Hi there,
Found an interesting article which may be of interest to the RIM users. Would be interesting to hear views on this issue.
Melvyn
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http://www.techno-preneur.net/timeis/techn...3/hotfight.html
THE HOT FIGHT :: GSM Vs. CDMA
In past few years India has seen a large growth in its Telecom and Internet Infrastructure. The fixed line and Cellular Subscribers base has shown a steep rise. The cellular market in India has grown at the rate of 80-85 Per cent, and achieved a subscriber base of 10.4 million by end -2002. According to Cellular Operators Association of India (COAI), the industry has grown from Rs. 3,285 crore in FY 2000-2001 to Rs. 4,700 crore in FY 2001-2002. But with shot of CDMA arrow from Reliance, Is it that the fast growing cellular industry has started slowing down ? Today this is the billion-dollar question.
Working of GSM based Cellular
A large geographic area is subdivided into relatively small areas called cells. Each cell has a base station which transmits to and received from all mobile phones within the area of the cell. A base station is an antenna, similar to a microwave antenna. Each base station is connected to a mobile switching office by either a conventional terrestrial line or microwave relay. Each base station sends and receives signals from mobile phones located in their cell. Each adjoining transmitter uses a different frequency, but transmitters in nonadjacent cells use the same frequencies.
The mobile station is the subscriber end of network and consists of the GSM device (cell phone) and the Subscriber Identity Module (SIM). Each mobile device has a globally unique International Mobile Equipment Identity (IMEI) and each SIM has an International Mobile Subscriber Identity (IMSI), which is used to identify and authorize the subscriber for various services.
As a mobile user passes from one cell to another it must be assigned another voice channel very quickly so that the cell is not interrupted as the frequencies, change. The process of reallocating a different voice channel as a user moves between cells is called the "hand-off".
The mobile switching office is similar in operation to a conventional switching office in that it handles the switching of cells between mobil subscribers and calls to and from the public network. The principal functions of a mobile switching, routing and overall control, Interface with the conventional public network, Directory management, control of subscriber location and hand-off, Signaling control etc.
How does CDMA work?
CDMA works on the principle called interference averaging. Signals are spread uniformly over the entire available bandwidth. Different calls are assigned different codes. Together, they appear as noise-like interference to each other. During the receiving stage, when a particular call is decoded, this noise becomes supressed. In other words, the interference is one of the limiting factors, its averaging results in increased capacity.
CDMA makes full use of the processing power of the modern computers CDMA allows a channel to carry multiple con-versations at the same time by assigning each conversation at different code. A code is a pattern of bits. The receiver looks for that bit pattern. So even if there are ten conversation in a particular channel at the particular instant of time, no calls interferes with another. As long as the receiving device has the right code, it can pick up its conversation but from all the others. Since CDMA spreads multiple conversations across a wide segment of spectrum, it is known as a Spread Spectrum Technology.
The Spread Spectrum uses two types of modulation schemes
Frequency Hopping Modulation : Frequency hopping rapidly switch among several predetermined frequencies. For this work, the transmission and receiver must be in nearly perfect synchronization. Bandwidth can increase by simultaneously transmitting on several frequencies.
Data sequencing modulation
It works by breaking the original data into parts (called chips), which are then transmitted on separate frequencies. The receiver can then isolate the chip and reassemble the data while ignoring the decory information.
The chipping code used in transmission is known only to the sending and receiving stations, making it difficult for intruder to intercept and decipher wireless data encoded in this manner.
Thus it provides following benefits:
CDMA reduce background noise and cross talk, ensuring better voice quality, which is further enhanced by the microprocessor inside the phones.
CDMA provides capacity for voice and data communications, allowing more subscribers to connect at any given time and makes it capable for multimedia task.
CDMA provides better spectral efficiency and consumes very little power leading to enhanced battery life and longer talk time.
Due to its design, it is more secure against eavesdropping.
CDMA phones due to their low-power requirements can do with smaller-sized batteries, which decreases the overall weight of a CDMA phone.
Calling capacity is superior due to better spectral efficiency
Difference between TDM and CDMA
GSM is based on Time Division Multiplexing and is very different form of Direct Sequence spread spectrum used by CDMA. To understand the difference between GSM and CDMA consider a large gathering in a hall with GSM people are allowed to talk one by one; each have a time slot for communication one after the other. CDMA gives more out of this. It allows each couple to talk at the same time but in different language because in this code is divided, not the time, hence neither creating problem of cross talk nor the background noise. This helps in extracting the desired signal while rejecting everything else treated as noise.
Viewing the technical aspects, the differences between the two standards: TDM users take turns sharing the frequency in a round-robin fashion with each one periodically getting the entire bandwidth for a little burst.
Thus, each user get a times lot on which to send and receive data. On the other hand spread spectrum uses the same frequency for several users simultaneously with minimal interference and use noise like carrier weaves that provides larger bandwidth.
The Road Ahead
Involvement of India's foremost Corporate families and large scale advertising created a lot of confusion regarding selection of standard among users. So we point some consideration which may prove out to be useful for making the right choice before selecting a standard.
GSM is mature, having started in the mid-80s. This maturity means a more stable network with robust features. GSM is already used worldwide. CDMA is still building its network.
GSM supports International roaming which permits subscribers to stay in touch wherever you go within your city, across the country or around the globe-on a single number. CDMA will work only within the Short Distance code Area (SDCA), which is typically city limits.
The availability of Subscriber Identity Modules (SIM), which are smart cards that provide secure data encryption give GSM m-commerce advantages.
GSM Voice clarity is less superior to CDMA.
GSM Talk time is lower than that of CDMA.
With a GSM service, you can upgrade your handset anytime you wish. You can be within reach wherever you go. You can conveniently change your tariff plan. You can easily switch from one service provider to the other (BSNL, Airtel, Hutch, Idea). With CDMA, none of the above can happen.
Due to different standards, GSM handsets cannot be used for CDMA. CDMA supporting handsets are different, and more expansive than GSM handsets.
Never before has the country seen such heavy action in the telephony arena.
CDMA technology is relatively new compared to GSM.
GSM Mobiles offer international roaming and a SIM Card for mobile commerce.
But CDMA offers more talk time and better voice quality, even though the handset costs more and there is no SIM Card with a regulation that denies the roaming facility to CDMA phones in India, which technology will emerge stronger? We will have to wait and see.
(Writer: Manish Maheshwari and Ravi Mohan Sharma)