Karla Ziri-Castro

Prediction of variation in MIMO channel capacity for the populated indoor environment using a Radar cross-section-based pedestrian model

Multipath propagation is a fundamental requirement for the operation of multiple-input multiple-output (MIMO) wireless systems. However, at ultrahigh frequency (UHF) and above, pedestrian movement may significantly affect the multipath propagation conditions in indoor environments. For the first time, a systematic analysis of the effect of pedestrian movement on channel capacity for an otherwise line-of-sight MIMO link in a single room is presented. A novel channel model for the populated indoor environment is also introduced, based on geometrical optics and a detailed radar cross-section representation of the human body. The new model generates a temporal profile for the complex transfer function of each antenna combination in the MIMO system in the presence of specified pedestrian movement. Channel capacity values derived from this data are important in terms of understanding the limitations and possibilities for MIMO systems. Capacity results are presented for a 42-m/sup 2/ single room environment, using a 2.45-GHz narrowband 8/spl times/8 MIMO array with 0.4/spl lambda/ element spacing. Although the model predicts significant increases in the peak channel capacity due to pedestrian movement, the improvement in mean capacity values was more modest. For the static empty room case, the channel capacity was 10.9 b/s/Hz, while the mean capacity under dynamic conditions was 12.3 b/s/Hz for four pedestrians, each moving at the same speed (0.5 m/s). The results presented suggest that practical MIMO systems must be sufficiently adaptive if they are to benefit from the capacity enhancement caused by pedestrian movement.

Prediction and Measurement of Multiuser MIMO-OFDM Channel in Rural Australia

Commonwealth Scientific and Industrial Research Organisation (CSIRO) has recently conducted a technology demonstration of a novel fixed wireless broadband access system in rural Australia. The system is based on multi-user multiple-input multiple-output orthogonal frequency division multiplexing (MU-MIMO-OFDM). It demonstrated an uplink of six simultaneous users with distances ranging from 10 m to 8.5 km from a central tower, achieving 20 bits/s/Hz spectrum efficiency. This paper reports on the analysis of channel capacity and bit error probability simulation based on the measured MU-MIMO-OFDM channels obtained during the demonstration, and their comparison with the results based on channels simulated by a novel geometric optics based channel model suitable for MU-MIMO-OFDM in rural areas. Despite its simplicity, the model was found to predict channel capacity and bit error rate probability accurately for a typical MU-MIMO- OFDM deployment scenario.

Dynamic range analysis on MIMO-OFDM channels in a populated time-varying indoor environment

We investigate the variations on channel capacity for a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system due to the presence of pedestrians. Capacity dynamic range is measured for 2 times 2, 3 times 3, and 4 times 4 antenna configurations in line-of-sight (LoS) and non-LoS (NLoS) environments using fixed signal-to-noise ratio (SNR) and fixed transmitted (Tx) power. It was found that the fixed SNR capacity increased while fixed Tx power capacity decreased in both environments in the presence of pedestrians. The results show larger dynamic range values for LoS over NLoS and similar dynamic range values for different antenna configurations.

Characterisation of body-shadowing effects in the indoor environment at 5.2 GHz

Human body shadowing effects can considerably influence the channel characteristics of indoor radio communication systems. In this work, body-shadowing effects were measured for a line-of-sight (LOS) point-to-point 5.2 GHz link with up to 3 pedestrians moving within a 42 m/sup 2/ room. The results show that received power values are significantly dependent on whether or not the users body obstructed the direct ray to the transmitter. Under obstructed conditions, the measured body shadowing effect was an attenuation of up to 10 dB. The first order statistics for the experimental scenarios tend to be Rice distributed with the K factor decreasing as the number of pedestrians present increased.

Empirical vehicle-to-vehicle pathloss modeling in highway, suburban and urban environments at 5.8 GHz

In this paper, we present a pathloss characterization for vehicle-to-vehicle (V2V) communications based on empirical data collected from extensive measurement campaign performed under line-of-sight (LOS), non-line-of-sight (NLOS) and varying traffic densities. The experiment was conducted in three different V2V propagation environments: highway, suburban and urban at 5.8GHz. We developed pathloss models for each of the three different V2V environments considered. Based on a log-distance power law model, the values for the pathloss exponent and the standard deviation of shadowing were reported. The average pathloss exponent ranges from 1.77 for highway, 1.68 for the urban to 1.53 for the suburban environment. The reported results can contribute to vehicular network (VANET) simulators and can be used by system designers to develop, evaluate and validate new protocols and system designs under realistic propagation conditions.

