Wireless Ad Hoc and Sensor Networks

Background on Networking 13analog modulation scheme, was used in transmission of signalsbetween a user and a mobile.Second-generation (2G) cellular networks: Present cellular networksconform to the 2G cellular standards. The 2G cellular standardsemploy digital modulation formats and TDMA/FDD (time divisionmultiple access/frequency division duplexing) and CDMA/FDD(code division multiple access/frequency division duplexing)multiple access schemes. Of the many cellular standards proposed,four popular 2G standards have gained wide acceptance. These includethree TDMA standards and one CDMA standard. A brief descriptionof these standards is provided in the following paragraphs.GSM (global system mobile): GSM supports eight time-slotted usersfor each 200-kHz radio channel and has been deployed widelyin the cellular and personal communication systems (PCS) bandsby cellular service providers. It has been effectively deployed inAsia, Europe, Australia, South America, and in some parts of U.S.Interim standard 136 (IS-136): This cellular networking standard is alsocommonly known as North American digital cellular (NADC) orU.S. digital cellular (USDC), which supports three time-slottedusers for each 30-kHz radio channel and is a popular choice forcarriers in North America, South America, and Australia.Pacific digital cellular (PDC): It is a Japanese TDMA standard thatis similar to IS-136 with more than 50 million users.Interim standard 95 code division multiple access (IS-95): This popular2G CDMA standard supports up to 64 users that are orthogonallycoded or multiplexed. The signal generated from these 64users is simultaneously transmitted each on a 1.25-MHz channel.Mobile radio networks (2.5G): 2G cellular standards contain circuitswitcheddata modems that limit data users to a single circuitswitcheddata voice channel. Data transmissions in 2G are thusgenerally limited to the data throughput rate of an individualuser. These systems support only single-user data rates of theorder of 10 kbps.The need for high-speed data access rates called for improvement inthe 2G cellular system standard. Three different upgrade paths have beendeveloped for GSM carriers and two of these solutions support IS-136.The three TDMA upgrade options available include: (1) high-speed circuitswitched data (HSCSD), (2) general packet radio service (GPRS), and (3)enhanced data rates for GSM evolution (EDGE).The upgrade options for 2G cellular networks have provided significantimprovement in Internet access speed over GSM and IS-136 standards.HSCSD, the standard for 2.5G GSM, was able to provide a raw transmission