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Voice and Messaging
|by Ruchi Gupta|
Whether its because you made a call using a mobile phone, received a message on your pager, checked your email from a PDA or even just seen a advert related to it, we have all come across a wireless data or voice network. Wireless technologies represent a rapidly emerging area of growth and importance for providing ubiquitous access to the network for all those who want to use wireless services.
All the above classifications are based on the cost, network model, bandwidth, and coverage areas. In this article we will discuss about Voice and Messaging part of wireless technologies.
Mobile phones, pagers, and two-way business radios comes under voice and messaging services. These devices can further be divided into two categories depending on what standards they are based on either it can be analog or digital which again depends on in the way in which they process signals and encodes information.
The analog standard is Advanced Mobile Phone System (AMPS). Digital standards are Global System for Mobile Communications (GSM), or Code Division Multiple Access (CDMA).
These devices operate within networks and different carriers operate these network. In USA there are carriers like AT&T, Sprint, Verizon, local phone companies etc. and operate in different frequency band, which are allocated by Federal Communication Commission (FCC), this commission regulates interstate and international communications by radio, television, wire, satellite and cable.
Advance Mobile Phone System (AMPS)
This is the analog mobile phone system standard developed by Bell Labs, and officially introduced in USA in 1984. Now a day analog is not considered advanced but at that time it was considered quit advanced and its introduction is what made today’s mobile world practical.
This standard is based on the initial electromagnetic radiation spectrum and allocates frequency ranges within the 800 and 900 Megahertz (MHz) spectrum to cellular telephone.
Each service provider can use half of the frequency range for receiving signals from cellular phones and half for transmitting to cellular phones. The bands are divided into 30 kHz sub-bands called channels. The receiving channels are called reverse channels and the sending channels are called forward channels.
This division of the spectrum into sub-band channels is achieved by using Frequency Division Multiple Access (FDMA).
FDMA is the technique where available bandwidth is divided into a multitude of channels where each user occupies a separate channel.
Global System for Mobile Communications (GSM)
With analog system there were many disadvantages with cellular communication like it didn’t support encryption, compression, and ISDN compatibility. In early 80s European realized that new mobile system should be developed that should be digital, ISDN compatible with good speech quality. From here the introduction of GSM to the world started.
GSM network operates in the frequency range of 1,850 to 1,990 MHz, and the separation between adjacent carrier frequencies is 200 kHz.
GSM utilizes the time division multiple access concept (TDMA). TDMA is a technique in which several different calls may share same carrier and each call is assigned a particular time slot.
In United States T-mobile and Cingular etc. are the carriers of GSM network on 1,900 MHz band.
Code Division Multiple Access (CDMA)
CDMA is a digital wireless technology that works by converting speech into digital information, which is then transmitted as a radio signal over a wireless network. Using a unique code to distinguish each call, CDMA uses spectrum efficiently, enabling more people to share the airwaves simultaneously without static, cross talk or interference. The foremost application of CDMA is the digital cellular phone technology from QUALCOMM that operates in the 800MHz band and 1.9GHz PCS band. CDMA phones are noted for their call quality.
CDMA optimizes use of the radio spectrum, which is an increasingly scarce resource worldwide. CDMA requires fewer cell sites than the GSM and TDMA digital cell phone systems. CDMA's single cell frequency re-use capability and non-contiguous bandwidth requirement, along with its extended coverage range, simplifies RF planning and implementation. This allows providers to deploy faster, and giving the opportunity to service provider for increased and quicker return on investment. In United States CDMA Network Operators are ALLTEL, Verizon Wireless, US Cellular and the Qwest communications.
So which is better? Its like comparing AM and FM radio they both do the same thing but differently.
The wireless world offers broad choices among service providers, calling plans and phones. Low-priced equipments and rates make wireless affordable. Today’s cell phones comes with so many other features besides talking like you can take photos, surf the Internet, send emails, play games and many more. With so many options available in the market, its only you who have to decide which one is suitable for you.
|More by : Ruchi Gupta|
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