【文章內(nèi)容簡(jiǎn)介】 h different cell sizes have been channel models define the statistics of the 5 discrete propagation overview of widely used discrete multipath channel models is given in the 207 [8]: The COST 207 channel models specify four outdoor macro cell propagation scenarios by continuous, exponentially decreasing delay power density of these power density spectra by discrete taps are given by using up to 12 for settings with 6 taps are listed in Table this table for several propagation environments the corresponding path delay and power profiles are terrain causes the longest classical Doppler spectrum with uniformly distributed angles of arrival of the paths can be used for all taps for , different Doppler spectra are defined for the individual taps in [8].The COST 207 channel models are based on channel measurements with a bandwidth of 8–10 MHz in the 900MHz band used for 2G systems such as 231 [9] and COST 259 [10]: These COST actions which are the continuation of COST 207 extend the channel characterization to DCS 1800, DECT, HIPERLAN and UMTS channels, taking into account macro, micro, and pico cell models with spatial resolution have been defined in COST spatial ponent is introduced by the definition of several clusters with local scatterers, which are located in a circle around the base types of channel models are macro cell type has cell 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 t