Wireless Wide Area Networks Continued 2
Fourth Generation Technologies
As the major network operators have just started providing 3G services, some groups and companies have already started working on fourth-generation mobile-phone system. The 4G technology will take mobile communication another step up to integrate radio and television transmissions, and to consolidate world's phone standards into one high-speed technology.
There are two key elements which are required to deliver a legitimate 4G network. First is the ability to roam across different wireless network standards with the one device; and the second, and most obvious, is a higher level of bandwidth. Figures of 100 Mbps have been tossed around, but a more reasonable figure to expect is about 20 Mbps.
At present, there are two competing 4G standards: a joint effort by Hewlett Packard and Japan's NTT DoCoMo to create Moto-Media, and the Wireless World Research Forum specifications with the backing of some of the Europe's largest phone makers.
The questions engaging most observers at the moment are just how big is the 4G market going to be, and when can the industry be reasonably expected to invest in a new network. Some of the analysts have estimated that the 4G mobile systems will have 50 million subscribers by the end of year 2007, and it would account for 14 percent of total mobile data revenues. But most of the analyst estimate the technology to be ready around 2008-2010. Nokia and Samsung have already teamed up to create 4G wireless equipment, a move which demonstrates the support for the 4G mobile systems.
Comparison of Data Services
The demand for mobile data services is growing. Increased mobility has fuelled an expanding market for both consumers and the enterprises. A comparison of various data services for cellular networks is shown in Table 4. For consumers, second-plus and third generation networks will bring access to the Internet, with near wire-line speed and quality. 2.5G services will mostly be text-based with still images and short audio clips. Services will include web browsing, financial transactions, image downloads, e-mail and instant messaging. As networks migrate to 3G, these same services will be enriched with multimedia content including full audio and video clips.
Table 4: Comparison of Data Services for 2G, 2.5G and 3G Networks
2ND + GENERATION
Short text screens
100KB web page takes approx. 30 sec to download
100KB web page takes approx. 2 sec to download
500 KB document takes approx. 2mn to download
500 KB document takes approx 10 sec to download
Short Message Service (SMS)
Text-based with small attachments
With audio/video clips
VoIP (Voice over IP)
Access to corporate intranet
Access to corporate apps
For enterprises, second-plus generation networks will allow access to corporate intranet and e-mail, business applications and databases, and increasing mobile sales and field employees’ productivity. In the future, 3G capabilities will enable even greater benefits from wireless business applications through VoIP (Voice over IP), rapid file transfer and video-conferencing.
PACKET SWITCHED MOBILE DATA NETWORKS
A packet switched mobile data network is a type of specialised mobile radio system which functions as a wireless wide-area data-only network for the mobile professionals. Like first generation cellular telephone systems, these packet radio systems use analogue radio technology. Unlike cellular systems, however, these networks offer connectionless support – subscribers do not maintain a dedicated, point-to-point connection to the destination station. Subscribers using the packet radio system are billed a monthly fee, plus a usage fee based on the amount of information (packets) transmitted through the system. The primary packet data services currently available in United States for mobile applications include ARDIS, MOBITEX, and a number of other services based on CDPD (Cellular Digital Packet Data) technology. A brief discussion of these services is given below:
ARDIS (Advanced Radio Data Information Services)
The ARDIS is a two-way radio service that is based on Motorola's RD-LAP technology. It was originally created and jointly owned by Motorola and IBM to serve IBM field technicians. However, later it was made available to the public. In 1998, it was acquired by the American Mobile Satellite Corporation. ARDIS support data transfer rate of 19.2 Kbps in urban areas, where it has 90% coverage of U.S business population (business population is considered the top 200-300 metro areas). Outside of those areas service can still be achieved, albeit at a lower 4.8 Kbps data rate. Due to overhead burdens associated with the radio channel protocol and error correction, subscriber data throughputs are actually much less than the raw data rate. Moreover, the network latency is fairly high. These limitations make the network unsuitable for most Internet and corporate intranet applications.
MOBITEX protocol was originally developed by Swedish Telecom as a private mobile alarm system used by field personnel. However, later it evolved into a public mobile radio service. Commercial operation was introduced in Sweden in 1986 and, since then, a number of networks have been deployed in U.K, U.SA, Canada, Australia and Scandinavian countries. In United States, the MOBITEX was introduced by RAM Mobile Data which is now a wholly owned subsidiary of BellSouth Wireless Data.
MOBITEX covers about 93% of the U.S. business population, making it a serious contender for some applications. Originally, MOBITEX transmission rate was 4.8 Kbps but now it has been upgraded to 19.2 Kbps. However, similar to ARDIS, the subscriber data throughput is much less than the raw data rate due to data transmission overhead. Moreover, network latency is fairly high - often several seconds. For these reasons, it is suitable only for limited text messages, not graphics or file transfers.
CDPD (Cellular Digital Packet Data)
CDPD specification was developed by a consortium of eight U.S. cellular companies. It allows data transmission to be overlaid onto the existing analogue cellular channels. It provides two significant enhancements to the AMPS cellular system – increased total system capacity and specifications for implementing data. CDPD networks are operated by various carriers in United States, including AT&T Wireless, Ameritech, Bell Atlantic Mobile and GTE.
CDPD offers standard RSA encryption over the air-link, making it the network of choice for public safety agencies and point of sale cash transactions. It offers users a raw data rate of 19.2 Kbps. However, overhead for coding and channel management to handle frequency hopping will reduce actual throughput. The reliability of CDPD data speeds is also questionable, particularly in mobile situations. Network-induced latency can be high, often more than one second. These limitations have made CDPD most useful for specific vertical-market applications.
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Mobile Networks 2
AVL Process Diagram