3 research outputs found
The Proceedings of the Skylab Life Sciences Symposium, Volume 1
The three manned Skylab missions resulted in biomedical experiment data in the areas of neurophysiology, musculoskeletal physiology, biochemistry, hematology, cytology, cardiovascular and respiratory metabolic functions: as well as detailed test objectives involving crew health and environment procedures. Major emphasis was placed on results from the last mission, Skylab 4, which covered 84 days of in-flight data collection. Many new norms were defined for normal man living and operating in a unique environment. While man is quite adaptable to this unique environment, many of the changes observed in Skylab require additional research for future flights lasting very long periods of time such as a Mars mission requiring 18 months
Sequences With Low Correlation Over a Nonbinary Alphabet
Doctor์์ฌ๋ถ๊ท์น ์์ด(pseudorandom sequence)์ ๋์ญํ์ฐ(spread spectrum), ์คํธ๋ฆผ ์ํธ(stream cipher), ๋ ์ด๋ค ๋ ์ธ์ง(ranging), ์ฑ๋ ์ถ์ ๋ฐ ๋๊ธฐ ํ๋ ๋ฑ์ ๋น๋กฏํ ํต์ ์์คํ
๋ฐ ๋์งํธ ์ ํธ์ฒ๋ฆฌ ๋ถ์ผ์ ๋๋ฆฌ ์ฌ์ฉ๋๊ณ ์๋ค. ํนํ ๋ค์ค ์ฌ์ฉ์ ์ ์์ ์ํ ๋์ญ ํ์ฐ ์์ด(spreading sequence)์ ๋์ญ ํ์ฐ ํต์ ๊ธฐ์ ์ ๋ฐํ์ผ๋ก ๊ตฌํ๋๋ ํต์ ์์คํ
๋ค์ ํต์ฌ ์์๋ผ ํ ์ ์๋ค. ๋ณธ ํ์๋
ผ๋ฌธ์์๋ ํฌ๊ฒ ๋ ๊ฐ์ง ๊ด์ ์ ๋ฐ๋ฅธ ์ง ์ํ๋ฒณ ์์ ๋ฎ์ ์๊ด ์์ด์ ๊ดํ ์ฐ๊ตฌ ๊ฒฐ๊ณผ๋ค์ ์ ๋ฆฌํ๊ณ ์๋ก์ด ์์ด๊ตฐ์ ์ค๊ณํ๋ค. ์ฒซ์งธ๋ ์ง์ ์์ด ๋ถํธ๋ถํ ๋ค์ค์ ์(DS-CDMA, direct-sequence code-division multiple-access) ์์คํ
์ ์ฌ์ฉ๋๋ ๋ฎ์ ์๊ด(correlation)์ ๊ฐ๋ ์ง PSK (phase-shift keying) ์ฑ์ข์์ ๋ค์ ์์ด์ด๋ฉฐ ๋์งธ๋ ์ฃผํ์๋์ฝ ๋ถํธ๋ถํ ๋ค์ค์ ์(FH-CDMA, frequency-hopping code-division multiple-access) ์์คํ
์ ์ฌ์ฉ๋ ์ ์๋ ๋ฎ์ ํด๋ฐ ์๊ด(Hamming correlation)์ ๊ฐ๋ ๋น์ด์ง ์์ด์ด๋ค.์ง์ ์์ด ๋ถํธ๋ถํ ๋ค์ค์ ์ ์์คํ
์ ์ฌ์ฉ๋๋ ํ์ฐ ์์ด๊ตฐ์ ๋๊ธฐ ํ๋์ ์ํด ๋ฎ์ ์๊ธฐ์๊ด(autocorrelation)์ ๊ฐ์ ธ์ผ ํ๋ฉฐ MAI (multiple-access interference)์ ์ํฅ์ ์ต์๋ก ํ๊ธฐ ์ํด ๋ฎ์ ์ํธ์๊ด(crosscorrelation)์ ๊ฐ์์ผ ํ๋ค. ๊ทธ๋ฌ๋ ๊ธฐ์กด์ ์ ์๋ ค์ง ํ์ฐ ์์ด๋ค์ ๋๋ถ๋ถ BPSK ํน์ QPSK ๋ณ์กฐ ์์ ์์ด๋ค์ด๋ฉฐ ์์ด ๊ธธ์ด์ ๋นํด ์์ ์์์ ์ ์ ์ ๋ํ์ฌ -PSK ๋ณ์กฐ์ ์ฌ์ฉ๋ ์ ์๋ ์ง ์์ด์ ๊ดํ ์ฐ๊ตฌ ๊ฒฐ๊ณผ๋ ๋งค์ฐ ๋ถ์กฑํ ์ค์ ์ด๋ค. ๋ณธ ํ์๋
ผ๋ฌธ์์๋ -PSK๋ฅผ ์ฌ์ฉํ๋ ํต์ ์์คํ
