may occur for a variety of reasons, including poor or aged channel estimates or lack of calibration between the transmit and receive antenna chains. Eigenvector steering is used in cases where the transmitting station has sufficient information about the channel to compute optimum transmit steering vectors. Simulation results showing throughput and range achieved by the two transmission strategies are provided.

Results from MIMO channel measurements

Statistics and system performance results derived from the outdoor measurements performed with a true multiple-input-multiple-output (MIMO) wideband channel measurement system are presented. These results are applicable to the MIMO channel modeling particularly for a model with paths at different time delays (tapped-delay line model) and an associated correlation matrix for each time delay.

Performance of a multi-rate CDMA packet data system

The performance of a multi-rate IS-95 based CDMA packet data system is examined. Both the uplink and downlink channels are analyzed in a multi-user, multi-rate environment for a single 1.25 MHz carrier. On the uplink, the throughput-delay performance is evaluated for a connectionless access protocol. On the downlink, the throughput-delay performance is derived by applying standard queuing models to simulation results describing the system throughput. Load control policies are presented for both links along with simulated performance data. The results demonstrate that the multi-rate CDMA packet data system can deliver more than twice the net throughput of voice services with the same spectral efficiency.