Praise for Fundamentals of WiMAX

11.1 Methodology for Link-Level Simulation 369models the effect of multipath fading and adds other-cell/sector interference. The other-cellinterference in link-level simulations is modeled as filtered 5 AWGN.The multipath fading between each pair of transmit and receive antennae is modeled as a tapdelayline (see Section 3.2). The received signal at the ith receive antenna can thus be written asN t L k∑ ∑r i () t = h i, k ()x t k( t – τ l,k ) + z i ( t), (11.1)k = 1l = 1where k is the transmit antenna index, Nt is the total number of transmit antennas, x k (t) is the signaltransmitted from the kth antenna at time t, and z i (t) is the other-cell interference. Additionally,l is the multipath index, τ l,k is the delay of the lth path—relative to the first arriving path—fromthe kth antenna, and L k is the total number of multipath components as seen from kth antenna.For the simulation results presented in this chapter, we modeled the channel between eachpair of transmit and receive antennas as a SISO multipath channel. The ITU pedestrian andvehicular multipath channel profiles, as described in Section 12.1, are used because they areconsidered good representations of the urban and suburban macro-cellular environments. Thespatial channel model (SCM) [1] developed by 3GPP is also a good representative of the MIMOmultipath channel in macrocellular environments. In this chapter, however, link-level results forthe SCM are not presented, since most of the literature for link- and system-level performance ofcompetitive wireless technologies, such as 1xEV-DO and HSDPA, is available for ITU channelmodels. Thus, the ITU channel models provide a better data point for comparative analysis withsuch wireless technologies.The ITU channel models, unlike the SCM, do not model any correlation between the fadingwaveforms across the transmit and receive antennas; those models were developed primarily tomodel SISO channels. Because the spacing between the various antenna elements at the transmitterand the receiver are of an order of a few wavelengths, in a wireless channel with a finitenumber of scatterers the fading waveforms across the antenna elements are expected to be correlated.In order to incorporate the effect of such correlation, we first generate the MIMO multipathchannel between the various pairs of transmit and receive antennas independently, withoutcorrelation. Then correlation is added, using coloring matrices Q t and Q r for transmit andreceive ends, respectively:H l t = Q r H' l tQH tQ r QH r = R rQ t QH t =R t(11.2)where H l (t) and H'(t) are the correlated and uncorrelated MIMO channel matrix for the lth path,respectively, at time t. The spatial-correlation matrices R t and R r capture the correlation between5. The transmitter pulse-shaping filter is used to generate the filtered AWGN for modeling other-cellinterference. In system-level simulations, as discussed in Chapter 12, other-cell interference ismodeled as an OFDM signal.