Method of bit allocation in a multicarrier symbol to achieve non-periodic frequency diversity
View Patent ↗In an orthogonal frequency division multiplex (OFDM) communication system, data bits are assigned to several carriers to create frequency redundancy in the transmitted waveform. Uniformly spaced carriers occupy the frequency band of the OFDM signal. Multipath nulls caused by reflections of the transmitted signal can occur at periodic frequency intervals, for example in a coaxial cable. A non-periodic pattern of bit allocation to carriers creates frequency diversity that is resistant to periodic multipath nulls existing in the communication channel.
1. An OFDM modulator for transmitting a binary data word in a symbol having frequency diversity comprising:
a ramp counter for producing a series of bin number values;
a look up table for mapping the bin number values to bit select values, the look up table comprising entries that produce an assignment of bits to carriers, the assignment resulting in bits being repeated over a selection of carriers that have a non-uniform, pseudorandom pattern for distribution over a set of available frequencies upon which the carriers are transmitted.
2. The OFDM modulator of claim 1 further comprising means for disabling I and Q carrier amplitudes for a particular carrier and zeroing the transmitted energy for that carrier.