Abstract-This paper presents a model for the scattering of radiowaves from the canopy of a single tree. The canopy is modeled as a cylindrical volume containing randomly distributed and oriented cylinders, representing the branches, and thin disks, representing the leaves. A simple expression for the incoherent scattered field outside the canopy is obtained using Twersky's multiple scattering theory. This expression is shown to agree well with results of scattering measurements on a live tree typical of those found in urban environments. The scattering model can be readily incorporated in ray-based propagation prediction tools that assist the planning of microcellular radio networks. This involves the use of so-called tree-scattered rays, which interact at the tree centers. Path loss predictions generated with the aid of the new model are shown and compared with measured data to illustrate the considerable improvement in prediction accuracy that can be achieved in realistic urban microcellular scenarios by taking into account the scatter from trees.

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This paper presents a reduced-complexity detection scheme, called iterative tree search (ITS) detection, with application in iterative receivers for multiple-input multiple-output (MIMO) wireless communication systems. In contrast to the optimum maximum a posteriori (MAP) detector, which performs an exhaustive search over the complete set of possible transmitted symbol vectors, the aim of the new scheme is to evaluate only the symbol vectors that contribute significantly to the soft output of the detector. To this end, a list of "good" candidate symbol vectors is generated prior to the actual computation of the detector output, with the aid of a sequential tree searching scheme based on the M-algorithm. For high-order QAM modulation formats, the complexity of the ITS detector can be further reduced with the aid of a special type of bit mapping called multi-level mapping. This results in a complexity per bit that is linear in the number of transmit antennas and roughly independent of the modulation order. Results from computer simulations are presented which demonstrate the good performance of the new scheme over a quasi-static Rayleigh fading channel, even for relatively small list sizes.

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