Deterministic diffraction loss modelling for novel broadband communication in rural environments

This paper presents a deterministic modelling approach to predict diffraction loss for an innovative Multi-User-Single-Antenna (MUSA) MIMO technology, proposed for rural Australian environments. In order to calculate diffraction loss, six receivers have been considered around an access point in a selected rural environment. Generated terrain profiles for six receivers are presented in this paper. Simulation results using classical diffraction models and diffraction theory are also presented by accounting the rural Australian terrain data. Results show that in an area of 900 m by 900 m surrounding the receivers, path loss due to diffraction can range between 5 dB and 35 dB. Diffraction loss maps can contribute to determine the optimal location for receivers of MUSA-MIMO systems in rural areas.

Effects of user distribution on multiuser MIMO-OFDM channel capacity in rural area

Multi-user multiple-input multiple-output orthogonal frequency division multiplexing (MU-MIMO-OFDM) is a promising technology to improve the spectrum efficiency of fixed wireless broadband access systems in rural areas. When MU-MIMO is deployed in predominantly line-of-sight (LoS) environments, for instance in rural areas, the problem of ill-conditioned channels may occur. This letter investigates the effects of capacity degradation with user distribution angle from 10° to full azimuthal angle, based on the results of a deterministic model. The deterministic model developed for rural MU-MIMO-OFDM has been validated with the experimental data. Furthermore, the validated deterministic model has been used to study the optimal distribution of users in a rural MU-MIMO-OFDM system. The optimum capacity has been observed for a user distribution with an angle between 180° and 360° around the access point.

Experimental Evaluation of DCOOP Protocol Using USRP-RIO Based Testbed at 5.8GHz

Cooperative communication can attain lower error probability in wireless networks by exploiting the inherent broadcast nature and taking advantage of multi-path propagation. In order to leverage performance gains achieved by virtual multiple- input multiple-output (MIMO) systems, we design a novel cooperative protocol, Decode-to-Cooperate (DCOOP). We evaluate its performance on a testbed implemented on Universal Software Radio Peripheral Reconfigurable Input/Output (USRPRIO) platform. The main challenge during the testbed deployment was to consider transmission under tightly synchronized nodes in a slow fading environment. Extensive experiments were performed to evaluate the performance of the testbed and the results show that it can operate at lower transmit power and increase the coverage area for a desired bit error rate (BER).

Doppler and pathloss characterization for vehicle-to-vehicle communications at 5.8 GHz

Due to significant increase in vehicular accident and traffic congestions, vehicle to vehicle (V2V) communication based on the intelligent transport system (ITS) was introduced aiming to significantly reduce vehicular accident and traffic congestion. However, to carry out efficient design and implementation of a reliable vehicular communication systems, a deep knowledge of the propagation channel characteristics in different environments is crucial, in particular the Doppler and pathloss parameters. This paper presents an empirical V2V channel characterization and measurement performed under realistic urban, suburban and highway driving conditions in Brisbane, Australia. Based on Lin Cheng statistical Doppler Model (LCDM), values for the RMS Doppler spread and coherence time due to time selective nature of V2V channels are presented. Also, based on log-distance power law model, values for the mean pathloss exponent and the standard deviation of shadowing were reported for urban, suburban and highway environments. The V2V channel parameters can be useful to system designers for the purpose of evaluating, simulating and developing new protocols and systems.

Adaptive subcarrier allocation in multiuser OFDM system using forced cost based decisions

Subcarrier allocation scheme for Orthogonal Frequency Division Multiplexing(OFDM) based multiuser system is proposed. Most previous algorithms use greedy approach as a subcarrier allocation scheme until a conflict occurs or as an initial first round allocation with improvement steps carried out in next rounds. Our algorithm uses information obtained by the forced costs of a system that incur by a current allocation to make assignment decisions. This algorithm does not rely on greedy approach and therefore can also be considered as a substitute for first layer Greedy algorithms. Simulation results show that for two user case this algorithm gives better or equal allocation 80-90 percent of the time when compared with the greedy allocation.