台北都會區GSM/3G行動通信頻譜使用率量測與分析

Abstract

近年來，因行動通訊服務需求遽增，現有固定頻譜分配政策已窘迫不合用。美國聯邦通信委員會(FCC)調查報告顯示時段與地理上差異可造成頻譜使用率15％至85%有大幅不同。一種可動態地找出可供使用的頻帶，進而提升頻寬的使用效率的新興技術「動態頻譜接取(Dynamic Spectrum Access, DSA)」的構想乃因應而生。 本論文的主要研究目的是評估台北都會區GSM/3G無線電頻譜是否存有機會可供已DSA技術進行彈性化頻譜共享使用。研究重點專注於探討目前台北都會區潛在的次級頻譜市場可用頻譜，評估未來新興無線/行動通信頻譜服務與應用需求趨勢。結合以上二者在頻譜的供需關係，達成初探台北都會區是否有動態頻譜接取空間的目的。 本論文使用頻譜分析儀、全向性天線組成量測硬體設備。為了進行頻譜使用率量測，我們並設計頻譜使用率量測環境與方法。頻譜使用率量測實驗獨立變數包括(1)頻譜(依我國未來頻譜重新分配政策方針來選擇)、(2)地點(依使用者需求特性來選擇)、(3)時間(依頻譜使用頻繁程度來選擇)，所量測的指標包括頻譜使用率、頻譜空檔時間分佈；所得數據以Matlab分析軟體進行功率臨界值準則比較與分析，探討下列議題:1.頻譜使用率與GSM/3G頻譜的對應關係,2.頻譜使用率與地點的對應關係,3.頻譜使用率與時間的對應關係,4.頻譜空檔時間分布與GSM/3G頻譜的對應關係,5.頻譜空檔時間分布與地點的對應關係,6.頻譜空檔分布與時間的對應關係。另外，為了充分掌握一天之中所有時段頻譜使用率的變化，我們採用每32秒取樣一次，共取樣2700次的24小時不間斷量測。 本論文實驗量測結果: (1) 3G在不同地點整體頻帶使用率介於20%~45%，以MRT地點的頻譜使用率為最高(44%)；(2) 3G在不同時間頻譜使用率變化不大；(3) 3G在不同頻帶頻譜使用率有下行頻帶使用率明顯高於上行頻帶使用率的現象；(4) GSM在不同地點整體頻帶使用率介於50%~90%之間，除了台大學術單位地點頻譜使用率較為偏低；(5)GSM在不同時段，使用率有離峰時段的13.3%到尖峰時段的90%大幅的變化。(6) GSM在不同頻帶使用率，呈現下行頻帶使用多於上行頻帶的非對稱性現象；(7) 3G/GSM在尖峰時段/離峰時段一小時內，分別有最短時間為16秒到長達57分鐘的頻譜空檔時間，可提供通信服務使用；(8)在頻帶供給方面，3G頻譜(150MHz)比GSM(16MHz)有較多的頻帶可供其他業務頻譜技術使用。 由以上分析，可發現無論在頻帶、地點或時間上，GSM頻譜使用率皆有高於3G頻譜使用率的現象，由此現象看來，使用者普遍還是習慣使用2G技術來進行無線通信服務。而導致3G頻譜使用率不彰，造成無線頻譜資源未充分利用。 另一方面，未來無線行動通信頻譜的服務需求將朝向寬頻化、移動高速化、多種接取技術多元整合化方向增加(如:WiFi+WiMAX，WiFi+WiMAX+3G，GSM+3G..)的趨勢。 綜合以上分析與探討，無論在時間、地點，3G頻帶均至少有70MHz的頻寬可供利用，無疑對未來寬頻化的無線行動通信需求是一大福音；而現有GSM頻譜的已提供不錯的頻譜使用率(50%~90%)，但仍未達百分百利用，或許可效法歐洲允許運營商在900MHz頻段發展3G業務，將部分現有3G業務轉移到GSM頻帶發展，一方面可補足目前現有的GSM頻譜空洞，使得頻譜使用率更加提升，另一方面也將空出更多的3G頻帶，供未來寬頻化及多元化接取技術等需求分配使用，整合以上討論，本論文亦更加肯定台北都會區有彈性化頻譜共享的空間。