์ ์ฌ์ฉ๋ ์ ์๋ ์ง ์์ด์ ๊ดํ ์๋์ ์ฐ๊ตฌ ๋ด์ฉ๋ค์ ์๊ฐํ๋ค.์์ ์ ์์ ์ ์ ์ ๋ํด ์ฃผ๊ธฐ๊ฐ ์ธ ์ง ๋ฉฑ์์ฌ๋ฅ ์์ด(power residue sequence)์ ์์๊ณฑ(constant multiple) ์์ด๊ฐ ์ํธ์๊ด์ ๋ก ์๊ณ๋๋ฉฐ ์ฃผ๊ธฐ๊ฐ ์ธ ์ง Sidel'nikov ์์ด์ ์์๊ณฑ ์์ด๊ฐ ์ํธ์๊ด์ ์ผ๋ก ์๊ณ๋๋ค๋ ์ฌ์ค์ด ์๋ ค์ ธ์๋ค. ๋ณธ ํ์๋
ผ๋ฌธ์์๋ ๋จผ์ ์ด๋ฌํ ์์ด๋ค์ ์ํธ์๊ด ํจ์๊ฐ ์์ฝ๋น ํฉ(Jacobi sum)๊ณผ ์๋ถ์(cyclotomic number)์ ๊ด๋ จ๋์ด ์์์ ๋ณด์ด๊ณ ์ ์์ด๋ค์ ๊ฐ ์ํธ์๊ด ๋ถํฌ๋ค์ ์ ๋ํ๋ค.์ด ์ ์ฝ์์ผ ๋, shift-and-add ๋ฐฉ๋ฒ์ ์ด์ฉํ์ฌ ์ง ๋ฉฑ์์ฌ๋ฅ ์์ด์ ์์๊ณฑ ์์ด๋ค๋ก๋ถํฐ ๋ค ๊ฐ์ง ์์ด๊ตฐ์ ์ค๊ณํ๋ฉฐ ๊ฐ๊ฐ ์ต๋ ์๊ด์ด , ๋ก ์๊ณ๋จ์ ๋ณด์ธ๋ค. ๋ํ ์ค๊ณ๋ ๊ฐ ์์ด์ ์ ํ๋ณต์ก๋(linear complexity)๊ฐ ํน์ ๋ก ๋ํ๋จ์ ๋ณด์ธ๋ค. ๋์ผํ ๋ฐฉ๋ฒ์ ์ง Sidel'nikov ์์ด์๋ ์ ์ฉํ์ฌ ์ง ์์ด๊ตฐ์ ์ค๊ณํ ์ ์๋๋ฐ, ์๋ก ์ ์๋๋ ์์ด๊ตฐ ๋ ์ง๊ธ๊น์ง ์๋ ค์ง ์ง Sidel'nikov ์์ด๊ตฐ๋ค ๋ณด๋ค ๋ง์ ์์ด๋ค์ ํฌํจํ๋ฉด์ ์ต๋ ์๊ด์ ๊ดํ์ฌ ๋์ผํ ๊ฐ์ผ๋ก ์๊ณ๋๋ค.๋ง์ง๋ง์ผ๋ก ์๋ก ๋ค๋ฅธ ํ์์ธ ์์ , ์ ๋ํ์ฌ ์ด ๊ณผ ์ ๊ณต์ฝ์์ผ ๋, ์ฃผ๊ธฐ๊ฐ ์ธ ์ง generalized related-prime ์์ด์ ์๊ฐํ๋ค. ์ด ์์ด์ ์๊ธฐ์๊ด์ด ๊ณผ ์ค ํฐ ๊ฐ์ ์ํด ์๊ณ๋๋ฉฐ ์ ์๋ ์์ด๊ตฐ ๋ด์ ์๋ก ๋ค๋ฅธ ์์ด๊ฐ ์ํธ์๊ด์ ๋ก ์๊ณ๋๋ค.ํํธ ์ฃผํ์๋์ฝ ๋ถํธ๋ถํ ๋ค์ค์ ์ ๊ธฐ์ ์ ํ๊ฐ๋์ง ์์ ์คํํธ๋ผ์ ์ฌ์ฉํ ์ ์๋ ์ ๋น์ฟผํฐ์ค ๊ทผ๊ฑฐ๋ฆฌ ๋ฌด์ ํต์ ๋คํธ์ํฌ๋ฅผ ์ํ ๊ธฐ์ ๋ก์ ์ต๊ทผ ๊ฐ๊ด์ ๋ฐ๊ณ ์๋ค. WPAN (wireless personal area network)์ ๊ดํ IEEE 802.15 WG์ ํ์ค ๊ธฐ์ ์ธ ๋ธ๋ฃจํฌ์ค(Bluetooth)๊ฐ ๊ทธ ๋ํ์ ์ธ ์์ด๋ฉฐ, ์ฃผํ์๋์ฝ ๊ธฐ์ ์ ๋ ์ด๋ ๊ธฐ์ ์ด๋ ๋นํ๋ฅผ ๋ชฉ์ ์ผ๋ก ํ๋ ๊ตฐ์ฉ ํต์ ๋ฑ ๋ง์ ๋ถ์ผ์ ์์ฉ๋ ์ ์๋ค. ์ด๋ฌํ ์ฃผํ์๋์ฝ ๋์ญํ์ฐ ํต์ ์ ํต์ฌ ๊ธฐ์ ์ ๋ฐ๋ก ์ต์ ์ ์ฃผํ์๋์ฝ ์์ด ์ค๊ณ ๊ธฐ์ ์ ์๋ค.๋์งธ๋ก ๋ณธ ํ์๋
ผ๋ฌธ์์๋ ๋ฎ์ ํด๋ฐ ์๊ด์ ๊ฐ๋ ๋น์ด์ง ์ฃผํ์๋์ฝ ์์ด ์ค๊ณ์ ๊ดํ ์๋์ ๋ด์ฉ๋ค์ ์๊ฐํ๋ค.-FHS๋ ์ต๋ ํด๋ฐ ์๊ด์ด ์ด๊ณ ํฌ๊ธฐ๊ฐ ์ธ ์ฃผํ์ ์งํฉ์์ ๊ธธ์ด๊ฐ ์ธ ์ฃผํ์๋์ฝ ์์ด์ ๋ํ๋ธ๋ค. ์ต๊ทผ Ding๊ณผ Yin์ ๋ฅผ ๋ง์กฑํ๋ ์์๋ฉฑ(prime power) ์ ๋ํด Lempel-Greenberger ๊ฒฝ๊ณ์ ๋ํด ์ต์ ์ธ -FHS์ -FHS๋ค์ ๊ฐ๊ฐ ํฌํจํ๋ ๋ ์ฃผํ์๋์ฝ ์์ด ์งํฉ์ ์ค๊ณํ์๋ค. ๋ณธ ํ์๋
ผ๋ฌธ์์๋ ์ฃผํ์๋์ฝ ์์ด ์งํฉ์ ๊ดํ Ding๊ณผ Yin์ ์ ๋ฆฌ์ ๊ดํ ๋ฐ๋ก๋ฅผ ์ ์ํ๊ณ ์ด๋ฅผ ์์ ํ๋ค. ๋ํ ์ด๋ฌํ ์ฃผํ์ ๋์ฝ ์์ด๋ค์ด Sidel'nikov ์์ด๊ณผ ๋ฐ์ ํ ๊ด๋ จ๋์ด ์์์ ๋ณด์ด๊ณ ๊ธฐ์กด์ Sidel'nikov์ ์ํด ์ ๋๋ nearly equidistant code์ ํด๋ฐ๊ฑฐ๋ฆฌ(Hamming distance)์ ๋ํ ์ ๋ฆฌ๋ฅผ ์์ ํจ์ผ๋ก์จ ์ฃผํ์๋์ฝ ์์ด์ ๊ดํ ์๋ก์ด ํ๋ผ๋ฏธํฐ๋ฅผ ์ ์ํ๋ค. ๋์ผ๋ก ์๋ก ๋ค๋ฅธ ํ์์ธ ์์ , ์ ๋ํ์ฌ ์ด ๊ณผ ์ ์ง์์ธ ๊ณต์ฝ์์ผ ๋, Lempel-Greenberger ๊ฒฝ๊ณ์ ๋ํด ์ค์ต์ ์ธ(near-optimal)์ธ -FHS๋ฅผ ์ค๊ณํ๋ค.Pseudorandom sequences have widespread applications in the area of communication and digital signal processing