【正文】 ell sizes from 500 m up to 5000 m and a carrier frequency of 900 MHz or micro cell type is defined for cell sizes of about 300 m and a carrier frequency of GHz or 5 pico cell type represents an indoor channel model with cell sizes smaller than 100 m in industrial buildings and in the order of 10 m in an carrier frequency is GHz or 24 273: The COST 273 action additionally takes multiantenna channel models into account, which are not covered by the previous COST [7]: These channel models define typical outdoor and indoor propagation scenarios for macro, micro, and pico fading characteristics of the various propagation environments are specified by the parameters of the Nakagamim environment is defined in terms of a number of scatterers which can take on values up to channel models consider also the angular distribution of the have been developed for the investigation of 3G system cell channel type models have been developed for carrier frequencies around 900 MHz with 7 MHz micro and pico cell channel type models have been developed for carrier frequencies between GHz and 2 bandwidths of the measurements are in the range of 10–100 MHz for macro cells and around 100 MHz for pico [28]: The JTC channel models define indoor and outdoor scenarios by specifying 3 to 10 discrete taps per channel models are designed to be applicable for wideband digital mobile radio systems anticipated as candidates for the PCS(Personal Communications Systems)mon air interface at carrier frequencies of about 2 [18][44]: Test propagation scenarios have been defined for UMTS and UTRA system proposals which are developed for frequencies around 2 modeling of the multipath propagation corresponds to that used by the COST 207 channel [33]: Five typical indoor propagation scenarios for wireless LANs in the 5 GHz frequency band have been scenario is described by 18discrete taps of the delay power density time variance of the channel(Doppler spread)is modeled by a classical Jake’s spectrum with a maximum terminal speed of 3 m/ channel models exist which are, for instance, given in [16]. Channel Modeling Multicarrier systems can either be simulated in the time domain or, more putationally efficient, in the frequency for the frequency domain implementation are the absence of ISI and ICI, the frequency nonselective fading per subcarrier, and the timeinvariance during one OFDM proper system design approximately fulfills these discrete channel transfer function adapted to multicarrier signals results inwhere the continuous channel transfer function H(f, t)is sampled in time at OFDM symbol rate s and in frequency at subcarrier spacing durations is the total OFDM symbol duration including the guard , a symbol transmitted onsubchannel n of the OFDM symbol i is multiplied by the resulting fading amplitude an,i and rotated by a random phase ?n, advantage of the frequency domain channel model is that the IFFT and FFT operation for OFDM and inverse OFDM can be avoided and the fading operation results in one plexvalued multiplication per discrete multipath channel models introduced in Section can directly be applied to().A further simplification of the channel modeling for multicarrier systems is given by using the socalled uncorrelated fading channel Fading Channel Models for MultiCarrier Systems These channel models are based on the assumption that the fading on adjacent data symbols after inverse OFDM and deinterleaving can be considered as uncorrelated [29].This assumption holds when, ., a frequency and time interleaver with sufficient interleaving depth is fading amplitude an,i is chosen from a distribution p(a)according to the considered cell type and the random phase ?n,I is uniformly distributed in the interval [0,2π].The resulting plexvalued channel fading coefficient is thus generated independently for each subcarrier and OFDM a propagation scenario in a macro cell without LOS, the fading amplitude an,i is generated by a Rayleigh distribution and the channel model is referred to as an uncorrelated Rayleigh fading smaller cells where often a dominant propagation ponent occurs, the fading amplitude is chosen from a Rice advantages of the uncorrelated fading channel models for multicarrier systems are their simple implementation in the frequency domain and the simple reproducibility of the simulation The coherence bandwidth of a mobile radio channel is the bandwidth over which the signal propagation characteristics are correlated and it can be approximated byThe channel is frequencyselective if the signal bandwidth B is larger than the coherence the other hand, if B is smaller than , the channel is frequency nonselective or coherence bandwidth of the channel is of importance for evaluating the performance of spreading and frequency interleaving techniques that try to exploit the inherent frequency diversity Df of the mobile radio the case of multicarrier transmission, frequency diversity is exploited if the separation of subcarriers transmitting the same information exceeds the coherence maximum achievable frequency diversity Df is given by the ratio between the signal bandwidth B and the coherence bandwidth，The coherence time of the channel is the duration over which the channel characteristics can be considered as timeinvariant and can be approximated byIf the duration of the transmitted symbol is larger than the coherence time, the channel is the other hand, if the symbol duration is smaller than , the channel is time nonselective during one symbol coherence time of the channel is of importance for evaluating the performance of coding and interleaving techniques that try to exploit the inherent time diversity DO of the mobile radio diversity can be exploited if the separation between time slots carrying the same information exceeds the coherence number of Ns successive time slots create a time frame of duration maximum time diversity Dt achievable in one ti