Channel probing signal for a broadband communication system

Abstract

In a broadband wireless communication system, a spread spectrum signal is intentionally overlapped with an OFDM signal, in a time domain, a frequency domain, or both. The OFDM signal, which inherently has a high spectral efficiency, is used for carrying broadband data or control information. The spread spectrum signal, which is designed to have a high spread gain for overcoming severe interference, is used for facilitating system functions such as initial random access, channel probing, or short messaging. Methods and techniques are devised to ensure that the mutual interference between the overlapped signals is minimized to have insignificant impact on either signal and that both signals are detectable with expected performance by a receiver.

What is claimed is: 
     
         1 . A receiving device for operating in an orthogonal frequency division multiple access (OFDMA) communication system, the OFDMA system having a system bandwidth with a plurality of subcarriers, the OFDMA system dividing the system bandwidth into groups of subcarriers in a frequency domain and time intervals in a time domain for communication, each time interval including a plurality of OFDM symbols, the receiving device comprising:
 a receiver configured to receive a transmission, from a transmitting device, in at least one of the groups of subcarriers and one of the time intervals, wherein the received transmission includes data received on first subcarriers of the at least one of the groups of subcarriers, at least one pilot received on at least one of second subcarriers of the at least one of the groups of subcarriers and a signal received on third subcarriers of the at least one of the groups of subcarriers, wherein the signal received on the third subcarriers is used for channel estimation and has a lower transmission rate than a transmission rate of the data received on the first subcarriers, wherein the signal received on the third subcarriers is received at a lower power level than the at least one pilot received on the at least one of the second subcarriers in a same OFDM symbol of the plurality of OFDM symbols, and wherein the data and the at least one pilot occupy non-overlapping subcarriers in a same OFDM symbol of the plurality of OFDM symbols; and   a processing circuitry configured to recover data from at least the first subcarriers.