Orthogonal frequency division multiplexing using subsymbol processing (original) (raw)

Description BACKGROUND OF THE INVENTION Field of the Invention [0001] The present invention relates to signal processing, and more specifically to orthogonal frequency division multiplexing techniques used in signal transmission and reception: Description of the Related Art [0002] Orthogonal frequency division multiplexing (OFDM) is a signal processing technology well known in the field of communications. In general, OFDM operates by dividing a frequency spectrum into smaller subbands (a.k.a. subcarriers) and modulating these sub carriers with data symbols. [0003] FIG. 1 shows a simplified block diagram of one implementation of a prior-art OFDM transmitter 100. Transmitter 100 receives digital input data and converts the data into analog OFDM signals for transmission. Conversion of the data occurs through sequential steps of data symbol mapping 102, inverse fast Fourier transform (IFFT) processing 104, cyclic prefix appending 106, digital-to-analog conversion (DAC) 108, and spectral shaping 110. [0004] Data symbol mapping block 102 receives binary bits of data, which are divided into groups of finite length. One or more data symbols a[n] are created for each group of bits, using any one of a number of modulation techniques commonly known in the art, such as differential quadrature phase-shift-keying (DQPSK) or quadrature amplitude modulation (QAM). The length of each group and thus the number of input data bits per data symbol is determined by the modulation technique employed. [0005] IFFT 104 subsequently applies each set of N data symbols a[n] to a set of N subcarriers, which are numbered from 0 to N-1, where one data symbol a[n] is paired with each subcarrier. The subcarriers employed by OFDM are arranged orthogonally to one another, so that each subcarrier can be distinguished without intersymbol interference. Each set k of N data symbol a[n] and subcarrier pairs is then converted by IFFT 104 from frequency-domain representations into a time-domain OFDM symbol S k , consisting of N samples S k [i], where i equals 0 to N-1. The discrete model for each OFDM symbol S k may be expressed by Equation (1) as follows:

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