An improved multicarrier modulation system and method, which has the advantages of both isotropic orthogonal transfer algorithm orthogonal frequency division multiplexing (IOTA OFDM) and scalable advanced modulation (SAM), is introduced. The invention is root raised cosine (RRC) OFDM using the most spectrally efficient RRC filter without sacrificing the compact subchannel spacing of OFDM. The invention further provides an adjacent channel interference (ACI) suppression scheme and a modified RRC for better suppressing ACI of RRC OFDM. The ACI suppression scheme can also be applied to SAM with the modified RRC and to IOTA OFDM with a modified IOTA. The invention greatly improves a major problem of conventional OFDM namely ACI due to the use of a wide subchannel filter. Thus, the invention allows OFDM to meet even the strictest ACI requirements, which was not possible by using a conventional raised cosine windowing method.

A method for reducing a peak-to-average power ratio (PAPR) in an orthogonal frequency division multiplexing (OFDM) communication system including N carriers, among which L carriers are allocated to L reserved tones and data are carried by (N-L) remaining tones, wherein L is smaller than N, including generating an impulse signal from the L reserved tones; converting a phase of the generated impulse signal into a phase of a signal having a maximum peak value from among complex output signals obtained though inverse fast Fourier transform (IFFT) of the N carriers; scaling the generated impulse signal by the difference between the maximum peak value and a target power value; and complex-adding the scaled signal and the complex output signal after IFFT.

Channel fluctuation estimating section 101 estimates fluctuation amount of the channel between transmitting apparatus 100 and receiving apparatus 200, and carrier number determining section 102 determines the number of subcarriers used in transmission of signal based on channel fluctuation amount. That is to say, in the case of a remarkably rapid channel fluctuation caused by fast fading, etc., carrier number determining section 102 deduces relatively the channel fluctuation between symbols or within a burst, by decreasing the subcarriers number and increasing symbol rate per one subcarrier.

An improved multicarrier modulation system and method is introduced which has the advantages of both isotropic orthogonal transfer algorithm orthogonal frequency division multiplexing (IOTA OFDM) and scalable advanced modulation (SAM). The invention reduces adjacent channel interference (ACI) in the multicarrier modulation system used in multicast systems by generating (2601) a spectrally efficient modified pulse for multicarrier modulation and then adapting (2605) the pulse at the edge of the subchannel for reducing the ACI product by the total multicarrier signal (2607). This BTRRC OFDM (2607) is an Offset OFDM with BTRRC pulse (2605) while the prior art RRC OFDM (604) is an Offset OFDM with RRC pulse (603). BTRRC OFDM has characteristics similar to RRC OFDM and has better power efficiency in simulcast or Nakagami fading environments where there is a timing error. Thus, BTRRC OFDM is desirable to substitute SAM in a simulcast environment.

A constellation mapping apparatus, which can reduce the storage capacity of a memory to one fourth by only storing constellation points in one quadrant of each constellation map rather than storing all the constellation points in each of the constellation maps, is provided. The constellation mapping apparatus includes a memory, an address generation block, a complementation logic block, and a scaling block. In the memory, constellation values in one of four quadrants of each constellation. The address generation block receives constellation point data, bits-per-symbol information, and valid symbol information indicating whether or not the bits-per-symbol information is valid, and generates address information of the memory where the constellation values corresponding to the constellation point data are stored and quadrant information indicating a quadrant where the constellation point data are placed. Based on the quadrant information for the constellation point data, the complementation logic block complements or does not complement the constellation values read from the memory following the address information. The scaling block outputs an output of the complementation logic block or a value obtained by multiplying the output of the complementation logic block by a predetermined gain obtained based on a baud rate, which indicates a speed of transmitting the bits-per-symbol information.