CMDA

Also see CDMA One, CDMA2000, and WCDMA. Compare time-division multiplex (TDM) and frequency-division multiplex (FDM).
CDMA (code-division multiple access) refers to any of several protocols used in so-called second-generation (2G) and third-generation (3G) wireless communications. As the term implies, CDMA is a form of multiplexing, which allows numerous signals to occupy a single transmission channel, optimizing the use of available bandwidth. The technology is used in ultra-high-frequency (UHF) cellular telephone systems in the 800-MHz and 1.9-GHz bands.

CDMA employs analog-to-digital conversion (ADC) in combination with spread spectrum technology. Audio input is first digitized into binary elements. The frequency of the transmitted signal is then made to vary according to a defined pattern (code), so it can be intercepted only by a receiver whose frequency response is programmed with the same code, so it follows exactly along with the transmitter frequency. There are trillions of possible frequency-sequencing codes; this enhances privacy and makes cloning difficult.

The CDMA channel is nominally 1.23 MHz wide. CDMA networks use a scheme called soft handoff, which minimizes signal breakup as a handset passes from one cell to another. The combination of digital and spread-spectrum modes supports several times as many signals per unit bandwidth as analog modes. CDMA is compatible with other cellular technologies; this allows for nationwide roaming.

The original CDMA standard, also known as CDMA One and still common in cellular telephones in the U.S., offers a transmission speed of only up to 14.4 Kbps in its single channel form and up to 115 Kbps in an eight-channel form. CDMA2000 and wideband CDMA deliver data many times faster.

TDMA

TDMA (time division multiple access) is a technology used in digital cellular telephone communication that divides each cellular channel into three time slots in order to increase the amount of data that can be carried.

TDMA is used by Digital-American Mobile Phone Service (D-AMPS), Global System for Mobile communications (GSM), and Personal Digital Cellular (PDC). However, each of these systems implements TDMA in a somewhat different and incompatible way. An alternative multiplexing scheme to FDMA with TDMA is CDMA (code division multiple access), which takes the entire allocated frequency range for a given service and multiplexes information for all users across the spectrum range at the same time.

TDMA was first specified as a standard in EIA/TIA Interim Standard 54 (IS-54). IS-136, an evolved version of IS-54, is the United States standard for TDMA for both the cellular (850 MHz) and personal communications services (1.9 GHz) spectrums. TDMA is also used for Digital Enhanced Cordless Telecommunications (DECT).

GSM

GSM (Global System for Mobile communication) is a digital mobile telephone system that is widely used in Europe and other parts of the world. GSM uses a variation of time division multiple access (TDMA) and is the most widely used of the three digital wireless telephone technologies (TDMA, GSM, and CDMA). GSM digitizes and compresses data, then sends it down a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1800 MHz frequency band.

GSM is the de facto wireless telephone standard in Europe. GSM has over 120 million users worldwide and is available in 120 countries, according to the GSM MoU Association. Since many GSM network operators have roaming agreements with foreign operators, users can often continue to use their mobile phones when they travel to other countries.

American Personal Communications (APC), a subsidiary of Sprint, is using GSM as the technology for a broadband personal communications service (PCS). The service will ultimately have more than 400 base stations for the palm-sized handsets that are being made by Ericsson, Motorola, and Nokia. The handsets include a phone, a text pager, and an answering machine.

GSM together with other technologies is part of an evolution of wireless mobile telecommunication that includes High-Speed Circuit-Switched Data (HCSD), General Packet Radio System (GPRS), Enhanced Data GSM Environment (EDGE), and Universal Mobile Telecommunications Service (UMTS).

Air Interface Technologies

3G CDMA2000

Third Generation (3G) is the term used to describe the latest generation of mobile services which provide advanced voice communications and high-speed data connectivity, including access to the Internet, mobile data applications and multimedia content. The International Telecommunication Union (ITU), working with industry standards bodies from around the world, has defined the technical requirements and standards as well as the use of spectrum for 3G systems under the IMT-2000 (International Mobile Telecommunications-2000) program.

