2、 蜂窩系統(tǒng)概述
2、Overview of Cellular Systems

This book is concentrated around the topic of indoor radio planning from a practical perspective, and it is not the within the scope of this book to cover the full and deep details of the GSM and UMTS systems and structures. This book will only present the most important aspects of the network structure, architecture and system components, in order to provide basic knowledge and information that is needed as a basis for design and implementation of indoor coverage and capacity solutions. For more details on cellular systems in general refer to [2].
本書集中于從實踐的角度看室內(nèi)無線規(guī)劃，并不全面、深入的探討GSM和UMTS系統(tǒng)的細(xì)節(jié)和結(jié)構(gòu)。為了提供設(shè)計和實現(xiàn)室內(nèi)覆蓋和容量的解決方案所需要基礎(chǔ)知識和信息，書中僅介紹網(wǎng)絡(luò)結(jié)構(gòu)、體系和系統(tǒng)網(wǎng)元的重要的方面。想要了解關(guān)于蜂窩系統(tǒng)的更多的細(xì)節(jié)，請參考[2]。

2.1、 移動電話
2.1.1、 蜂窩系統(tǒng)
2.1 Mobile Telephony
2.1.1 Cellular Systems

The concept of cellular coverage was initially developed by AT&T/Bell Laboratories. Prior to that, the mobile telephony systems were manual systems used only for mobile voice telephony.Typically implemented with high masts that covered large areas, and with limited capacity per mast, they were only able to service few users at the same time – in some cases even only one call per mast! These systems also lacked the ability to hand over calls between masts, so mobility was limited to the specific coverage area from the servicing antenna, although in reality the coverage area was so large that only rarely would you move between coverage areas. Remember that, at that point, there were no portable mobile telephones, only vehicleinstalled terminals with roof-top antennas. Over time the use of mobile telephony became increasingly popular and the idea was born that the network needed to be divided into more and smaller cells, accommodating more capacity for more users, implementing full mobility for the traffic and enabling the system to hand over traffic between these small cells.
蜂窩覆蓋的概念最初由AT&T/Bell實驗室提出。在此之前，移動電話系統(tǒng)是手動的系統(tǒng)，僅用于移動語音電話。典型的實現(xiàn)是使用很高的發(fā)射天線鐵塔覆蓋廣大的范圍，每個發(fā)射天線的容量有限，只能同時服務(wù)很少的用戶，在一些情況甚至一個發(fā)射塔只能支持一個通話！這些系統(tǒng)還缺乏在不同發(fā)射塔之間切換的能力，因此盡管實際覆蓋范圍很大，但你幾乎不能在覆蓋區(qū)之間移動，移動性被限制在距離天線的特殊的覆蓋范圍內(nèi)。但不要忘了，那時沒有便攜的移動電話，只有在車頂安裝了天線的車載終端。隨著時間的推移，移動電話開始普及，人們也認(rèn)識到網(wǎng)絡(luò)需要分成更多更小的小區(qū)，容納更多的用戶，實現(xiàn)全面的移動性，使系統(tǒng)可以在小區(qū)間切換通話。
From this initial concept several cellular systems were developed over time and in different regions of the world. The first of these cellular systems was analog voice transmission, and some ‘data transmission’ modulated into the voice channel for signaling the occasionally handover or power control command.
隨著時間的推移，在世界的不同地區(qū)從最初的蜂窩概念發(fā)展起來幾種蜂窩系統(tǒng)。其中，第一個蜂窩系統(tǒng)采用模擬語音傳輸，同時一些用于切換或功率控制的信令數(shù)據(jù)被調(diào)制到語音信道上進行“數(shù)據(jù)傳輸”。
Some of the most used standards were/are AMPS, D-AMPS, TACS, PCS, CDMA, NMT,GSM, DCS and UMTS (WCDMA).
應(yīng)用較多的系統(tǒng)有AMPS、D-AMPS、TACS、PCS、CDMA、NMT、GSM、DCS和UMTS（WCDMA）。

