CDMA Testing - Standard Description, Measuring Instruments
Standard CDMA (an abbreviation for Code Division Multiple Access) - a code division multiple access system is one of the most promising communication standards today.
Over the past five years, CDMA technology has been tested, standardized, licensed and commercialized by most wireless equipment vendors and is already in use worldwide. Unlike other methods of subscriber access to the network, where signal energy is concentrated on selected frequencies or time intervals, CDMA signals are distributed in a continuous time-frequency space. In fact, CDMA manipulates frequency, time, and energy.
In CDMA systems, each voice stream is marked with its own unique code and is transmitted on the same channel simultaneously with many other encoded voice streams. The receiving side uses the same code to extract the signal from the noise. The only difference between multiple voice streams is the unique code. The channel is usually very wide and each voice stream occupies the entire bandwidth. This system uses 1.23MHz wide channel sets. Voice is encoded at 8.55kbps, but voice activity detection and different coding rates can cut down to 1200bps. CDMA systems can establish very strong and secure connections despite extremely low signal strength, theoretically the signal can be weaker than the noise level.
Varieties of CDMA technology
Standard cdmaOne, exists in variations IS-95a, IS-95b (cellular in American terminology, 800 MHz) and J-STD-008 (PCS, 1900 band). The abbreviation IS (interim standard - temporary standard) is used for accounting in the Telecommunications Industry Association TIA (Telecommunications Industry Association). As a rule, cdmaOne networks use IS-95a, it provides signal transmission at a speed of 9.6 kbps (with coding) and 14.4 kbps (without coding). The IS-95b version is based on combining several CDMA channels organized in the forward direction (from the base station to the mobile). The speed can be increased to 28.8 kbps (when combining two channels of 14.4 kbps) or up to 115.2 kbps (8 channels of 14.4 kbps). Actually, in addition to IS-95, cdmaOne networks also use a whole set of protocols and standards,
Commercial networks cdmaOne appeared in 1995 and enjoy well-deserved popularity both in their homeland, in America, and in Asia. It is cdmaOne that is meant by the terms "CDMA" and "CDMA-800" (it is the 800 MHz version, IS-95, that is most widely used). The forward and reverse channels are located respectively in the ranges of 869.040-893.970 and 824.040-848.860 MHz. 64 Walsh codes and 1.25 MHz carriers are used.
WCDMA (Wideband Code Division Multiple Access - broadband CDMA) is a radio interface technology chosen by most Japanese cellular operators and (in January 1988) by ETSI (European Telecommunications Standards Institute) to provide broadband radio access to support third generation services.
The technology is optimized to provide high-speed multimedia services such as video, Internet access and videoconferencing; provides access speeds up to 2 Mbps at short distances and 384 Kbps at long distances with full mobility, supports voice, image, data and video transmission. These data rates require a wide bandwidth, so the WCDMA bandwidth is 5 MHz. The technology can be added to existing GSM and PDC networks, making the WCDMA standard the most promising in terms of network resource utilization and global interoperability. WCDMA is used mainly in Europe during the transition from the GSM standard to the UMTS standard.
Standard cdma2000 is a further development of the 2nd generation cdmaOne standard. A further development of cdmaOne was to be IS-95c, and it is this designation that is very often used by manufacturers.
The official update to the standard developed by Qualcomm and approved by the ITU (International Telecommunication Union) is cdma2000. The designation IS-2000 is found in Lucent Technologies documents. Finally, the International Telecommunication Union (ITU) selected from ten proposed projects five radio interfaces of the third generation IMT-2000 (International Mobile Telecommunications System - 2000 - International Mobile Telecommunications System - 2000), including IMT-MC (Multi Carrier), which represents is a modification of the cdma2000 multi-frequency system that provides backward compatibility with cdmaOne (IS-95) equipment. Another of the five IMT-2000 standards - IMT-DS (Direct Spread) - is built on the basis of W-CDMA projects and is taken as the basis of the European UMTS system.
At the beginning of 2003 of the 127 million CDMA users, almost 15 million used cdma2000 technology. During the first seven months of 2002, 11 CDMA2000 networks were launched in Asia and America, and the total number of these networks was 18. This is 99% of the 3G market, IMT-MC accounted for 14.8 million subscribers, UMTS - 0.13 million. However, it is worth noting that the implemented cdma2000 1X phase is still not a full-fledged 3G, because it falls short of the required two megabits. Therefore, it is often called 2.5G.
The cdma2000 (IMT-MC) was originally split into two phases, 1X and 3X. It is to the first phase that the name IS-95C is applied. And the second one was later called 1X-EV (evolution), dividing it into two phases - cdma2000 1X EV-DO (data only) and cdma2000 1X EV-DV (data & voice). It is the cdma2000 1X EV-DO standard that is meant by 3G IMT-MC. The 1x-EV-DO standard was adopted by TIA in October 2000 and provides for the following operation scheme: the device simultaneously searches for a 1x and 1xEV network, transmits data using 1xEV, voice - using 1x. The 1xEV-DV standard fully complies with all 3G requirements.
The main components of the commercial success of the CDMA2000 system are a wider service area, high voice quality (virtually equivalent to wired systems), flexibility and low cost of introducing new services. This technology provides high noise immunity, stability of the communication channel from interception and eavesdropping, which makes it attractive to use for all categories of subscribers.
Devices Recommended for CDMA Testing