Optimize inter-processor communication in dual baseband dual mode handsets

By Ming Hoong Chong, Cypress Semiconductor
March 03, 2008 --  mobilehandsetdesignline.com

With the onset of globalization, world travel today is prevalent be it for business or leisure; and with travel comes the process of planning to carry the basic essentials and gadgets for the trip. Today's mobile handsets, thankfully, make it redundant to carry such other gadgets as MP3 players, portable navigation devices, cameras and handheld video games. With more than 1 billion units shipped annually, a mobile handset is now one of the basic necessities that people cannot leave home without. However, the phone is not of much use when it does not work in the destination country.

For example, Japan and Korea support a different standard (CDMA and FOMA) than most of Europe, which only supports GSM. Many other countries support both standards (GSM and CDMA) and it depends on the carrier subscribed to. A single handset, therefore, cannot be used worldwide. Many travelers carry two phones or buy a new Subscriber Identification Module (SIM) card at the airport whenever they are on travel, emailing the new number to their friends and colleagues.

This disconnect has given rise to Dual Baseband Dual Mode (DBDM) handsets that promise true operability worldwide as handset manufacturers compete to provide their users with the desired "global" roaming ability. A DBDM handset is a single handset that has 2 separate baseband processors. These handsets usually contain 2 slots for inserting a SIM card for use with GSM channels and Removable User Identification Module (RUIM) for use with CDMA channels. Phones that already have CDMA capabilities on board, however, might only provide one slot for inserting a GSM SIM card. Current major handset manufacturers that tout "World Phones" include Research In Motion (RIM), Samsung, LG, Motorola, and others.

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