Search

Byline: Ersin Ozturk (1), Umit Aygolu (2) Keywords: fading channels; interleaving; trellis codedmodulation; diversity; suboptimal decoder Abstract: Freedom of mobility is the latesttrend in the evolution of digital communicationsystems. In these systems bandwidth and powerconstraints limit the mobility of the users. TCM(trellis coded modulation) is a combined coding andmodulation scheme which increases the productivity ofa digital communication system without increasing thetransmitted power or the required bandwidth. A mobilecommunication channel is affected from noise andfading because of the multipath propagation. On aRayleigh fading channel, coding should be used withtechniques which uncorrelate the received energy ofeach consecutive coded symbol. Interleaving is one ofthese techniques and used to make burst errors intorandom errors which can be corrected by errorcorrecting codes. In this paper, the trellis codingsystem which combines a regular convolutional encoder,bit interleaver, coordinate interleaver, and anappropriate decoder is considered. The analytical biterror probability upper bounds are derived for the8-PSK TCM system whose diversity is increased by usinga regular 2/3 rate convolutional code followed bythree bit interleavers and a 8-PSK signal mapperfollowed by two coordinate interleavers. Theanalytical and simulation results show that toincrease the diversity of the trellis coded M-PSKsystems in Rayleigh fading channels is the primary keyfor reliable transmission of high quality voice anddigital data. Author Affiliation: (1) NETAS, Alemdag, Cad. 81244 Umraniye, Istanbul, Turkey (2) Faculty of Electrical-Electronics Eng., Istanbul Technical University, 80626, Maslak, Adegstanbul, Turkey Article History: Registration Date: 04/10/2004

In this paper, to improve bandwidth efficiency and error performance, partial response signaling (PRS) and trellis coded modulation (TCM) are combined together and named as QPR-TCM. Whereas previous contributions have considered the performance of TCM transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in this paper is on the performance of trellis coded MQAM combined with PRS in the fading environment. We shall only consider the case where interleaving/deinterleaving is employed to further combat the fading and assume that the ideal channel state information (CSI) is available. Analytical upper bounds are derived using the well known transfer function bounding technique, the bandwidth efficiencies are computed and the numerical results for several practical schemes are compared to each other. One interesting result is that when the combined system is used on a Rician fading channel, the bit error probability upper bounds of the proposed 6QPR-TCM and 9QPR-TCM systems are better than their counterparts the 4QAM-TCM systems with 2 and 4 states, respectively, for SNR values greater than a threshold, which have the best error performances in the literature.

The trellis coding technique is applied to line-coded baseband digital transmission systems. For R = n/n + 1(n = 1, 2, 3) coding rates, a new codeword assignment model is proposed to accomplish basic requirements for line coding in which each length n binary data sequence is encoded into a length n + 1 ternary (+, 0, -) line codeword chosen among the code alphabet with 2(super n+2) elements. Assuming Viterbi decoding, the system error performance is improved by increasing the free Euclidean distance between coded sequences. A new algorithm is given for the calculation of the free distance between line-coded sequences so obtained. For R = 1/2 and R = 3/4 rates, the analytical error performance upper bounds are derived. The power spectral densities of the new line codes are also calculated and compared with those of known line codes.

In this paper, we introduce multilevel coded continuous-phase frequency-shift keying (CPFSK) systems for both additive white Gaussian noise and fading channels based on multilevel coding and multistage decoding techniques. These schemes are designed under the constraint M [is greater than or equal to] 2P for M-ary CPFSK with modulation index J/P. In order to maintain the phase continuity property after multilevel coding, we use some specific set partitioning rules. We construct examples to show that the proposed systems outperform the corresponding conventional one-level schemes. Far the fading case, we consider an ideal fading channel where adjacent fading symbols are assumed to be independent and a correlated fading channel where bit interleavers are needed at each coding level. The computer simulation results show that the proposed systems have bit-error performance and decoder complexity advantages over the corresponding reference codes taken from the literature. It is also shown that there is only a slight degradation on the bit-error performance for correlated fading, compared to the ideal fading case. Index Terms--Continuous phase modulation, fading channels, multilevel coding.

In this paper, we introduce multilevel coded continuous-phase frequency-shift keying (CPFSK) systems for both additive white Gaussian noise and fading channels based on multilevel coding and multistage decoding techniques. These schemes are designed under the constraint M [is greater than or equal to] 2P for M-ary CPFSK with modulation index J/P. In order to maintain the phase continuity property after multilevel coding, we use some specific set partitioning rules. We construct examples to show that the proposed systems outperform the corresponding conventional one-level schemes. For the fading case, we consider an ideal fading channel where adjacent fading symbols are assumed to be independent and a correlated fading channel where bit interleavers are needed at each coding level. The computer simulation results show that the proposed systems have bit-error performance and decoder complexity advantages over the corresponding reference codes taken from the literature. It is also shown that there is only a slight degradation on the bit-error performance for correlated fading, compared to the ideal fading case.