systems including spread spectrum, stream ciphers, radar ranging, channel estimation, packet transmission synchronization, and etc. In particular, spreading sequences for multiple access are essential parts in spread spectrum communication systems.The objective of this thesis is to study sequences with low correlation over a nonbinary alphabet with respect to two different correlation measures. First, we focus on polyphase sequences with low periodic correlation over -ary phase-shift keying (PSK) constellation for direct-sequence code-division multiple-access (DS-CDMA) systems. Second, we study nonbinary sequences with low periodic Hamming correlation over an arbitrary alphabet for frequency-hopping code-division multiple-access (FH-CDMA) systems. Several optimal sequence families have been known for quadriphase and prime-phase cases. However, construction methods for optimal sequence sets with arbitrary alphabet size are less known. Recently, it was shown that the magnitude of the crosscorrelation between any distinct constant multiple sequences of an -ary power residue sequence of period is upper bounded by and that of an -ary Sidel'nikov sequence of period is upper bounded by , where is a prime and is a positive integer.In this thesis, firstly, we show that their crosscorrelation functions are closely related to Jacobi sums and cyclotomic numbers. We then derive the crosscorrelation distribution of constant multiple sequences of an -ary power residue sequence. In the case of constant multiple sequences of an -ary Sidel'nikov sequence, we get the possible crosscorrelation values whose occurrence numbers are expressed in terms of the cyclotomic numbers of order and are possibly zero.Secondly, we construct four -ary sequence families from a power residue sequence of odd prime period and its constant multiple sequences using the shift-and-add method, when is a divisor of . We show that the maximum correlation values of the proposed sequence families are upper bounded by or . In addition, we prove that the linear complexity of each sequence in the proposed families is either or . We also construct an -ary sequence family from {\em Sidel'nikov sequences} of period by