The next-generation mobile communication system aims to realize a high-speed data transmission of 100Mbps or faster for downstream. NTT DoCoMo plans to develop the prototype by this summer for access testing.

Discussions have been held on the fourth-generation mobile communications system, to be commercialized in 2010, at the WP8F, a working group of International Telecommunications Union-Radiocommunication Sector (ITU-R.)

NTT DoCoMo aims to secure a leading position in development of the next-generation mobile communications system by proposing a new data transmission method for the system earlier than its rivals.

In an attempt to realize the high-speed data transmission of 100Mbps or faster, the mobile telecom giant is developing a new wireless access method called VSF (variable spreading factor)-OFCDM (orthogonal frequency and code division multiplexing), CDMA spreading factor based on OFDM (orthogonal frequency division multiplexing) for wireless local area networks (LANs) at 5GHz.

VSF-OFCDM is a type of a multi-carrier CDMA technology called MC-CDMA. As with OFDM, VSF-OFCDM employs dense sub carriers to use the frequency more effectively, and it is not affected by multipath interference. Use of spreading factor, as with CDMA, will enable VSF-OFCDM to use the same frequency as adjacent cells.

VSF-OFCDM can be employed both for services for specific areas such as hot spots and for wide-range areas utilized services as cellular phone by adopting variable spreading factor.

According to NTT DoCoMo, the new system to be proposed by the company can realize the data transmission speed of 103.68Mbps by using QPSK for the primary modulation method at 100MHz. The speed will be increased to 331.776Mbps by using 64-QAM for the primary modulation method and 1 for the coefficient of spreading factor. OFDM will have 768 sub carriers and symbol length of 9.952 micro seconds. It will use turbo encoding, NTT DoCoMo said.