AMPS
AMPS (Advanced Mobile Phone System) is the North American standard and operates in the 800 MHz band. The AMPS system was also implemented outside North America in Asia, Russia and South America. This is an analog system using FM transmission in the 824–849 and 869–894 MHz bands. It has 30 kHz radio channel spacing and a total of 832 radio channels with one user per radio channel.
AMPS
AMPS（高級移動電話系統(tǒng)）是北美的標(biāo)準(zhǔn)，工作于800MHz頻段，在亞洲、俄羅斯和南美等地也有部署。這是一個模擬系統(tǒng)，在824–849MHz和869–894MHz采用FM傳輸。系統(tǒng)的無線信道間隔30kHz，共有832個信道，每個無線信道可容納一個用戶。
D-AMPS
D-AMPS (Digital Advanced Mobile Phone System) evolved from AMPS in order to accommodate the increasingly popular AMPS network with fast-growing traffic and capacity constraints. The D-AMPS system used TDMA and thus spectrum efficiency could be improved,and more calls could be serviced in the same spectrum with the same number of base stations.
D-AMPS
D-AMPS（數(shù)字高級移動電話系統(tǒng)）從AMPS演進而來，為了使日益普及的AMPS網(wǎng)絡(luò)可以適應(yīng)快速增長的話務(wù)容量。D-AMPS采用TDMA技術(shù)，因此頻譜效率可以得到提高，即采用同樣的頻譜、同樣多的基站可以支持更多通話。

TACS
TACS (Total Access Cellular System) was also derived from the AMPS technology. The TACS system was implemented in the 800–900MHz band. First implemented in the UK, the system spread toother countries in Europe,China, Singapore,HongKong and the Middle East and Japan.
TACS
TACS（全接入蜂窩系統(tǒng)）也是由AMPS技術(shù)演進而來，工作于800–900MHz。TACS首先部署與英國，后來在歐洲、中國、新加坡、香港、中東和日本都有部署。

PCS
PCS (Personal Communications System) is a general term for several types of systems developed from the first cellular systems.
PCS
PCS（個人通信系統(tǒng)）是第一代蜂窩系統(tǒng)的幾種系統(tǒng)類型的一個通用的術(shù)語

CDMA
CDMA (Code Division Multiple Access) was the first digital standard implemented in the USA. CDMA uses a spread spectrum in the 824–849 and 869–894 MHz bands. There is a channel spacing of 1.23 MHz, and a total of 10 radio channels with 118 users per channel.
CDMA
CDMA（碼分多址）是美國實現(xiàn)的第一個數(shù)字標(biāo)準(zhǔn)。CDMA使用824–849和869–894 MHz擴展頻譜，信道間隔1.23MHz，共有10個無線信道，每個信道容納118個用戶。