applying the same method, when is a divisor of . The proposed sequence family has larger size than the known -ary Sidel'nikov sequence families, whereas they all have the same upper bound on the maximum correlation.We also introduce new -ary sequences of length , called generalized -ary related-prime sequences, where and are distinct odd primes, and is a common divisor of and . We show that their out-of-phase autocorrelation values are upper bounded by the maximum between and . We also construct a family of generalized -ary related-prime sequences and show that the maximum correlation of the proposed sequence family is upper bounded by . Thirdly, we study on the construction of frequency-hopping sequences (FHSs). FH-CDMA systems have been widely used to short-range wireless networks utilizing the unlicensed spectrum, called wireless personal area network (WPAN) or military communication applications needed to be robust to jamming environment. For these systems, FHSs are required to have low Hamming correlation for minimization of interference of frequencies.A -FHS denotes a frequency-hopping sequence of length over a frequency set of size with maximum out-of-phase Hamming autocorrelation . Recently, Ding and Yin constructed two FHS families for a prime power satisfying with positive integers and . Theorems 4 and 5 in their paper claim that these two FHS families include optimal -FHSs and -FHSs with respect to the Lempel-Greenberger bound, respectively. In this thesis we give counterexamples and make corrections to them. Furthermore, we observe that these FHSs are closely related to Sidel'nikov sequences. Based on our results on the spectrum of their Hamming autocorrelation values, we also correct the theorem on the spectrum of Hamming distances of nearly equidistant codes derived by Sidel'nikov and show that -FHSs for odd and are new FHSs with the parameters not covered in the literature.In the last part of this thesis, we construct near-optimal -FHSs whose maximum Hamming autocorrelation is given by where is the optimal Hamming autocorrelation value with respect to the Lempel-Greenberger bound, where and are distinct odd primes, and is an even common divisor of and