Demodulators – Frequency modulation demodulator – Having specific distortion – noise or other interference...
Reexamination Certificate
2002-03-05
2004-11-23
Lam, Tuan T. (Department: 2816)
Demodulators
Frequency modulation demodulator
Having specific distortion, noise or other interference...
C329S320000, C329S321000
Reexamination Certificate
active
06822508
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a communication device, a communication method, a program, and a storage medium. More particularly, the present invention relates to a communication device, a communication method, a program, and a storage medium storing a program, which allow multiple access in UWB (ultra wideband) communication.
2. Description of the Related Art
UWB communication is also called impulse radio communication and is expected to find various applications, as discussed for example, in “Impulse radio: How it works” by M. Z. Win and R. A. Scholtz (IEEE Communication Letters, Vol. 2, pp. 36-38, February, 1998 (hereinafter, this literature will be denoted as “Ref. 1”)), “UWB waveforms ad coding for communications and radar” by L Fullerton (Proc. IEEE Telesystems Conf., pp. 139-141, Mar. 26-27, 1991 (hereinafter, this literature will be denoted as “Ref. 2”)), and “Answers to questions posed by Bob Lucky, Chairman of the FCC's Technical Advisory Committee (e-mail correspondence, http://ultra.usc.edu./ulab, Jun. 29, 1999 (hereinafter, this literature will be denoted as “Ref. 3”)).
In UWB communication, data is transmitted using a very short pulse at low power without using a carrier. To transmit such a very short pulse, a wide bandwidth on the order of several GHz is used, as described, for example, in Ref. 1 or 2.
The UWB communication technology has many advantages that stem from its ultra-wideband nature, as described in, for example, “On the robustness of ultra-wideband width signals in dense multipath environments” by M. Z. Win and R. A. Scholtz (IEEE Communication Letters, Vol. 2, pp. 51-53, February, 1998 (hereinafter, this literature will be denoted as “Ref. 4”)), and “On the analysis of UWB communication channels” by J. M. Cramer, R. A. Scholtz, and M. Z. Win (Proc. IEEE Military Communications Conf., pp. 1191-1195, Oct. 31 to Nov. 3, 1999 (hereinafter, denoted as “Ref. 5”)). More specifically, it can penetrate walls, experience significantly less fading, offer extremely fine time-resolution, and deliver large processing gains.
In particular, the absence of a carrier signal in the UWB communication obviates the need for radio frequency (RF) or intermediate frequency (IF) circuits. This allows reductions in device size and power consumption.
These characteristics of the UWB communication technology give it substantial advantages over conventional narrowband, wideband and infrared wireless communication systems.
Potential applications of the UWB communication include wireless local area networks (LAN), information distribution systems for use in a medical application or the like, outdoor or indoor wireless multiple-access communication systems, ranging devices, and other many applications, as described in, for example, “Catching the wave; Breakthroughs in wireless technology” by J. S. Gage (MD Computing: The Leading Edge in Medical and Healthcare Informatics, Vol. 16, March/April 1999 (hereinafter, denoted as “Ref. 6”)), and “Ultra-wideband width time-hopping spread-spectrum impulse radio for wireless multiple-access communications” by M. Z. Win and R. A. Scholtz (IEEE Trans. Communications, Vol. 48, pp. 679-691, April, 2000 (hereinafter, denoted as “Ref. 7”)).
There is a great need for applying the UWB communication technology to multiple-access (multi-user) communication with a plurality of communication terminals. The idea of applying UWB to multiple-access communication is discussed in, for example, “Multiple access with time-hopping impulse modulation” by R. A. Scholtz (Proc. IEEE Military Communications Conf. (Boston, U.S.), pp. 447-450, Oct. 11-14, 1993 (hereinafter, denoted as “Ref. 8”)), and “Multiple-access performance limits with time hopping and pulse position modulation” by F. Ramirez-Mireles and R. A. Scholtz (Proc. IEEE Military Communications Conf., pp. 529-533, Oct. 18-21, 1998 (hereinafter, denoted as “Ref. 9”)).
UWB multiple-access communication systems proposed in Refs. 7 to 9 are conceptually similar to asynchronous code-division multiple-access (CDMA) systems in certain aspects. Transmitted signals of each user (signals transmitted from each communication terminal) share a common spectrum, and the set of signaling waveforms across all users are not necessarily orthogonal.
The multiple-access capability of a UWB system is primarily determined by the processing gain that is given by the pulse bandwidth to the pulse (or symbol) repetition frequency (RPF) ratio. In the UWB communication, its very wide frequency bandwidth results in a high processing gain. The UWB communication technology is very different from the CDMA communication technology in that the high processing gain of the UWB communication allows it to be advantageously employed in applications in which power is limited.
In the literatures Ref. 1 and Refs. 7 to 9, it is proposed to realize multiple-access UWB communication by time-hopping the timing of transmitting pulse-position-modulated signals of respective users on the basis of a time-hopping sequence indicated by a pseudorandom number.
Herein, the “pulse position modulation” refers to modulation of pulse positions depending on data to be transmitted. For example, a unit period with a predetermined length is assigned to one symbol, and each period is divided into M intervals. A pulse is placed in one of the M intervals, at a position corresponding to data to be transmitted. The “time hopping” refers to an operation of, rather than transmitting symbols (unit periods) at fixed intervals, randomly shifting the transmission timing from the fixed intervals.
In the proposed UWB multiple-access communication techniques, each receiving device includes a single-user demodulator for detecting the pulse position, in each unit period, of a pulse-position-modulated signal.
The single-user demodulator includes a filter bank including filters for matching the received signal with pulses at possible positions in unit periods, and a detector for detecting a filter that provides a highest output among the filters of the filter bank, and employing, as demodulated data, a value corresponding to a pulse position that is matched with the received signal by the filter that is determined to provide the highest output.
Ideally, in the multiple-access communication, there is no overlap among pulses of signals transmitted from users. Under such an ideal condition, the single-user demodulator can function as an ideal demodulator for demodulating a pulse-position-modulated signal in an environment including additive white Gaussian noise. In this case, the single-user demodulator may be constructed in a similar fashion to a single-user matched filter for detection in CDMA systems, as described, for example, in “Multiuser detection for CDMA systems” by A. Duel-Hallen, J. Holtzman and Z. Zvonar (IEEE Personal Communications Magazine, Vol. 2, pp. 46-58, April, 1995 (hereinafter, denoted as “Ref. 10”)), “Multi-user detection for DS-CDMA communications”, by S. Moshavi (IEEE Communications Magazine, Vol. 34, pp. 124-136, October, 1996 (hereinafter, denoted as “Ref. 11”)), and “Multiuser Detection” by S. Verdu (Cambridge University Press, 1998 (hereinafter, denoted as “Ref. 12”)).
However, in practical multiple-access communication systems, interference occurs among signals transmitted from users (hereinafter, such interference will be referred to as multiple-access interference), and multiple-access interference (MAI) is generally not Gaussian. The conventional single-user modulator is no longer optimal in such an environment in which MAI can occur.
MAI increases with the number of multiple-access users, and the increase in MAI causes various adverse effects on the single-user demodulator. When data is transmitted at a high rate, the resultant high pulse repetition frequency causes a reduction in the processing gain and thus an increase in MAI.
In view of the above, it is an object of the present invention to provide a high-performance demodulator for use in UWB multiple-access communication.
SUMMARY OF THE
Kohno Ryuji
Yoon Young C.
Lam Tuan T.
Maioli Jay H.
Nguyen Hiep
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