NMT
NMT (Nordic Mobile Telephony) was the standard developed by the Scandinavian countries, Denmark, Norway and Sweden, in 1981. Initially NMT was launched on 450MHz, giving good penetration into the large forests of Sweden and Norway, and later also deployed in the 900MHz band (the band that today is used for GSM). Being one of the first fully automatic cellular systems in the world (it also had international roaming), the NMT standard spread to other countries in Europe, Asia and Australia.
NMT
NMT（北歐移動電話）是由包括丹麥、挪威和瑞典在內(nèi)的北歐國家在1981年發(fā)展的標(biāo)準(zhǔn)。起初，NMT工作于450MHz，可以在瑞典和挪威的大面積森林地區(qū)獲得好的穿透損耗，后來它也工作于900MHz（現(xiàn)在該頻段用于GSM系統(tǒng)）。作為世界上首批全自動蜂窩系統(tǒng)之一（它也可以實現(xiàn)國家間漫游），NMT系統(tǒng)在歐洲、亞洲和澳大利亞等國家也有應(yīng)用。
GSM
GSM (Global System for Mobile communication) was launched in the early 1990s, and was one of the first truly digital systems for mobile telephony. It was specified by ETSI and originally intended to be used only in the European countries. However GSM proved to be a very attractive technology for mobile communications and, since the launce in Europe, GSM has evolved to more or less a global standard.
GSM
GSM（全球移動通信系統(tǒng)）開始于1990s早期，是首批真正的數(shù)字移動電話系統(tǒng)之一。它由ETSI規(guī)范，最初只想在歐洲國家部署。但事實證明GSM是一種非常有吸引力的移動通信技術(shù)，自從在歐洲開始使用，GSM多少已發(fā)展為一種國際標(biāo)準(zhǔn)。
DCS
Originally GSM was specified as a 900 MHz system, and since then the same radio structure and signaling system have been used for DCS1800 (Digital Cellular Telecommunication System). The GSM basic has also been applied to various spectra around 800–900 and 1800–1900 MHz across the world, the only difference being the frequencies.
DCS
GSM最初應(yīng)用于900MHz，后來同樣的無線結(jié)構(gòu)和信令系統(tǒng)用于DCS1800（數(shù)字蜂窩通信系統(tǒng)）。GSM系統(tǒng)在世界上其它國家也被應(yīng)用于800–900 MHz和1800–1900 MHz左右的頻段上，不同的僅僅是頻率。
UMTS (WCDMA)
After the big global success with the second generation (2G) GSM and the increased need for spectrum efficiency and data transmission, it was evident that there was a need for a third-generation mobile system. UMTS was selected as the first 3G system for many reasons, mainly because it is a very efficient way to utilize the radio resources – the RF spectrum. WCDMA has a very good rejection of narrowband interference, is robust against frequency selective fading and offers good multipath resistance due to the use of rake receivers. The handovers in WCDMA are imperceptible due to the use of soft handover, where the mobile is serviced by more cells at the same time, offering macro-diversity.
UMTS (WCDMA)
GSM屬于第二代（2G）移動通信。GSM在全球取得巨大的成功后，高頻譜效率和數(shù)據(jù)傳輸?shù)男枨蟾�加強烈。很明顯，需要第三代移動通信系統(tǒng)。UMTS被作為3G系統(tǒng)的首選有很多原因，主要是由于它可以有效地利用無線資源——無線頻譜。WCDMA可以很好的抗窄帶干擾，抗頻率選擇性衰落。由于使用了Rake接收機，可以提供好的抗多徑能力。在WCDMA中使用了軟切換，因此感覺不到切換過程。在軟切換時，一個手機可以同時與多個小區(qū)相連，因此可以提供宏分集功能。
However there are challenges when all cells in the network are using the same frequency. UMTS is all about noise and power control. Strict power control is a necessity to make sure that transmitted signals are kept to a level that insures they all reach the base station at the same power level. You need to minimize the inter-cell interference since all cells are operating on the same frequency; this is a challenge.
但是，當(dāng)網(wǎng)絡(luò)中所有小區(qū)都使用相同的頻率時也面臨著很多挑戰(zhàn)。UMTS很多工作都與噪聲和功率控制有關(guān)。必須通過嚴(yán)格的功率控制確保到達基站的發(fā)射功率基本相同。另外，既然所有小區(qū)使用相同頻率，還需要使小區(qū)間的干擾盡可能小。
Even though soft handovers insure that the mobile can communicate with two or more cells operating on the same frequency, one must remember that the same call will take up resources on all the cells the mobile is in soft handover with. The handover zones need to be minimized to well-defined small areas, or the soft HO can cannibalize the capacity in the network.
軟切換雖然使手機可以與兩個或更多個使用同一頻率的小區(qū)進行通信，但同樣的呼叫將占用所有處于軟切換狀態(tài)下的小區(qū)的資源。切換區(qū)域需要很好的定義并盡量小，否則軟切換將占用網(wǎng)絡(luò)的容量。
UMTS has now become the global standard and has been accepted throughout the world. Several upgrades that can accommodate higher data speed HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Data Access) can service the users with data speeds in excess of 10 Mbps.
UMTS現(xiàn)在已成為國際標(biāo)準(zhǔn)并被世界所接受。HSDPA（高速下行分組接入）和HSUPA（高速上行數(shù)據(jù)接入）作為UMTS的升級版本，能夠為用戶提供超過10Mbps的數(shù)據(jù)速率。
There are several current considerations about converting the current GSM900 spectrum into UMTS900, giving a much higher spectrum efficiency, and better indoor RF penetration.
現(xiàn)在有考慮將GSM900的頻段用于UMTS900，以期獲得更高的頻譜效率和更好的室內(nèi)射頻穿透能力。

2.1.2、 無線傳輸概述
2.1.2 Radio Transmission in General
Several challenges need to be addressed when using radio transmission to provide a stable link between the network and the mobile station. These radio challenges are focused around the nature of the propagation of radio waves and especially challenges of penetrating the radio service into buildings where most users are located these days.
在網(wǎng)絡(luò)和移動臺之間提供穩(wěn)定的鏈路需要解決幾個問題。這些問題集中于無線電波的傳播特性，尤其是在建筑物內(nèi)無線穿透特性，因為現(xiàn)在大部分用戶都在室內(nèi)。
The challenges are mainly radio fading, noise control, interference and signal quality. These challenges will be addressed throughout this book, with guidelines on how to design a high-performing indoor radio service.
主要的問題是無線衰落、噪聲控制、干擾和信號質(zhì)量。本書將討論這些問題，并就如何設(shè)計高性能的室內(nèi)無線業(yè)務(wù)給出指導(dǎo)。

