Measurement and Analysis of Spectrum Utilization and Coveragefor 3G/WiFi: NTU Campus Study
Date Issued
2013
Date
2013
Author(s)
Shih, Yu-Hung
Abstract
User demands for broadband mobile data access via the third generation (3G) mobile communication systems have constantly risen in recent years, and the total 3G phone numbers has grown to 23 million and up. Taiwan''s major telecommunication companies have been facing the challenge of increasing deployment of base stations for good signal coverage and throughput. To overcome the poor signal coverage caused by blockage of buildings or long distance from accessible base stations, short distance transmission-based WiFi hotspots have been widely deployed as a complimentary solution to offload 3G access traffic. For example, there have been over 4,000 WiFi hotspots in Taipei city as of 2012.
It is well known that dense deployment of WiFi hotspots does not necessarily lead to good coverage and effective spectrum utilization without proper design of hotspot locations and channel interference avoidance. Signal coverage and spectrum utilization may largely vary with communication environments and locations of base stations and hotspots. Therefore, direct measurements provide, from consumers’ point of view, understanding of spectrum utilization and signal coverage in an area.
This thesis conducts measurement research over National Taiwan University campus. Research objectives are as follows:
1. To study in theory how spectrum utilization varies with different access technologies and how signals of different frequencies are attenuated with environment so that the measurement techniques adopted truly capture the effect of access technologies on wireless signals;
2. To conduct measurements and estimation of 3G and WiFi spectrum utilization and signal coverage over National Taiwan University campus
2.1) to investigate the definition of spectrum utilization by data access and the actual utilization, and
2.2) to conduct evaluation of the effect of indoor and outdoor environment factors on WiFi signal coverage, the joint coverage between 3G and WiFi and correlation analysis between the two usage modes.
The measurement system of spectrum utilization consists of a spectrum analyzer, an omni-antenna, a PC and a MatlabTM based analyzer. The measurement research first addresses the deficiencies of in defining 3G spectrum utilization by the existing literature, studies via measurements how the number of users and measurement locations affect 3G spectrum utilization, and defines the downlink frequency band utilization as spectrum utilization indicator. This thesis (1) recommends that the measured code powers under different number of users in a single channel be used to identify the impact of user number on spectrum utilization and (2) explains why the use of downlink spectrum utilization as an indicator may reduce measurement error. This thesis also performs and analyzes measurements of WiFi spectrum utilization over the three dimensions of channel, time, and location. In measuring signal coverage, this thesis focuses on the distribution of indoor and outdoor signal power level. The measurement system consists of a spectrum analyzer and smart mobile phones equipped with APP software “WiFi-Analyzer” as hardware measurement devices. The independent variables of indoor WiFi signal measurement include channel and location. Collected data is used to estimate the signals at the unmeasured location by application of the Ordinary Kriging method, and then validated by further measurements. Items of analyses are (3) the relationship between the known WiFi hotspots and the average power level, (4) the relationship between the self-configured WiFi hotspots and the average power level, (5) the impact of WiFi signals dispersed between floors on the average power. The issues of outdoor WiFi/3G signal coverage measurement include (6) the relationship between the indoor and outdoor WiFi signals, (7) the relationship between the surroundings (department building, open space, etc.) and the 3G average power level, (8) relationship between the surroundings and the average WiFi power level, and (9) comparison between the 3G signal and the average WiFi signal power levels.
The measurement results of spectrum utilization show that in an environment of dense WiFi hotspot configuration, most users will choose to use WiFi for data access service. For example, the difference between the changes in spectrum utilization at different locations over National Taiwan University campus may reach up to 50%, wherein the spectrum utilization changes from the off-peak time interval utilization to the peak-time interval utilization reaches about 30%. Therefore, with the rising demand for mobile broadband access, the opportunities for 3G data access may increase by providing WiFi AP widely and improving the spectrum utilization of the ISM band. From the viewpoint of signal coverage, the power level of outdoor 3G signal outdoor coverage is distributed approximately in -64~-84 dBm, which is much higher than outdoor WiFi signal of only up to -84 dBm. It can be inferred that in the outdoor environment, most users would take 3G access as a priority.
Subjects
無線數據頻譜
頻譜使用率量測
WiFi
3G
訊號涵蓋範圍量測
Type
thesis
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