In recent years, because the demand for mobile communication service has increased rapidly,the existing fixed frequency spectrum distribution policy is not appropriate anymore. According to the U.S. FCC survey report [FCC03], the spectrum utilization has huge variation from 15% to 85% due to different time slots and geographic locations.The inefficiency could be solved by the support of “Dynamic Spectrum Access” which offers the potential to adapt to traffic dynamics and utilize spectrum efficiently [FCC03]. The main purpose of the thesis is to assess whether there’s an opportunity for the GSM/3G spectrum to be utilized by DSA in metropolitan Taipei.The research first puts emphasis on discussing the potential secondary spectrum market’s available spectrum.Furthermore,it will evaluate trends of future emerging mobile/wireless communication spectrum services and applications.With the discussion of the relationship between the demand and supply of the frequency spectrum,we can achieve the goal of studying whether there’s room for dynamic spectrum access in metropolitan Taipei. In this thesis,the hardware devices comprise spectrum analyzer and omni-directional antenna.In order to measure the spectrum utilization,we designed a set of methods for spectrum utilization measurement and created an environment for it.The experiment variables include:(1)spectrum band (based on Taiwan’s future policy of spectrum redistribution.(2)location (based on the users demands).(3)time (based on the frequency of spectrum use). Measurement index includes spectrum utilization and spectrum idle duration distribution；The resulting data will be compared with the power threshold value by using the Matlab analysis software to discuss the following issues:(1)The relationship between spectrum utilization and GSM/3G bands；(2)The relationship between spectrum utilization and locations；(3)The relationship between spectrum utilization and times；(4)The relationship between spectrum idle duration distribution and GSM/3G bands；(5)The relationship between spectrum idle duration distribution and locations；(6)The relationship between spectrum idle duration distribution and time.Moreover,in order to be in control of spectrum utilization change in all time intervals during one day, we set each sampling period for 32 seconds, which means 2,700 periods in total within one day and measured uninterruptedly. The results of the experiment are as follows:(1)The average spectrum utilization of 3G is between 20% to 45% in four different locations,with the highest spectrum utilization taking place in MRT(44%).(2)Spectrum utilization of 3G has subtle change at different time.(3)In terms of spectrum utilization of 3G,the downlink is perspicuously higher than the uplinkin different band.(4)Spectrum utilization of GSM is between 50% to 90% on average in the different locations,with the lowest taking place in NTU(60%).(5) Spectrum utilization of GSM changes from the offpeak time interval utilization(13.3%) to the peak time interval utilization(90%) in the different time intervals.(6)GSM has asymmetric traffic between uplink and downlink in different band.(7)There’s a spectrum interval of 16 seconds at least to 57 minutes at most that’s available for communication service within offpeak and peak.(8)In terms of spectrum supply,3G spectrum(150MHz) has more bands for other spectrum technology to use than GSM(16MHz). Based on the above analysis,we can find that GSM spectrum is used more frequently than 3G spectrum in terms of band, location and time.It seems that mobile users are used to 2G technology for wireless communication, which causes 3G wireless mobile spectrum underutilized.On the other hand,the future demand of wireless mobile communication will be broadband oriented, high-speed oriented and multi-access oriented(EX:WiFi+WiMAX,WiFi+WiMAX+3G,GSM+3G..etc.). In summary,3G bands have at least 70Mhz of available bandwidth at any time and location,which no doubt is a good news to wireless mobile communications since spectrums supplies are getting short.Though present GSM spectrum band has fine spectrum utilization (50% ~ 90%),there is still a small gap to fully utilization.To solve this problem,we can follow the Europeans who allow 3G services development in the 900MHz band while transferring part of the 3G business to GSM bands.On one hand, it can complement the existing GSM spectrum hole, making higher utilization of the spectrum; on the other hand it will provide more 3G bandwidth for broadband access and diversity technology use in the future.All in all, we believe that there is room for the development and application of dynamic spectrum access technology in metropolitan Taipei.