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

Software-Defined Radio 3310.10.011TxCDDSPCEGTMRT0.001BER0.000110 −510 −60 4 8 12 16SNR in dBFigure 6-33 BER versus SNR for OFDM-CDM with CDD, SPC, EGT, and MRT: COST 207TU channel, fully loaded, R = 2/3, QPSK, = 0.4The performance of OFDM-CDM with CDD, SPC, EGT, and MRT is shown inFigure 6-33. The system is fully loaded. The results show that CDD achieves a significantperformance improvement of about 3 dB at a BER of 10 −5 compared to the 1Txscheme. Further investigations on OFDM-CDM with spatial diversity can be found inReference [19].6.5 Software-Defined RadioThe transmission rate for future wireless systems may vary from low rate messages upto very high rate data services up to 1 Gbit/s. The communication channel may changein terms of its grade of mobility, the cellular infrastructure, the required symmetrical orasymmetrical transmission capacity, and whether it is indoor or outdoor. Hence, air interfaceswith high flexibility are required in order to maximize the area spectrum efficiencyin a variety of communication environments. Future systems are also expected to supportvarious types of services based on the IP protocol, which require a varying quality ofservices (QoS).Recent advances in digital technology enable the faster introduction of new standardsthat benefit from the most advanced physical (PHY) and data link control (DLC) layers(see Table 6-3). These trends are still growing and new standards or their enhancementsare being added continuously to the existing network infrastructures. As explained in