Improvement of code rate in OFDM communication systems encoded by QAM complementary sequences

Abstract

Based on the description Q-type-2 of quadrature amplitude modulation (QAM) constellation and standard Golay-Davis-Jedwab (GDJ) quaternary complementary sequences (CSs), this paper presents a new family of QAM Golay complementary sequences (GCSs), and determines their family size. The proposed QAM GCSs includes the known QAM GCSs from Cases I–III constructions as a special case. It is worthy of mentioning that the family size of new sequences is fairly larger than the one of the known sequences so that the code rate of the code consisting of new sequences is improved, which therefrom results in the increase of number of sub-carriers in OFDM communication systems employing the resultant QAM GCSs. More clearly, in a 64-QAM OFDM communication system whose signals are encoded by QAM GCSs, the number of sub-carriers in this system is at most 16 when the known QAM GCSs from Cases I–III constructions are employed. However, such number can be increased up to 32 when the proposed QAM GCSs are used. Finally, it should be pointed out that the peak envelope power (PEP) upper bounds, educed from the usage of both new and known QAM GCSs in an OFDM communication system, are the same.