Study Of Propagation Characteristics For Indoor Short-range Wireless Channel

The propagation characteristics of radio channel are the key factors for improving thecommunication quality and reducing the system costs. As the application of wireless sensor networkdevelops rapidly, and the fourth generation mobile communication system is beginning commercialoperation gradually, the indoor short-range wireless communication will be widely used in mostfields with promising prospects. Under indoor short-range environment, due to the effects of indoorscenarios, frequency band, persons and so on, the interior electromagnetic fields become more andmore complex, therefore it is necessary to further research propagation characteristics of radiochannel. The measurements are conducted under office and stairwell scenarios at5.8GHz and2.6GHz frequency band for both Single-Input Single-Output (SISO) and Multiple-InputMultiple-Output (MIMO) systems. Based on the measured data, the propagation characteristics ofpath loss, multipath propagation, cross polarization discrimination (XPD) are analyzed, aiming todraw up empirical statistical models with environment, frequency, persons and so on. The mainachievements are as follows:Firstly, the measured technology of wireless channel in time domain and frequency domain areanalyzed in detailed. Comparing with the measured system in time domain, the equipments formeasurements in frequency domain are simple and the measuring time is short. In indoorshort-range environment, the receiver could synchronize with transmitter precisely, so it choosesfrequency sweep method to research the propagation characteristics. Combining with the existingexperimental equipments, the SISO and MIMO measurement systems are set up, respectively.Then, the SISO measurement scheme is designed in some rooms at4.3-7.3GHz band (centeredat5.8GHz) under indoor short-range environment to research the path loss. Based on theexperimental datum sampled in both line of sight (LOS) and non-LOS (NLOS) conditions, first thepower function by using least square method is used to fit path loss exponent n and frequency f.Then the probability statistical characteristics of n and shadow fading X are studied. Next a novelempirical path loss model is established in frequency and space domain with frequency and distance.It shows that higher frequency leads to smaller n, and the standard deviation of both n and shadowfading X are modeled as frequency-dependent Gaussian variables.Next, the person density under indoor short-range environment is counted to define theoff-hour scenario and rush-hour scenario. Based on the measurements in off-hour and rush-hour at 2.6GHz band, the propagation characteristics, especially the multipath propagation characteristicswith persons are researched. It is studied that the additional path loss caused by the persons in theroom is accounted for with the linear term δ·d. The root mean square (RMS) delay spread is inverseto3-dB coherence bandwidth fitting by an exponential expression. Statistical values show that themedian value of RMS delay spread for rush-hour has an increasing than that for off-hour. It is also foundthat a normal distribution fits the statistical distribution of3-dB coherence bandwidth well inoff-hour while a t-location distribution fits appropriately in rush-hour. Particularly in NLOS conditionrush-hour scenario, the multipath components can’t be obviously distinguished in several clustersand the optimized-fit distributions for multipath magnitude and number of multipath yield toNakagami-m distribution and t-location-scale distribution, respectively.Finally, under the the stairwell environment the2x2MIMO channel measurements at2.6GHzfrequency band are conducted for the first time. The research shows that path loss is not increasingwith the distance between transmitting antenna and receiving antenna under NLOS conditionstairwell environment. Thus the path loss model is modeled by defining the path loss variablesdepending on the stairwell steps and the stairwell platform. The measured MIMO channel capacityis close to the capacity of ideal independent and identically distributed Rayleigh fading channel, andthe distribution of the measured eigenvalues matches well with the Nakagami distribution. Then,with hybrid polarized antenna configuration, some MIMO measurements have been conductedunder LOS condition in some offices to study the cross polarization discrimination (XPD). Basedon the large amounts of measurement data, the XPD-frequency exponent NXPDis fitted by distancewith single slope liner function, and an empirical XPD model is established in frequency and spacedomain. The results study that XPD increases with frequency slightly and decreases with distanceslowly, together the standard deviation of NXPDand XPDShadowfollow Nakagami distribution.These researches provide a solid foundation for indoor short-range wireless communicationsystem designing, such as power control, node locating, spectrum utilizing and so on.