GSM Vs CDMA - A Comparative Study

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Comparison of Handsets Contd...

Advantages of CDMA26 Higher capacity: CDMA allows a greater number of calls to be transmitted at a given point in time over the frequency spectrum than GSM. It thus provides higher traffic capacity. But this increase in capacity is accompanied by a reduction in voice quality. CDMA is therefore said to have "soft capacity." GSM's capacity, however, is fixed. CDMA’s capacity is 2 to 3 times more than that of GSM and 10 to 20 times more than that of analog equipment. Soft handoff reduces call drop rates: A handoff27 occurs in any cellular system when a user's phone switches from one cell site to another as he travels. Generally this handoff occurs when the network informs the phone of the cell site to which it must switch. The phone then stops receiving and transmitting on the old channel and commences transmitting and receiving on a new channel. This is called a ‘hard handoff.’

In CDMA, when a call is in progress, the network choses two or more cell sites which it considers favorable for a handoff. It then broadcasts a copy of the call to each of these sites. The phone can then choose between these sites and move to one of them. This facility ensures that the phone is in complete control of the handover process and that there is always a site ready to take over a call at short notice. This technique is called ‘soft handoff.’ A soft handoff ensures that CDMA users experience very few dropped calls.

In GSM, the network informs the phone of the timing of the handoff and the system it must switch to. This leads to abrupt handovers and disconnection during transition. This disadvantage is particularly evident when the subscriber is mobile or is in an area with closely spaced cells.

Outstanding voice and call quality: CDMA filters out background noise, cross-talk and interference so that greater privacy, improved call quality and clear voice quality is obtained. It translates voice signals into digital transmissions at a high translation rate of 8kbps or 13kbps, and hence improves system capacity.

Reduced background noise: Electrical background noise (computer noise) and acoustic background noise (background conversations) are filtered out using a narrow bandwidth which corresponds to the frequency of the human voice.

Rapid deployment: CDMA systems can be deployed and expanded faster and more cost effectively than GSM systems. This is because they require fewer cell sites than other wireless networks as their cell sizes are large.

Low power requirements: CDMA handsets transmit at the lowest power levels in the industry. So their batteries have a longer life and can provide longer talk time and standby time. Since CDMA handsets use smaller batteries than GSM handsets, they are smaller and lighter. This makes them easy to carry and use.

Improved security and privacy: CDMA is designed with about 4.4 trillion codes. This makes CDMA a more secure system than GSM. Wide product selection: Qualcomm has licensed CDMA technology to over 65 leading communications manufacturers’ worldwide, enabling service providers and customers to choose from a wide range of highly advanced, cost-competitive, CDMA-based products.

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26] www.qualcomm.com.
27] The process of moving from one cell to another when a call is in progress. To perform a handoff, the base station of the cell the user is moving to should allocate a channel to the mobile unit. If no channel is available in the new cell, the handoff call is blocked.

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