移动通信系统：从2G到3G的演变——GSM与cdmaOne

需积分: 9 180 浏览量更新于2024-08-01 收藏 8.26MB PDF 举报

"GSM, cdmaOne and 3G Systems" 本书主要关注全球第二代（2G）移动通信系统——全球系统移动通信（GSM）和cdmaOne的描述和分析。同时，书中还探讨了这两个系统如何演进成为支持多媒体移动通信的第三代（3G）系统。作者在撰写本书时的初衷是对比GSM和当时被称为IS-95的cdmaOne的容量。GSM采用的是时分多址（TDMA）技术，这与第一代（1G）模拟系统使用的频分多址（FDMA）相比是一次显著的技术转变。而IS-95则采用了更复杂的无线接口，即码分多址（CDMA）。当时，工程师们对多种接入方法有着强烈的、有时不太妥协的观点。尽管从频谱效率角度看，作者更倾向于CDMA，但这并不意味着CDMA应该优于TDMA，因为选择系统类型时需要考虑许多复杂的性能和经济因素。 GSM在cdmaOne之前部署，并在全球许多地区占据市场主导地位。它的成功得益于多个因素：先进的核心网络、引入了将手机与用户解耦的subscriber identity modules（SIM卡）、良好的安全系统、由于开放（公共）接口导致的低成本设备、以及与基础GSM系统相比，通过不懈的演进计划实现了显著的频谱效率提升等。 cdmaOne最初是一个无线接口。在当时很少有人认为CDMA可以在蜂窝环境中有效工作的情况下，采用CDMA是一项大胆的举措。但它成功了，建立起了必要的核心网络，并成为了一个全球标准，对GSM构成了激烈的竞争。值得一提的是，欧洲——设计并推广了GSM的地区——选择了宽频带CDMA作为其3G网络的标准。本书的核心目标是向读者提供GSM、cdmaOne和3G系统的详细描述，帮助读者理解这些系统的技术原理、优缺点以及它们如何演进到下一代通信技术。书中涵盖了各种关键技术，包括TDMA和CDMA的工作原理，以及它们在不同环境下的性能表现。此外，书中还可能讨论3G系统的设计目标，如更高的数据传输速率、更好的服务质量（QoS）和更大的网络容量，这些都是为了满足多媒体通信的需求。通过对这些系统深入的分析，读者可以更好地了解移动通信领域的历史发展、技术进步和未来趋势。无论是对通信工程的学生、研究人员还是从业人员，本书都提供了宝贵的参考资料，有助于他们理解2G和3G系统的本质，并为3G及后续技术的发展奠定基础。

1.2. MULTIPLE CELLS

no longer able to receive signals of an acceptable quality from the BS. The point in space at

which this threshold occurs represents a boundary point for the down-link or forward link,

i.e. the transmissions from the BS to the MS.

What about the up-link or reverse link, i.e. the transmission from the MS to the BS?

The two links are never the same. They are similar in GSM and radically different in

cdmaOne. The MS transmitter operates at signiﬁcantly lower power levels than the BS and

so the maximum radiated power levels are lower than those at the BS. The BS is able to

compensate for the MS deﬁciencies by being able to operate at a lower receiver sensitivity

and by employing techniques such as space diversity to enhance the received signal from

the MS. It is important to note that the signal characteristics that we have already discussed

in relation to the down-link (i.e. path loss, fast and slow fading, Doppler shift and ISI) will

also be present in the received up-link signal. To simplify our discussion, we will assume

that our boundary point is the same for either link, unless speciﬁcally stated.

If the MS takes a number of different routes away from the BS and on each route notes

the location where the received signal goes below the receiver sensitivity, then by joining up

these location points on a map we will form a contour around the BS. A stylised arbitrary

irregularly shaped contour is shown in Figure 1.3. The area enclosed within the boundary

is called a cell.

1.2 Multiple Cells

The dimensions of a cell are limited by the transmitter and receiver performances, the path

loss, shadow fading and other factors described in the previous section. If we are going to

cover wide areas we will need to tessellate cells, and switch a MS between BSs as it roams

throughout the network. If hundreds or thousands of cells are required, then some cells must

operate with the same carrier frequencies. This phenomenon is called frequency reuse.

Figure 1.3: A single cell.

CHAPTER 1. INTRODUCTION TO CELLULAR RADIO

Let us consider the situation where each radio carrier supports N trafﬁc channels, and

the spacing between adjacent carriers is B

Hz. Consequently, a trafﬁc channel occupies an

equivalent bandwidth of B

N Hz. Suppose the spectrum regulator assignsW Hz for the

up-link transmissions and W Hz for the down-link transmissions. The number of carriers for

each down-link is approximately W

. If we are going to reuse carriers in other cells we

must ensure that each receiver can operate with an SIR that will give a sufﬁciently low BER.

