Smart-Phone-Cards Blog

Code division multiple access, simply called as CDMA is the technology used for radio communication in the present day mobile phones. This multiple access scheme allows sending of voice, data and signals for digital radio. The channels in this technology are defined with the use of PN sequences. The major advantage with this technology is the use of same frequency channel rather than the TDMA used in GSM devices. This facility allows several mobile phones to be controlled by a few cell sites and hence, CDMA is an economical technology for mobile phones.

Numerous standards have been developed for the CDMA technology. The latest standard used in mobile phones is the CDMA2000, which is compatible with the earlier standards. The CDMA standard is a proprietary standard developed by the Qualcomm telecommunication company in the United States in the year 1993. This technology is used in the mobile phones of North America and several parts of Asia. The improvements made to the standard make it possible to use in the latest generation mobile phones, which require higher data transfer rate. Transmission speed is important in the case of modern wireless devices.

The CDMA is superior to GSM in terms of time signals. CDMA devices can send accurate time signals and hence, CDMA is preferred for most of the global positioning system (GPS) which utilizes the accurate time signals. These CDMA signals can be referenced inside the buildings without the need for any antenna outside the building.

The terrains and the number of subscribers determine the coverage offered by CDMA. In cities where the population is dense, high frequencies are used and many small cell sites are installed. In the rural areas, low frequencies are used with limited cell sites for broader coverage. CDMA is also used to provide fixed-line networking, making use of the wireless local loop technology.

When you use your CDMA mobile phone to initiate a call, a communication is initiated between the mobile and the fixed base station. After establishing the communication, the movement of the destination mobile is estimated and the service is handed over the other base station. Only one cell at a time gets access to the mobile device. CDMA solves the increasing capacity problem with other radio standards. In CDMA, each user is allocated a distinct instance of noise carrier. No separate spectrum or time slot is needed for every user with CDMA.

No single technology fits with all the telecommunication devices. CDMA devices provide inter operability and the forward and backward compatibility. The standard has been improved to accommodate the demands of wireless networks. The 3G technology can work efficiently to transmit voice and broadband data using the CDMA technology. The mobile broadband service providers see CDMA as the economical and easy to deploy technology. However, GSM technology is also improved and it has its own huge number of subscribers in other parts of America. The efficient use of limited available spectrum makes CDMA, a leader in the mobile phone technology standards.

The General Packet Radio Service or GPRS is a telecommunications technology that is presently transforming the present shape of mobile communications. GPRS is a packet oriented Mobile Data Service providing data rates from 56 up to 114 kbit/s. Users of IS-36 mobile phones and Global System for Mobile Communications (GSM) can readily avail of this service.

How does a GPRS work? A GPRS connection is linked by orientation to its Access Point Name (APN). The APN then identifies the appropriate services like Wireless Application Protocol (WAP) access, Multimedia Messaging Service (MMS), Short Message Service (SMS), and for Internet communication services such as World Wide Web access and email. The charge for GPRS data transfer is per megabyte of traffic transferred as compared to data communication via traditional circuit switching that is charged per minute of connection time, whether or not the capacity is used or is in an idle state. Thus, as compared to circuit switching, GPRS is a best-effort packet switched service providing a certain Quality of Service (QoS) that is guaranteed in the link for non-mobile clients.

What are the basic features of GPRS? Frequency division duplex of FDD and TDMA provide multiple access methods used in GSM and GPRS. When a session is ongoing, a user is assigned to a pair of down-link and up-link frequency channels that is combined with time domain statistical multiplexing. This is done through packet mode communication making it feasible for more users to use the same frequency channel. To correspond to the GSM time slot, the packets have constant length. The down-link follows a first-come-first served packet scheduling and on the other hand, the up-link uses a mechanism close to reservation ALOHA. Meaning, the slotted Aloha (S-ALOHA) during a contention phase is used for reservation inquiries while a dynamic TDMA is used to transfer the actual data with first-come first-served scheduling.

What are the different types of connections to GPRS? Today there are various types with distinct features that exist in the market:

Class A can be linked to GPRS and GSM services (voice, SMS), where both can be used at the same time. Class B can also be linked to GPRS and GSM service (voice, SMS), however only one can be used at a given time thus, suspending the GPRS service during GSM service (voice call or SMS), and only then will it automatically resume after the GSM service has concluded. This class covers most GPRS mobile devices. Class C must be switched manually between GPRS service or GSM service since it is connected to either.

How does GPRS upgrade GSM data services? The GPRS supports GSM data with Multimedia Messaging Service (MMS), push to talk over Cellular PoC/PTT, in the wireless village an instant messaging and presence feature, access of Wireless Application Protocol (WAP) in Internet Applications for Smart devices, Short Message Services or SMS, and further enhances new functions such as higher capacity, new protocols, new accesses and new radio networks.

The channel encoding used will dictate the GPRS speed transfer. The fastest however least robust coding scheme (CS-4) is accessible when in proximity to a base transceiver station (BTS). Going further away from the BTS though gives the most robust coding scheme (CS-1).