GSM Vs CDMA - A Comparative Study

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Working of CDMA

CDMA works by converting speech signals into digital signals, which are then transmitted over a wireless network and then decoded at the receiver's end. The receiver's equipment, is tuned to identify the particular code. A unique code is used by the equipment to distinguish every call from others. CDMA allows many users to share the airwaves without any cross-talk or interference. Hence, several calls can be made at any given time on the same frequency. GSM Vs CDMA CDMA uses a technology called Wireless in Local Loop (WLL) (Refer Exhibit-II). The limited mobility25 offered by CDMA is best suited for users who want cheaper services. Users who generally travel a lot tend to prefer GSM phones. Since GSM has been around for a long time, it has struck more than 60 roaming agreements worldwide. GSM service providers thus give complete freedom to their users to use their phones in any country of the world across the globe.

This is indeed the unique selling proposition of GSM phones. But since the majority of the world's population does not travel great distances, this feature might not make a huge difference to them.

GSM users can access several value added services like SMS and web browsing through their phones. In CDMA, in India, the legality of SMSing is still an issue. Some CDMA providers offer SMS services from CDMA to CDMA, but not from CDMA to GSM. In India WLL providers are not allowed to offer such services.

By April 2003, 70.4% of the world's mobile users went for GSM while only 13.1% chose CDMA (Refer Exhibit III). So GSM is still the more popular technology. CDMA is a relatively new and developing technology and hence a solution to the technical problems of CDMA might be attained very soon. CDMA companies are of the opinion that their technology will dominate in the market in the years to come. But the supporters of GSM argue that since GSM is strongly rooted in the mobile market, replacing it would be difficult.

Comparison of Handsets

CDMA poses a threat to GSM. It makes full use of the limited bandwidth by squeezing in several calls. So handsets that use CDMA technology are smaller and slicker, have better voice and data quality.

There are two main reasons for the difference in handsets. GSM operates on 900 MHz and 1800MHz bands and CDMA works on 800MHz band. Besides this, the cell size for CDMA has a radius of around 50kms while GSM uses a cell size of 30 kms. CDMA requires fewer cells than GSM to cover a certain area, thus eliminating the need to have bigger handsets.

But CDMA handsets also have certain drawbacks. The CDMA user is stuck with one WLL service provider because his handset is programmed to work with that particular service provider who sells it to him. A CDMA handset does not have a SIM card. If the user's handset is stolen, lost or damaged, he has to procure a new handset and then reprogram it. This is an expensive and time-consuming procedure. The same process has to be carried out if he wants to upgrade or change his handset. If the user wants to change networks he has to get the entire handset reset or reprogrammed. So a CDMA handset is said to be locked to the network it is initiated on. This is why CDMA operators generally provide a handset along with the service. A GSM phone does not have these disadvantages as it uses a SIM card. So if a user likes a different handset, he can buy it and reprogram it all in a matter of minutes.

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25] Uses a technique by which a signal transmitted hops among several frequencies at a specified rate and sequence as a way of avoiding interference.

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