| Author | Park, Gi Ho |
| Call Number | AIT Thesis no.TC-98-01 |
| Subject(s) | Mobile communication systems
|
| Note | A thesis submitted in partial fulfillment of the requirement for the degree of Master of Engineering, School of Advanced Technologies |
| Publisher | Asian Institute of Technology |
| Abstract | Turbo codes are well known for their tremendous error correction capability near
Shannon's limit (Berrou et al., 1993). This performance is obtained by exploiting the
additional soft information besides channel information for the particular symbol. This soft
information becomes meaningful due to the presence of the interleaver between two recursive
systematic convolutional (RSC) codes and its corresponding soft in/soft out (SISO) decoder
module. The soft extrinsic information is extracted from all other received symbols except
present symbol. It increases reliability of transmitted bit at a time instant. It is necessary to
combine multilevel modulation with binary turbo coding for bandwidth efficiency because it
is proposed to deal with binary bits.
In this thesis, spectrally efficient multilevel modulation is associated with turbo codes
over multipath Rayleigh fading channels. It can be considered to some extent as " pragmatic
approach"(Goff et al., 1994) over multipath Rayleigh fading channel. It is the first attempt to
handle multilevel symbols over frequency selective channels using binary turbo decoder. The
approach is different from that of trellis coded modulation (TCM) or turbo-TCM (T-TCM) in
the sense that the channel coding technique and modulation are independent of each other. In
this thesis, QPSK and 8PSK with bandwidth efficiency of 1 and 1.5 (bit/s/Hz) respectively are
considered. Their performances are compared with those over A WGN.
Rayleigh fading channel is modeled as two equal strength paths for QPSK and 8PSK
and as three equal strength paths for BPSK. Time variant fading coefficients are assumed to
be known at the receiver.
Turbo code performance with different modulation schemes is compared and it shows
that performance of 8PSK over ISI is degraded by 3.4 dB compared with that of AWGN. It
achieves .a BER 10ยท
4 with 3 iterations at a signal to noise ratio (Ei/No) of 10.2 dB, with a
bandwidth efficiency of 1.5 (bits/s/Hz) in 8PSK modulation. Its performance is comparable to
that of T-TCM.
In summary, turbo coded multilevel scheme considered here is a very promising
scheme to replace T-TCM which is complex to be implemented and inflexible to the change
of modulation. It is very useful in the sense that it can handle multilevel modulation without
changing binary turbo decoder. |
| Year | 1998 |
| Type | Thesis |
| School | School of Advanced Technologies |
| Department | Other Field of Studies (No Department) |
| Academic Program/FoS | Telecommunications (TC) |
| Chairperson(s) | Rajatheva, Premanandana ; |
| Examination Committee(s) | Makelainen, Kimmo; Ahmed, Kazi .Mohiuddin; |
| Scholarship Donor(s) | Asian Institute of Technology Partial Scholarship; |
| Degree | Thesis (M.Eng.) - Asian Institute of Technology, 1998 |