Smart antennas for UTRA TDD

Abstract

Abstract. Due to the increasing number of users in mobile communications and the demand for mobile multimedia services with high data rates, third generation mobile radio systems are currently one ofthe key communication technologies in research, development, and international standardization bodies. Smart antennas can be used to increase thc capacity of wireless communication systems even further. TDD systems are particularly attractive for the employment of smart antennas, since the channel information (e.g.. in terms of spatial covariance matrices) estimated on the uplink can be used directly for downlink beamforming. In this paper, we discuss efficient uplink and downlink processing techniques with smart antennas for UTRA TDD, the TDD mode of third generation mobile radio systems that is based on TD-CDMA. On the uplink, joint space-time processing is used to eliminate cochannel interference created by other users that transmit on the same frequency and in the same time slot. These joint detection techniques are efficiently implemented in the frequency domain. On the downlink, the data is only tnnsmitted in the direction of the desired mobile user while interference in the direction of cochannel users is avoided. Moreover, short-rerm spatial channel estimates can be improved by projecting them into the dominant subspace of the long-term spatial covariance matrix. System level simulations have been performed to evaluate the gain in spectral efficiency (available bit rate per bandwidth per cell) if simple downlink beamforming techniques are used at the base stations. There is a two-to three-fold spectral efficiency gain if antenna arrays of . \ I = 8 elements are deployed in a sectorized macro-cellular environment.

Eigenbeam transmission over line-of-sight MIMO channels for fixed microwave links

“…is essentially identical to the eigendecomposition, given in (15) and (16). In addition, we can exploit the Kronecker product,…”

“…This derivation closely follows [15,Appendix]. It is assumed that the ground reflection geometry is planar, i.e., the spread in azimuth shall be negligible compared to the spread in elevation ϑ.…”

“…zero mean circularly complex Gaussian random elements (Rayleigh fading). The matrices R and T are calculated from the power distribution of the ground reflection versus elevation angle ϑ by assuming uncorrelated scattering [15,Eqs. (23) and (24)].…”