The ITU requires that IMT-2000 (3G) networks, among other capabilities, deliver improved system capacity and spectrum efficiency over 2G systems and that they support data services at minimum transmission rates of 144 kbps in mobile (outdoor) and 2 Mbps in fixed (indoor) environments.

Based on these requirements, in 1999 the ITU approved five radio interface modes for IMT-2000 standards (Recommendation 1457). Three of the five approved standards (CDMA2000® , TD-SCDMA, WCDMA) are based on CDMA. CDMA2000 is also known by its ITU name, IMT-2000 CDMA Multi-Carrier (MC).

The world's first 3G commercial system was launched by SK Telecom (South Korea) in October 2000 using CDMA2000 1X. By the end of 2006 there will be more than 430 million 3G users across all six continents, In Korea, Japan and North America there are already more 3G users than 2G subscribers, and globally the number of 3G subscribers is expected to surpass 2G in 2011, ten years since 3G’s inception and 5 years less than it took 2G to surpass 1G.

CDMA2000 Technologies

CDMA2000 represents a family of standards and includes:

CDMA2000 1X
CDMA2000 1xEV-DO Technologies
CDMA2000 1xEV-DO Rel 0
CDMA2000 1xEV-DO Rev A
CDMA2000 1xEV-DO Rev B
Ultra Mobile Broadband - UMB
CDMA2000 builds on the inherent advantages of CDMA technologies and introduces other enhancements, such as Orthogonal Frequency Division Multiplexing (OFDM and OFDMA), advanced control and signaling mechanisms, improved interference management techniques, end-to-end Quality of Service (QoS), and new antenna techniques such as Multiple Inputs Multiple Outputs (MIMO) and Space Division Multiple Access (SDMA) to increase data throughput rates and quality of service, while significantly improving network capacity and reducing delivery cost.

Key features of CDMA2000 are:

Leading performance: CDMA2000 performance in terms of data-speeds, voice capacity and latencies continue to outperform in commercial deployments other comparable technologies
Efficient use of spectrum: CDMA2000 technologies offer the highest voice capacity and data throughput using the least amount of spectrum, lowering the cost of delivery for operators and delivering superior customer experience for the end users
Support for advanced mobile services: CDMA2000 1xEV-DO enables the delivery of a broad range of advanced services, such as high-performance VoIP, push-to-talk, video telephony, multimedia messaging, multicasting and multi-playing online gaming with richly rendered 3D graphics
All-IP – CDMA2000 technologies are compatible with IP and ready to support network convergence. Today, CDMA2000 operators that have deployed IP-based services enjoy more flexibility and higher bandwidth efficiencies, which translate into greater control and significant cost savings
Devices selection: CDMA2000 offers the broadest selection of devices and has a significant cost advantage compared to other 3G technologies to meet the diverse market needs around the world
Seamless evolution path : CDMA2000 has a solid and long-term evolution path which is built on the principle of backward and forward compatibility, in-band migration, and support of hybrid network configurations
Flexibility: CDMA2000 systems have been designed for urban as well as remote rural areas for fixed wireless, wireless local loop (WLL), limited mobility and full mobilility applications in multiple spectrum bands, including 450 MHz, 800 MHz, 1700 MHz, 1900Mhz and 2100 MHz
CDMA2000 Advantages

Superior Voice Clarity
High-Speed Broadband Data Connectivity
Low End-to-End Latency
Increased Voice and Data Throughput Capacity
Time-to-Market Performance Advantage
Long-Term, Robust and Evolutionary Migration Path with Forward and Backward Compatibility
Differentiated Value-Added Services such as VoIP, PTT, Multicasting, Position Location, etc.
Flexible Network Architecture with connectivity to ANSI-41, GSM-MAP and IP-based Networks and flexible Backhaul Connectivity (see the text at the end – we can do that later)
Application, User and Flow-based Quality of Service (QoS)
Flexible Spectrum Allocations with Excellent Propagation Characteristics
Robust Link Budget for Extended Coverage and Increased Data Throughputs at the Cell Edge
Multi-mode, Multi-band, Global Roaming
Improved Security and Privacy
Lower Total Cost of Ownership (TCO)