• Journal of the Korean Institute of Telematics and Electronics S
• /
• v.36S no.11
• /
• pp.1-8
• /
• 1999

In this paper, new polyphase sequences and a sequence generation method are suggested. These sequences are found to have good correlation properties. Since the suggested generation method consists only of integer sums and modular techniques, sequence generation is also easy. The performance of the sequences is investigated when used in QS-CDMA systems under frequency selective, time nonselective, slow Nakagami fading channel with additive white Gaussian noise.

• Journal of the Institute of Electronics and Information Engineers
• /
• v.50 no.11
• /
• pp.21-27
• /
• 2013

This paper proposes an adaptive modulation based incremental hop selection scheme which improves network coverage in half-duplex multi-hop networks. The proposed scheme guarantees wide coverage through the operation of multi-hop network while preventing spectral efficiency loss due to the usage of multiple time phases in the half-duplex protocol. Also, we evaluate the average spectral efficiency performance over Nakagami-m fading channel. The simulation results show that the proposed scheme outperforms the existing schemes and the derived evaluation is valid.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.10 no.7
• /
• pp.1118-1130
• /
• 1999

In this paper, error performance of DS/FH CDMA system has been analyzed in a radio channel which is characterized by near-far problem and multi-path fading. The DS/FH CDMA system adopts Maximum Ratio Combining(MRC) diversity and BCH(Bose-Chau dhuri-Hocquenghem) coding techniques to enhance system performance. Using the derived error probability equation, the error performance of DS/FH CDMA system has been evaluated and shown in figures to discuss as a function of PN code length(N), hopping rate(q), number of diversity branch(M), coding rate($\gamma$) and bit energy per noise power ratio ${E_b/N_o}$. The results show that DS/FH system is more effective to restrain the affection of near-far problem and multi-path fading than DS system. And there is a substantial enhancement in performance by employing an MRC diversity or BCH coding techniques. Consequently, we expected that proposed system structure is reliable to the voice communication system in near-far problem and multi-path fading channel.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.5A
• /
• pp.401-407
• /
• 2009

The multi-band (MB) ultra-wideband (UWB) communication system divides its available frequency spectrum in 3.1 to 10.6GHz into 16 sub-bands, which leads to inherent disparities between carrier frequencies of each sub-band. For instance, the highest carrier frequency is 2.65 times higher than the lowest one. Since the propagation loss is proportional to the square of the transmission frequency, the propagation loss on the sub-band having the highest carrier frequency is approximately 7 times larger than that on the sub-band having the lowest carrier frequency, which results in disparities between received signal powers on each sub-band. In this paper, we propose a novel correlation scheme for frequency hopping (FH) MB UWB communications, where the correlation time is adaptively adjusted relative to the sub-band, which reduces the disparity between the received signal energies on each sub-band. Such compensation for lower received powers on sub-bands having higher carrier frequency leads to an improvement on the total average bit error rate (BER) of the entire FH MB UWB communication system. We analyze the performance of the proposed correlation scheme in Nakagami fading channels, and it is shown that the performance gain provided by the proposed correlator is more significant as the Nakagami fading index n increases (i.e., better channel conditions).