Let us for the moment consider that the only form of interference is from either users or BSs

in other cells that are using the same trafﬁc channel as a particular mobile in the zeroth cell,

say. This interference is called co-channel interference or intercellular interference.To

ensure that the interference is sufﬁciently low compared with the required signal power S

(i.e. the SIR is sufﬁciently high) the interfering cells must be spaced sufﬁciently far apart.

This may mean that other cells must be spaced between the zeroth cell and the interfering

cells. Each cell is given a different channel set until all the bandwidth W is used. If this

means M cells consume the bandwidth W,thenwehaveM contiguous cells that form a

cluster of cells. We now form another cluster of M cells and tessellate it with the ﬁrst

cluster. In each cluster all the channels are used, and the clusters are arranged such that two

cells that use the same channel set are spaced as far apart as possible. Figure 1.4 shows two

four-cell clusters where the cells marked A, B, C and D in each cluster, respectively, use the

same channel sets.

The number of cells in the cluster, M, is called the reuse factor. The value of M depends

on the SIR. If, for an acceptable BER, the SIR is required to be high, then we must have

many cells in the cluster in order to space the ‘reuse cells’ sufﬁciently far apart such that the

interference is low enough to satisfy the minimum SIR requirement. We will see that GSM

requires M



3, while cdmaOne can operate with M

Why is a low cluster size good? By operating with a smaller number of cells in a cluster

the number of channels per cell, equal to

(

)(

)

, is high, since M is low. The carried

Cluster 1

Cluster 2

Figure 1.4: Two tesselated four-cell clusters.

1.2. MULTIPLE CELLS

trafﬁc in Erlangs for a given blocking probability has a non-linear relationship with the

number of channels per cell such that for more channels there is a disproportionate increase

in the trafﬁc that may be supported. We now observe an important aspect of cellular radio,

i.e. for a mobile radio system that employs clusters of cells. If the radio link equipment is

capable of operating with a low SIR, the cluster size becomes small and the carried trafﬁc

high. Another important point to note is that a cell becomes smaller in the presence of

cochannel interference. By this we mean that the area around the cell site where the SIR is

high enough to yield a sufﬁciently low bit error rate (BER) is decreased due to the presence

of the interfering cells. This is illustrated in Figure 1.5. We also note that as the levels of

interference power alter, so does the SIR, and so does the effective cell boundary for an

acceptable BER. The cell boundaries shown in Figure 1.5 relate to a speciﬁc BER. For a

higher BER, the cell size increases and vice versa. It is important to avoid the simple notion

that a cell has a ﬁxed area. It is better to think of it as breathing, i.e. changing its size

as the trafﬁc conditions within the network vary. Cell breathing is a feature of both GSM

and cdmaOne, although it is more acute in the CDMA system. For analysis reasons we

generally consider ﬁxed cells and often worse case conditions.

Newcomers to cellular radio often consider spectral efﬁciency in terms of the number of

channels, N, a carrier can support in a given bandwidth. This notion is related to modulation

efﬁciency in terms of bits per second per Hertz of RF bandwidth. Since cellular radio

must operate in an interference-limited environment, the crucial factor is not the modulation

efﬁciency. For example, employing quadrature amplitude modulation (QAM), where each

symbol carries multiple bits, gives a high modulation efﬁciency [10, 14]. However, QAM

requires a high SIR value and hence large cluster sizes, resulting in low values of carried

trafﬁc per cell site, for a given bandwidth allocation. The choice of modulation and multiple

access scheme is complex and will be addressed at a later stage. What we must note is that,

given a modulation and multiple access scheme resulting in a cluster size of M, the number

of users on the network is greatly increased if the cells, and thereby the clusters, are small.

This is because each cluster carries a trafﬁc of MA

Erlangs, where A

is the carried trafﬁc

at each BS, and if a cluster occupies an area S

then the trafﬁc carried per km

is MA

Erlangs/km

for a bandwidth W. Using small cells, often called microcells, means S

small and the trafﬁc density that may be supported is high.

1.2.1 Hexagonal cells

These types of cells are conceptual. The cell site is located at the centre of each hexagon,

and the hexagonal cells are tessellated to form clusters [15]. Although these cells are ﬁc-

titious, they are often used for comparing the performances of different cellular systems.

Figure 1.6 shows clusters of tessellated hexagonal cells. Observe that for hexagonal cells

there are always six near cochannel cells, irrespective of the cluster size. This is because

剩余520页未读，继续阅读

commthu

粉丝: 5
资源: 7

移动通信系统：从2G到3G的演变——GSM与cdmaOne

GSM,cdmaOne and 3G Systems

W-CDMA and cdma2000 for 3G Mobile Networks 2002.pdf

GSM移动通信概述.ppt

GSM向3G演进：HSCSD与GPRS技术详解

GSM移动通信系统解析：从IMSI到3G演进

GSM系统IMEI查询详解

3G演进：从2G到3G的革命

GSM移动通信系统原理详解

GSM移动通信系统原理概览

GSM移动通信系统原理与发展概述

最新资源