ABSTRACT
In this project, we propose a “two-level” frequency hopping code-division multiple-access (FH-CDMA) scheme for wireless communication systems. The new scheme provides flexibility in the selection of modulation codes and FH patterns. By partitioning the modulation codes, our two-level scheme can be modified to support more possible users without increasing the number of FH patterns. The performance and spectral efficiency (SE) of the scheme are analyzed. Our results show that the partitioned two-level FH-CDMA scheme supports higher data rate and greater SE than Goodman’s frequency-shift-keying FHCDMA scheme under some conditions.
INTRODUCTION
FREQUENCY-HOPPING code-division multiple access (FH-CDMA) provides frequency diversity and helps mitigate multipath fading and diversify interference. Major advantages of FH-CDMA over direct-sequence CDMA include better resistance to multiple access interference (MAI), less stringent power control, and reduced near-far problem and multipath interference. By assigning a unique FH pattern to each user, a FH-CDMA system allows multiple users to share the same transmission channel simultaneously. MAI occurs when more than one simultaneous users utilize the same carrier frequency in the same time slot. “One-hit” FH patterns have been designed in order to minimize MAI.
In addition, Goodman, proposed to add 𝑀-ary frequency-shift-keying (MFSK) atop FH-CDMA in order to increase data rate by transmitting symbols, instead of data bits. Furthermore, the uses of prime and Reed-Solomon (RS) sequences as modulation codes atop FH-CDMA were proposed in which the symbols were represented by non-orthogonal sequences, rather than orthogonal MFSK. These prime/FH-CDMA and RS/FH-CDMA schemes supported higher data rate than Goodman’s MFSK/FH-CDMAscheme at the expense of worsened performance. However, the weights and lengths of the modulation codes and FH patterns needed to be the same in both schemes, restricting the choice of suitable modulation codes and FH patterns to use.