~ First Handheld Phone

Technology Explained

…  FDMA: Frequency Division Multiple Access (FDMA) is the most common analog system.  It is a technique whereby spectrum is divided up into frequencies and then assigned to users.  With FDMA, only one subscriber at any given time is assigned to a channel.  The channel therefore is closed to other conversations until the initial call is finished, or until it is handed-off to a different channel.  A ìfull-duplexî  FDMA transmission requires two channels, one for transmitting and the other for receiving.  FDMA has been used for first generation analog systems.

…  TDMA Systems. TDMA-based systems divide a radio frequency (RF) channel into time slots, each of which lasts for a fraction of a second, and then allocates those slots to multiple calls. TDMA divides a 30-KHz channel into six time slots that are allocated in pairs, resulting in three usable TDMA channels. Any given conversation can use one or more of every third time slot on an ongoing basis during a call.

TDMA delivers short message service (SMS), and has a data capacity of about 9.6-Kbps. Ericsson, Lucent Technologies and Nortel Networks are the largest vendors of TDMA-based equipment, and Cingular is the largest TDMA carrier in the United States.

…  GSM Systems. To standardize the cellular phone system throughout Europe, Groupe SpÈcial Mobile (now called Global System for Mobile Communications) was formed. The greatest strength of this nonproprietary system is its international roaming capability. Users have seamless, same-number roaming in more than 170 countries.

Most GSM systems operate in the 900-MHz and 1.8-GHz frequency bands, except in North America where they operate in the 1.9-GHz band. GSM uses a combination of FDMA and TDMA multiple access schemes on its 25-MHz-wide frequency spectrum. FDMA divides the 25-MHz bandwidth into 124 carrier frequencies of 200 KHz each. Each 200-KHz channel is then divided into eight time slots using TDMA. GSM systems support data speeds of 9.6 Kbps and the SMS feature. The prominent vendors of GSM equipment are Alcatel, Ericsson, Lucent, Nokia and Nortel. VoiceStream Wireless is the largest provider of GSM in this country.

…  CDMA Systems. Developed by Qualcomm, CDMA is a 2G technology that uses digital encoding and spread-spectrum RF techniques to let multiple users share the same RF channel. CDMA divides the radio spectrum into channels that are 1.25-MHz wide, larger than that in typical AMPS or TDMA systems.

CDMA differentiates each user's signal by encoding it uniquely. At the transmitting end, this is used to encode the signal, which is then spread across the frequency spectrum. At the receiving end, this code is detected and used to extract the user's information.

Existing IS-95-based CDMA systems, also called cdmaOne, support circuit-switched data services at speeds of 9.6 Kbps to 14.4 Kbps. The IS-95A protocol supports data speeds of up to 14.4 Kbps. IS-95B is a next-generation transitional step from the IS-95A CDMA standard and offers data rates of about 64 Kbps while maintaining compatibility with existing IS-95A systems. In the United States, Lucent, Motorola and Nortel are the biggest CDMA equipment vendors, and Sprint PCS and Verizon Wireless are the largest CDMA carriers.

CDMA increases system capacity by about 10 to 15 times compared with AMPS and by more than three times compared with TDMA. Other strengths include improved voice quality, greater capacity and enhanced privacy.

3G technology will join the different 2G wireless systems into a global system providing data rates of about 2 Mbps. CDMA has emerged as the multiple access scheme of choice for 3G. The proposed 3G evolution path for TDMA-based systems, including GSM, is W-CDMA (Wideband CDMA), a standard proposed by Ericsson, while CDMA systems will evolve to CDMA 2000 systems. W-CDMA will incorporate an airlink that uses a 5-MHz-wide carrier to enable systems to support speeds of up to 3 Mbps; CDMA 2000 will combine three 1.25-MHz carriers to accomplish its rates.

Team 10
Bill Edmonds, Leslie Fuchs, Andrew Lindsay, Vickie Miller, Bjarke Ormstrup