The Federal Trade Commission has given the green light to the acquisition of Trammell Crow by CB Richard Ellis Group Inc., Trammell Crow Co. said today. The FTC approved a shortened waiting period required under antitrust law. The deal, for about $1.8 billion, is expected to close next month. It is subject to the approval of Trammell Crow shareholders. CB announced in October that it planned to acquire the Dallas-based real estate company.