In this letter, a 2-D Direction-of-Arrival (DoA) estimation scheme with cell searching is proposed for a mobile relay station (MRS) with uniform circular array (UCA) at a handover region. The proposed scheme of cell searching and DoA estimation for the MRS with UCA is robust even when there exist symbol timing offsets (STOs). Compared with the previous scheme, the proposed scheme can reduce computational complexity and processing time for cell searching and DoA estimation. Simulation results are included to verify the performance of the proposed scheme under a mobile WiMAX environment.

In this paper, a Direction-of-Arrival (DoA) estimation scheme with cell searching is proposed for a mobile relay station (MRS) with uniform circular array (UCA) at handover region. The proposed scheme of cell searching and DoA estimation for the MRS with UCA is robust even when there exist symbol timing offsets (STOs). Compared with the previous scheme, the proposed scheme can reduce computational complexity and processing time for cell searching and DoA estimation. Simulation results are included to verify the performance of the proposed scheme under Mobile WiMAX environment.

In this paper, we propose a new digital duplexing scheme, called synchronous digital duplexing (SDD), which can increase data efficiency and flexibility of resource by transmitting uplink signal and downlink signal simultaneously in wireless communication. In order to transmit uplink and downlink signals simultaneously, the proposed SDD obtains mutual information among subscriber stations (SSs) with a mutual ranging symbol. This information is used for selection of transmission time, decision on cyclic suffix (CS) insertion, determination of CS length, and re-establishment of FFT starting point. It is shown that in terms of efficiency and flexibility the proposed SDD is better equipped as a duplexing scheme for indoor wireless environments than conventional time division duplexing (TDD) and frequency division duplexing (FDD).

In this paper, a mobile relay station (MRS) for vehicles with beamforming antennas is considered to increase the reliability of transmission link, especially for the MRS at cell boundary. Joint methods for cell searching and DoA estimation are proposed to form a beam in the direction of target BS while nulling interferences from adjacent BSs, especially for IP- based cellular systems employing break-before-make handover or make-before-break handover. The proposed cell searching and DoA estimation methods are evaluated by computer simulation under the environment of IEEE 802.16e (WiBro).

In this paper, a new method of inter-cell interference (ICI) cancellation in the downlink is proposed for users at the cell boundary in OFDM-based cellular systems, by using the concept of a subcarrier-based virtual multiple-input multiple-output (SV- MIMO) where multiple antenna techniques are performed on a set of subcarriers, not on the actual antenna array. In the proposed SV-MIMO, "subcarrier signatures," obtained at the mobile station (MS) with a single antenna, are exploited to separate the desired signal from ICIs. The concept of a virtual signature randomizer (VSR) is introduced to improve channel separability in the SV-MIMO approach. Also, the concept of a virtual smart antenna, in which the steering vector is formed by a set of subcarriers with the estimated symbol timing offset (STO) between BSs, is compared with conventional ICI reduction methods. It is shown by simulation that the proposed method is effective in reducing ICI and inter-sector interference for fully- loaded OFDM cellular systems with a frequency reuse factor equal to 1, compared with conventional methods.