Multi-Carrier and Spread Spectrum Systems: From OFDM and MC ...

Multi-Carrier Spread Spectrum 47Rule:(C)(C, C)(C, −C)SF = 1 SF = 2 SF = 3 SF = 4(1)(1, 1)(1, 1, 1, 1)(1, 1, −1, −1)(1, 1, 1, 1, 1, 1, 1, 1)(1, 1, 1, 1, −1, −1, −1, −1)(1, 1, −1, −1, 1, 1, −1, −1)(1, 1, −1, −1, −1, −1, 1, 1)(1, −1)(1, −1, 1, −1)(1, −1, 1, −1, 1, −1, 1, −1)(1, −1, 1, −1, −1, 1, −1, 1)(1, −1, −1, 1)(1, −1, −1, 1, 1, −1, −1, 1)(1, −1, −1, 1, −1, 1, 1, −1)Figure 1-17Variable length orthogonal spreading code generationTable 1-15Radio link parameters of HSPAParameterBandwidthDuplex schemeMultiplexingModulationChannel codingData ratesHSPA (HSDPA, HSUPA)5MHzFDDCDMA with TDMDownlink: QPSK, 16QAMUplink: BPSK, QPSKConvolutional Turbo codeDownlink: 14.4 MbpsUplink: 5.7 Mbps1.4.1 Principle of Various SchemesThe first realization is referred to as MC-CDMA, also known as OFDM-CDMA. Thesecond realization is termed as MC-DS-CDMA. In both schemes, the different usersshare the same bandwidth at the same time and separate the data by applying differentuser-specific spreading codes, i.e. the separation of the user signals is carried out inthe code domain. Moreover, both schemes apply multi-carrier modulation to reduce thesymbol rate and, thus, the amount of ISI per sub-channel. This ISI reduction is significantin spread spectrum systems where high chip rates occur.The difference between MC-CDMA and MC-DS-CMDA is the allocation of the chipsto the sub-channels and OFDM symbols. This difference is illustrated in Figures 1-18and 1-19. The principle of MC-CDMA is to map the chips of a spread data symbol infrequency direction over several parallel sub-channels while MC-DS-CDMA maps thechips of a spread data symbol in the time direction over several multi-carrier symbols.