Shulou(Shulou.com)06/01 Report--

When people talk about cellular technology, they often classify it as belonging to a certain generation. Earlier generations of technologies were mainly designed for voice traffic, and some recent cellular systems also support Internet access in addition to voice. Recent generations have evolved directly from previous generations, so we briefly review the first and second generation wireless systems.

The first generation (1G) system is an analog FDMA system designed only for speech. These 1G systems have basically disappeared and have been replaced by 2G digital systems.

1. Second generation (2G)

Although the second generation system is digital, it is also designed for voice communication. Since 2.5G and 3G, currently designed to handle data communications, are derived from 2G, it is important to briefly introduce 2G. The 2G cellular phone first converts the analog signal into a digital signal, then modulates the signal and transmits it into the air. A variety of 2G standards and technologies have been widely deployed, including:

(1) Global system for Mobile Communications (Global System for Mobile Communication,GSM). In the 1980s, Europe recognized the need for a pan-European digital system to replace its incompatible 1G system, providing seamless mobility between different countries and other features and functions that analog systems do not have. This demand has spawned the GSM standard for bee communications. Europe deployed GSM technology very successfully in the early 1990s. Then GSM expanded to Asia and North America, and now it has become the most widely used cellular communication standard. The GSM of 2G cellular system has been extended to Asia and North America, and has become the most widely used cellular communication standard. The GSM standard of 2G cellular system is the combination of air interface and FDM/TDM. The GSM system consists of 200kHz bands, each of which supports 8 TDM calls. GSM encodes speech at 13kbps and 12.2kbps rates.

(2) IS-95 CDMA. IS-95 CDMA uses code division multiple access. Qualcomm demonstrated the viability of CDMA for cellular phones in the late 1980s, and many IS-95 systems began to be deployed, especially in North America and South Korea.

two。 The transition from the second generation to the third generation (2.5G)

2G systems such as IS-95 and GSM are optimized for voice services and are not particularly suitable for data communications. In the 1990s, standardization organizations recognized the need for 3G cellular technologies that are suitable for both voice and data communications, including Internet access. Then, because it takes a long time to deploy 3G technology widely, some companies have developed intermediate protocols and standards that can transfer data over the existing 2G infrastructure. These systems are collectively referred to as "2.5G cellular systems". They include:

General packet Radio Service (General Packet Radio Service, GPRS). GPRS evolved from GSM. For data services, GSM effectively simulates the modem between the user equipment and the destination data network. In addition, the standard GSM supports only the most 9.6kbps data rates, which is too modern for any data except simple text. GPRS is an intermediate solution that provides more efficient, packet-based data services with higher data rates (usually 40~60kbps), and in many ways can be used to connect a home PC dial-up to the Internet in the same way as a home phone. Therefore, GSM uses circuit switching for standard voice and data (connecting user equipment to the Internet). GPRS services are provided by the underlying GSM network. However, unlike ordinary GSM, mobile GPRS stations can use multiple time slots in a channel as needed. In GPRS, many time slots are set aside for data communication and dynamically allocated according to the immediate request of the mobile station.

(2) enhanced data rates (Enhanced Data Rates for Global Evolution, EDGE) that support global evolution. The main purpose of EDGE is to increase the data rate of GSM/GPRS network, that is, to make better use of the channel of GSM 200kHz with 8 slotted TDMA frames. This is mainly through a more effective mechanism to replace the modulation mechanism of GSM. In theory, EDGE can provide the data rate of 384kbps for the trust of user data.

(3) CDMA 2000 Phase 1. This 2.5G technology evolved from IS-95. It can provide packet data services at rates as high as 144.4kbps, and lays the foundation for the deployment of 3G in CDMA 2000 Phase 2.

3. The third generation (3G)

3G cellular systems are required to provide telephone services and data communications at much higher speeds than their corresponding 2G systems. In particular, 3G systems require that:

(1) the speed of driving reaches 144kpbs.

(2) the speed of outdoor rest or walking reaches 384kbps.

(3) the indoor speed reaches 2Mbps.

There are two main (and competing) standards in 3G:

(1) CDMA-2000. CDMA-2000 evolved from the IS-95 2G system and is backward compatible with IS-95. It can be inferred from its name that it also uses CDMA as part of its space interface. CDMA-2000 is being deployed in North America and parts of Asia. The data service associated with CDMA-2000 is called 1xEVDO (Evolution Data Optimized-- Evolutionary data Optimization, which is one of the worst acronyms!) The expected data rate is of the order of 3Mbps.

The opportunistic scheduling technology we encountered in the previous WiMAX standard was actually developed previously for EVDO and its CDMA-2000-HDR (high data rate) predecessor.

(2) General Mobile Telecom (Universal Mobile Telecommunications Service, UMTS). UMTS is the evolution of GSM to support 3G capabilities. The UMTS network architecture draws lessons from many established GSM network architectures. However, the radio access of UMTS is very different from the FDMA/TDMA scheme used in GSM. Specifically, UMTS uses a CDMA technology called Direct sequence Broadband CDMA (DS-WCDMA) (frames of TDMA slots are available on multiple frequencies, which is an interesting use of all three specialized channel sharing methods we pointed out earlier). Since UMTS comes from GSM, it's not surprising that UMTS is being widely deployed in Europe. The data service related to WCDMA specification is called HSDPA/HSUPA (High Speed Uplink / Downlink packet access), and the data rate is expected to reach 14Mbps. Like EVDO, HSDPA/HSUPA uses opportunistic scheduling and other advanced technologies.

4. The fourth generation (4G)

Now that we have analyzed wireless LAN technology and all cellular access technologies, let's take a step back and think about what our ideal wireless Internet access would be like as users. Here are some wishes:

(1) We want ubiquitous wireless Internet access. We want to be able to access the Internet at home, in the office, in the car, in the coffee shop, or on the beach.

(2) the Internet access rate is a function of the physical and mobile speed, and we hope to be able to access the Internet at the highest possible rate.

(3) when roaming through a heterogeneous environment, we can automatically and transparently switch from one access technology to another, which only depends on availability and does not require the intervention of any users.

(4) of course, we want to maintain an ongoing TCP connection during the move. Further, we want the system to know where we are so that new calls can continue to reach us as we move.

(5) We want the system to support voice and real-time video on IP.

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