WiMAX does possess NLOS capabilities, although how much and to what extent will vary depending on the spectrum bands being used.  Non line of sight indicates that the signal from a radio is received by either passing through impeding objects, such as tree tops, walls or even in some cases buildings or is received as a reflection from another building, body of water or land feature.  In both cases the broadcasting radio is completely or at least partially obscured by some obstruction. 

WiMAX radios utilize many of the best current techniques for receiving reflected signals from objects (such reflected signals are called multipath).  Some of these incorporate antenna diversity techniques.  The OFDM modulation favored by the first iteration of WiMAX actually takes advantage of reflected signals allowing radios to integrate multiple reflected signals to improve signal strength and accuracy.  The Mobile WiMAX technique of OFDMA® also advantageously integrates both in phase (or directly returned signal responses) and out of phase multipath signals (reflections of returned signals that bounce from other objects---resulting in their returning slower) to create an ultimately stronger signal. 

Additionally, for WiMAX radios that are built for service in licensed bands (currently 2.5 GHz in the US and 2.5 GHz and 3.5 GHz Internationally - although other licensed spectrums below 11 GHz will be used in other profiles in future) the additional power allowed in these bands (typically around 40 Watts) permit signal to actually penetrate through some tree cover and building walls.  There are limits posed by the physics of the spectrum range in question and power allotted.  In general NLOS ranges in the 2.5 GHz band will mostly fall between 6-8 Kilometers (4-5 Miles).  Expect additional technology to follow in coming years.  The innovation curve for WiMAX should continue to be very steep. 

In 2005 support for both Adaptive Antenna Systems sometimes called multiple input multiple output (MIMO) and beamforming antenna techniques were added to the mobile WiMAX standard.  Both technologies will be incorporated in Mobile WiMAX technology.  and significantly improves gain and thus signal strength and reliability for users.  Competing camps tout the various approaches and which is best is open to interpretation and probably the specifics of the application desired.  Navini is a company, now owned by Cisco, championing beamforming while ArrayComm's technology would be one expected to be widely used with AAS/MIMO systems.  Currently Mobile WiMAX technology is heavily invested with companies using MIMO and some type of AAS.  As the first Clearwire mobile systems come online (the company is testing its first markets now as is Sprint) they will incorporate this technology.