Patent ID: 7808882

Claim:
A method for transmitting a reference signal in a wireless communications network that uses orthogonal frequency division multiplexing (OFDM) and includes a plurality of base stations and a plurality of transmit/receive terminals, a base station having multiple antennas and transmitting to a terminal a downlink reference signal comprising a plurality of reference symbols in resource blocks, a resource block comprising a plurality of OFDM subcarriers and a plurality of OFDM symbols in time slots of a radio frame, a radio frame comprising a plurality of subframes, the method comprising: transmitting at least two subframe reference symbol (RS) structures within a radio frame, a first subframe RS structure representing a first set of antennas and transmitted in a plurality of radio subframes and a second subframe RS structure representing a second set of four antennas (4-TX) in a multiple-input multiple-output (MIMO) system and transmitted in at least one radio subframe; prior to transmitting, determining the radio subframe in which to transmit said second subframe RS structure; and in response to an increase in the number of 4-TX capable terminals transmitting to the base station, increasing the number of radio subframes in which to transmit said second subframe RS structure.