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Third Generation (3G) mobile communication technologies likeCDMA2000, WCDMA are already in deployment in many countries andTD-SCDMA will soon be deployed in China in addition with other technologies.These are changing the way we communicate, conduct business, accessinformation, and being entertained over the multimedia super highway. 3Gservices enable users to make video calls to the office and surf the netsimultaneously, or play interactive game wherever they may be.Althoughbandwidth of current 3G technologies promise burst rates up to 384Kb/s and2Mb/s for vehicular and indoor applications respectively, the averagethroughput per user is not expected to be more than 171 Kb/s during the peakhours. This bandwidth is adequate to meet the needs for voice, basic datacommunication and wireless Internet access, but not enough for newinteractive multimedia services such as mufti-parity video conference.As suchthere is demand to develop a new physical layer that can give higherbandwidth.These future networks have been termed NGN (Next GenerationNetworks).The main features of such a system will be greater capacity andaccess speed in the downlink.The vision of NGN wireless/mobile systems will be the provision of broadband access, seamless global roaming, andInternet/data/voice everywhere, utilizing for each the most appropriate alwaysconnected technology.
Multi-Carrier Code Division Multiple Access (MC-CDMA) is a promisingcandidate for the air interface of NGN wireless networks.MC-CDMA isessential扮an Orthogonal Frequency Division Multiplexing (OFDM) techniquewhere the individual data symbols are spread using a spreading code in thefrequency domain.The spreading code associated with MC-CDMA provides amultiple access technique as well as interterence suppression.It is veryefficient in spectrum usage and it is very effective in spectrum selectivechannel.The NGN networks are predicted to provide packet data transmissionrates of 5Mbps in outdoor-macro-cellular environments and up 20Mbps inindoor-micro-cellular environments.
In MC-CDMA systems, a number of sub carriers per user are used for thehigh-rate data transmission, and each data modulated by a different subcarrier is transmitted through a different frequency band.Each data undergoesa different channel condition and arrives with a different error rate at the basestation.By transmitting message data through all the sub channels based on the Channel State Information (CSI), a new data transmission scheme called"Dynamic Bit Allocation Multicarrier Code Division Multiple Access for NextGeneration Networksn is introduced in this dissertation. In this system, theCSI is assumed to be known to the transmitter.Then the base station transmitsthe data based on the CSI by using the principle of dynamic bit allocation.Simulated results have shown that adaptive MC-CDMA yields a higher systemcapacity than a conventional MC-CDMA.