微細胞行動通信系統之中斷率分析與涵蓋區預測

Abstract

頻率複用(frequency reuse)是蜂巢式通信系統擴充系統容量及提高頻譜 使用效率的核心觀念。然而在頻率重複使用的情形下，基地台的涵蓋區( coverage area)除受限於發射功率之外，亦受同頻干擾之限制。本論文旨 在分析微細胞行動通信系統在干擾環境中的中斷率(outage probability) ，並將之應用於頻率複用距離}(reuse distance)的預估以及基地台的涵 蓋區預測。就類比系統而言，當接收信號之載波干擾比(carrier-to- interference ratio)與載波雜訊比(carrier-to-noise ratio)未符合某 一特定規格時，則此通訊鏈路中斷(outage)。若是數位系統，其中斷之發 生則應以位元錯誤率(bit error rate)為判斷標準。本文所考慮的是一設 置於都會街區中的微細胞系統，在此環境中，假設信號是通過一萊斯衰褪 通道(Rician fading channel)，並且受到同頻道信號之干擾(co-channel interference)。對於類比式系統，我們推導出在此通訊環境中的中斷率 數學式，並且探討信號遮蔽(shadowing)效應的影響。同時，在位元錯誤 率的標準下，我們對微細胞環境中的數位式GMSK系統作一分析。利用所得 的結果，可以有效地估計適當的頻率複用距離、預測基地台的涵蓋區，並 可進一步用來決定頻率複用型式(reuse pattern)及基地台設置的最佳位 置。 To accommodates more users per unit area, a cellular mobile radio systemdeliberately reuses radio channels over relative short distances. However, thereception quality may deteriorate because of the presence of cochannel interference(CCI). The service quality of a radio communicationsystem is often measured by outage probability defined as the probability of failingto meet a certain system performance requirement. The service area of a base stationin turn is defined as the area within which the outage probability is less thany percent.For analog systems the performance requirement is specified by the minimum carrier-to- noiseratio (CNR) or the carrier-to-interference ratio (CIR) or both. For digital systems thecorresponding performance measure is the bit error probability.This first part of this thesis presents outage probability analysis for microcellular mobile radiosystems that operate in a Rician (desired signal) / Nakagami (undesiredsignal) fading environment.The interferers may have identical or different statistics. The effect of log- normalshadowing on the outage probability are investigated as well.The second part of the thesis deals with outages in a GMSK system employing differentialdetection. The communication environment considered is a frequency-selective Rician fadingchannel. We find that in most cases of interest the BER requirement is equivalent tothe CIR and CNR requirements. The last part applies the outage analysis results to studythe influence of the system's CIR requirements on the reuse distance and theservice area prediction, both are useful information for cell planning.