Multiplex communications – Generalized orthogonal or special mathematical techniques – Fourier transform
Reexamination Certificate
1998-03-12
2001-04-17
Chin, Wellington (Department: 2664)
Multiplex communications
Generalized orthogonal or special mathematical techniques
Fourier transform
C370S291000, C375S232000, C375S285000, C375S350000, C455S065000, C455S506000
Reexamination Certificate
active
06219334
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a receiving apparatus for use with a radio communication system for transmitting for example an orthogonal frequency division multiplexing signal (hereinafter referred to as OFDM signal) and a receiving method thereof.
2. Description of the Related Art
In a recent radio communication system, a performance for transmitting a large amount of information such as picture data, in particular, moving picture data, as well as simple text data is required. Thus, in such a radio communication system, a highly efficient modulation system such as 16-ary QAM system or 64-ary QAM system should be essentially used. The 16-ary QAM system and 64-ary QAM system are modulation systems that modulate information with an amplitude or a phase that varies.
Consequently, such a receiving apparatus (hereinafter referred to as receiver) for use with a conventional radio communication system comprises an RF receiving means for receiving a radio signal modulated corresponding to the 16-ary QAM system or 64-ary QAM system and a demodulating means for coherent detection of the received signal and demodulating the received signal to an original data sequence.
However, in such a radio communication system, due to a multi-path propagation environment, the amplitude and phase of a signal waveform largely distort. Thus, when the receiver receives a distorted radio signal and coherently detects the received signal, a received data sequence that is different from the original data sequence is obtained.
To solve this problem, a technology that cancels or alleviates the distortions of amplitude and phase should be employed in the receiver.
For example, to alleviate the distortion of a channel, a technology for transmitting a reference signal from the transmitter and obtaining the channel distortion with the waveform of a reference signal received by the receiver is known.
When the channel distortion is obtained, the original transmitted signal can be estimated with the received signal. Thus, the receiver performance can be improved.
For example, in the environment of which the above-described orthogonal frequency division multiplexing (OFDM) signal is transmitted, the channel response (in the frequency domain) of the channel can be calculated with each received reference signal and each transmitted reference signal generated by the receiver. However, the channel frequency response contains a thermal noise and so forth generated in the receiver. To suppress the thermal noise, the calculated channel frequency response should be filtered in the frequency domain by a particular filtering means.
When the channel frequency response is filtered in the frequency domain, the Gaussian noise component can be suppressed. Thus, the channel frequency response calculated by the receiver can be approached to the channel frequency response with no Gaussian noise.
In this case, a filtering means with a bandwidth corresponding to the channel frequency response should be used.
In other words, when the bandwidth of the filtering means is designated to a value larger than a proper value, the channel frequency response that has been filtered still contains a large noise component. In contrast, when the bandwidth of the filtering means is designated to a value smaller than the proper value, the channel frequency response gets distorted. Thus, in both the cases, good receiver performance cannot be obtained.
However, in the receiver (receiving apparatus) for use with the conventional radio communication system, the channel frequency response largely depends on the propagation environment of a radio wave. When the moving receiver receives a radio signal, since the propagation environment of the radio wave largely varies, it is almost difficult to use a filtering means with a bandwidth suitable for the propagation environment of the radio wave that varies in such a manner.
SUMMARY OF THE INVENTION
The present invention is made from the above-described point of view.
A first object of the present invention is to improve receiver performance of a receiving apparatus.
A second object of the present invention is to properly compensate the distortion of a received signal due to a multi-path propagation environment even if the propagation environment of a radio wave varies.
To accomplish the above-described objects, the present invention is a receiving apparatus, comprising an RF receiving means for receiving an orthogonal frequency division multiplexing signal, a transforming means for transforming the orthogonal frequency division multiplexing signal received by the RF receiving means into a frequency spectrum signal, a reference signal generating means for generating a reference frequency spectrum signal, a channel frequency response calculating means for calculating a channel frequency response with the reference frequency spectrum signal generated by the reference signal generating means and the frequency spectrum signal transformed by the transforming means, a filtering means for filtering the channel frequency response calculated by the channel frequency response calculating means, a delayed signal estimating means for estimating a delayed signal due a multi-path propagation environment received by the RF receiving means, a bandwidth designating means for designating the bandwidth of the filtering means with information of the delayed signal estimated by the delayed signal estimating means, a distortion compensating means for compensating a distortion in the frequency domain due to the multi-path propagation environment of the frequency spectrum signal transformed by the transforming means with the channel frequency response filtered by the filtering means, and a demodulating means for demodulating the frequency spectrum signal whose distortion has been compensated by the distortion compensating means to a digital data sequence.
Conventionally, the channel frequency response in the frequency domain due to the multi-path propagation environment is calculated with a received signal and a reference signal. However, since the calculated channel frequency response contains a noise, the noise should be suppressed from the channel frequency response by the filter. At this point, it is important to designate the bandwidth of the filtering means that filters the channel frequency response.
Thus, the receiving apparatus estimates a delayed signal due to a multi-path propagation environment and designates the bandwidth of the filtering means corresponding to the estimated result. Consequently, the bandwidth of the filtering means corresponding to the propagation environment can be designated and thereby the noise can be optimally suppressed. Thus, since the distortion of the received signal can be properly compensated, the receiver performance can be improved.
Moreover, in the receiving apparatus, since a plurality of power or amplitude levels and delay times of a estimated delayed signal are stored and the bandwidth of the filtering means is designated corresponding to such information, the designating accuracy of the bandwidth of the filtering means can be improved. In addition, even if the propagation environment instantaneously changes, the designated bandwidth of the filtering means can be prevented from being changed.
Normally, the channel frequency response tends to be affected by a delayed signal with a high reception level.
Thus, since the receiving apparatus designates the bandwidth of the filtering means with the delay time of a delayed signal accurately, even if a plurality of delayed signals arrives at the receiver, the receiving apparatus can designate the bandwidth of the filtering means corresponding to the propagation environment at the point.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.
REFERENCES:
patent: 5483529 (1996-01-01), Baggen et al.
patent: 5802117 (1998-09-0
Namekata Minoru
Sato Kazumi
Chin Wellington
Duong Frank
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Receiving apparatus for receiving orthogonal frequency... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Receiving apparatus for receiving orthogonal frequency..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Receiving apparatus for receiving orthogonal frequency... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2451484