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外文文献译文
设计(论文)题目: 基于NS的通用移动通信系统模拟平
台研究与实现的设计
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Mobile communications fundamental
TIA Interim Standard 136 (IS-136) evolved from IS-54 and is also called just TDMA or Advanced MobilePhone Service (D-AMPS) on the market. It is a purely digital system, but still uses the channel bandwidth of 30 kHz introduced by AMPS. The main difference between IS-54 and acIS-136 is, that IS-136 uses TDMA also on the control channels. In December 2001, the number of mobile subscribers using IS-136 technology was 94.4 million worldwide according to figures given by[7]. This represents 10% of the worldwide subscriber base. IS-136 networks are mainly operational in North and South America, the Caribbean and in Asia.
The other systems are IS-95 systems that represent the first commercially operated Code Division Multiple Access (CDMA) systems. This transmission technology, which originates from military communication technology, also forms the basis for the radio interface in Universal Mobile Telecommunication System (UMTS) and will be looked at in detail in Chapter 6. With a channel bandwidth of 1.23 MHz, IS-95 systems are relatively narrowband systems and therefore are also referred to as narrowbandCDMA (N-CDMA).
In addition to the US, IS-95 was also able to establish itself in South America,Central Africa and Asia. According to statistics published by the CDMA Development Group (www.cdg.org), over 90 million people used IS-95 systems to make calls in March 2001, of which more than 39 million lived in Asia and more than 33 million were in North America.
Figure 3.1: Worldwide distribution of 2nd generation mobile radio systems Japan also developed its own standard: Personal Digital Cellular (PDC).PDC also uses TDM A technology (3 time slots, 25kHz channel bandwidth) and operates at 800MHz and 1500MHz. The modern mobile telephones are small, sophisticated and
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offer long operating times. In June 2000 over 50 million Japanese people were using PDC. PDC-P is an enhancement that enables packet-switched data transmission with PDC at a transfer rate of up to28.8kbit/s. This technology is the basis for Japan's very successful i-Mode service, which offers access to Internet pages, emails and local information.Compared to other regions, Japan has a smaller distribution of Internet access than Europe or the US. Consequently, many subscribers use the service to call up information found elsewhere on the Internet. However, PDC had no success in expanding beyond the borders of Japan to other countries (see Figure 3.2).The i-Mode service, however, has been introduced in several European countries and is now competing against WAP Next Generation (WAP-NG) and MMS-based information services.
Probably the best-known system is one that originates in Europe and the use of which has spread from there to all parts of the world. Global System for Mobile Communications (GSM) was designed in the late 1980s by the state-owned national telecommunication companies and harmonised for use throughout Europe. The first systems started operating at 900 MHz (GSM900) in the early 1990s. This was followed by systems operating at 1900MHz (GSM1900) 3.1 From2Gto3G 25
Figure 3.2: 2nd generation mobile radio systems
in America and 1800MHz (GSM1800) in other counties. GSM also employs TDMA technology and uses 8 time slots on a 200 kHz wide carrier frequency.GSM900 has a total of 124 frequency channels and GSM1800 even has 374.GSM is used by over 400 operators in more than 171 countries in Europe,Asia, Australia, North and South Africa, and America. The projection of the GSM Association is that approximately
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one billion subscribers will be using this technology by the end of 2003.
These systems are currently competing for the mobile communication market.Each system incorporates its advantages and disadvantages, but one thing is common to all three: the systems were initially designed for narrowband speech telephony with bitrates between 5 and 15 kbit/s [24]. Now the emphasis is being shifted towards data services. Although the user numbers for wireless access to the Internet are still relatively low, this is an area where the next growth spurt is anticipated, especially considering that in some countries,more than 60% of the population are already using mobile telephones [33].
Even though multi-band and multi-mode devices are available, the different 2G systems are not compatible with one another, i.e., it is difficult and complicated to use different 2G systems worldwide.
If one looks at the reasons for the success of GSM, the main one is the open standardisation that was responsible for its initial success. Many of the ideas
Figure 3.3: A perspective of GSM
it incorporates show an incredible vision that has kept the system open for further enhancement and development. This has enabled GSM to adapt to new developments without becoming incompatible with existing products.
Because of the early entry of GSM to Europe, there was also an early market for infrastructure and terminals. This resulted in cost reductions that in turn contributed towards GSM's rapid growth. Today, the technology is being produced in very high quantities and therefore is extremely cost-effective.
Due to the wide distribution of GSM, the number of qualified personnel with experience in the set-up and operation of GSM networks has grown.Since its introduction to the market, GSM has continued to develop. The Half Rate Codec (HRC) increased capacity and the Enhanced Full Rate Codec (EFRC) improved voice
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