2.1.3 The Cellular Concept
After the initial success with the first mobile system, it was evident that more capacity needed to be added to future mobile telephony systems. In order to implement more capacity to accommodate more users in the increasingly more popular mobile telephony systems, new principles needed to be applied. The new concept was to divide the radio access network into overlapping ‘cells’, and to introduce a handover functionality that could insure full mobility throughout the network, turning several masts into one coherent service for the users.
2.1.3、 蜂窩的概念
第一代移動系統(tǒng)取得成功后，新的移動電話系統(tǒng)需要更多的容量。為了使不斷普及的移動電話系統(tǒng)提供更多的容量，容納更多的用戶，系統(tǒng)采用了新的原理。無線網(wǎng)絡(luò)被分成很多交疊的“小區(qū)”，并且引入切換功能確保在全網(wǎng)的移動性以及將分散的發(fā)射天線塔整合成一個連續(xù)的服務(wù)區(qū)。
Dividing the network into cells has several advantages and challenges. The advantages are:
將網(wǎng)絡(luò)劃分成很多小區(qū)既有優(yōu)點也面臨著一些挑戰(zhàn)。優(yōu)點包括：
Frequency reuse – by planning the radio network with relative low masts with limited coverage area, compared with the first mobile systems, you could design a radio network where the cells will not interfere with each other. Then it is possible to deploy the same radio channel in several cells throughout the network, and at the same time increase the spectrum and radio network efficiency thanks to frequency reuse.
頻率復(fù)用——與第一代移動通信系統(tǒng)相比，通過降低發(fā)射塔來限制覆蓋區(qū)域，可以設(shè)計一個沒有小區(qū)干擾的無線網(wǎng)絡(luò)。這樣就可以在全網(wǎng)的不同小區(qū)部署相同無線信道。因此，通過頻率復(fù)用可以提高頻譜和無線網(wǎng)絡(luò)的效率。
Capacity growth – the cellular network could start with only a few cells, and as the need for better coverage and more capacity grew, these large cells could be split into smaller cells, increasing the radio network capacity even more with tighter reuse of the frequencies (as shown in Figure 2.1).
容量提升——蜂窩網(wǎng)絡(luò)在開始時可以只用少量的小區(qū)。隨著覆蓋和容量需求的增長，大的小區(qū)可以進一步分成小的小區(qū)，通過緊密地頻率復(fù)用更多地提升無線網(wǎng)絡(luò)容量。（如圖2.1）

Figure 2.1 The cell structure of a cellular radio network. Cells will be split into smaller cells as the network evolves, and the capacity need grows
圖 2 1 蜂窩無線網(wǎng)絡(luò)的小區(qū)結(jié)構(gòu)。隨著網(wǎng)絡(luò)發(fā)展和容量需求增加，小區(qū)進一步被分成更小的小區(qū)

Mobility – it is paramount for cellular networks that handovers are possible between the cells, so the users can roam through the network with ongoing connections and no dropped calls. With the advent of the first cellular systems, mobile users could now move around the network, utilizing all the cells as one big service area.
移動性——對蜂窩網(wǎng)絡(luò)最重要的是在小區(qū)間可以切換。這樣，用戶就可以在通話過程中在網(wǎng)絡(luò)中漫游而不會掉話。隨著第一代蜂窩系統(tǒng)的出現(xiàn)，移動用戶可以在整個網(wǎng)絡(luò)中移動，使用網(wǎng)絡(luò)中所有的小區(qū)，就好像在一個大的服務(wù)區(qū)。

The challenges are:
面臨的挑戰(zhàn)有：
Network structure – when deploying the cellular structure one needs to design a theoretical hexagonal roll-out, by deploying omni, three-sector or six-sector base stations, and make sure the cells only cover the intended area. It is important that the cells only cover the intended area, and that there are no ‘spill’ of radio coverage to the coverage area of other cells in the network.
網(wǎng)絡(luò)結(jié)構(gòu)——在部署網(wǎng)絡(luò)結(jié)構(gòu)是，人們需要用全向站、三扇區(qū)站或六扇區(qū)的基站構(gòu)造一個由理想的六邊形的組成的網(wǎng)絡(luò)，并且確保每個小區(qū)覆蓋設(shè)定的區(qū)域。每個小區(qū)只覆蓋設(shè)定的區(qū)域，而不會對使信號泄漏到網(wǎng)絡(luò)中其它小區(qū)的覆蓋區(qū)域，這一點很重要。


待續(xù)……

[[i] 本帖最后由 qingren 于 2009-6-26 16:01 編輯 [/i]]