Data processing: speech signal processing – linguistics – language – Audio signal bandwidth compression or expansion
Reexamination Certificate
1999-08-31
2004-08-10
Dorvil, Richemond (Department: 2655)
Data processing: speech signal processing, linguistics, language
Audio signal bandwidth compression or expansion
C704S501000, C704S503000, C704S226000, C704S228000
Reexamination Certificate
active
06775654
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an apparatus for extracting digital audio information from data which contains digital audio information and is transmitted by way of a radio transmission path, and for decoding the extracted digital audio information and reproducing an audio signal. More particularly, the present invention relates to a digital audio reproducing apparatus suitable for use in a mobile receiver for receiving digital broadcasting programing broadcast by a satellite.
(2) Description of Related Art
Recently, in parallel with putting digital satellite broadcasting into practice, there have been developed and proposed various image data compression system, audio data compression systems and the like. Also, there are discussed systems of various manner for receiving digital satellite broadcasting by a receiver carried in a mobile unit.
When satellite broadcasting is to be received, in general, it is necessary to prepare a parabolic antenna for receiving the radio wave of which frequency is allocated by an authority. Therefore, it was unrealistic for a user of the mobile unit to prepare such an antenna to receive the satellite broadcasting. However, since S-band (2.6 GHz band) frequency (which is particularly unsusceptible against rain), is allocated for mobile units to receive the satellite broadcasting, it is realistic for the mobile user who lacked receiving means to now receive sought-after satellite broadcasting.
When data containing digital audio information is transmitted from a geostationary satellite to a portable receiving terminal or a terminal carried in a vehicle on the ground in a broadcasting situation with mobile units as targets, the data containing digital audio information is sometimes dropped midway of the radio wave transmission. This occurs when the mobile unit passes through the shadow place of the broadcast radio wave such as a crowded group of buildings, trees, a bridges under a tunnel and so on, such that the broadcasting radio wave is prevented from being transmitted by these obstacles, resulting in a broadcast break on the receiving side. In the field of broadcasting technology, it is substantially impossible to send data repeatedly from the broadcasting station to each of the plural receivers upon each repeating broadcasting request. Therefore, it is essential to keep a reproduction of the broadcasting data even at breaks in the radio wave reception.
In a receiving environment in which the mobile unit receives radio waves as described in the above manner, when a mobile unit on the ground fails to receive transmitted data from the geostationary satellite in a normal fashion, a disturbance is caused in a picture or a break in audibility. Although it is relatively easy to reduce the annoyance of a video program viewer from the disturbance in picture reproduction, it is quite difficult to reduce the annoyance coming from breaks in the sound with the mere countermeasure of muting or the like. Particularly, when audio broadcasting is provided for mobile unit users and the driver of a vehicle is listening to a broadcast of sound intensively, any sound breaks are truly annoying. Thus, there is a great need to improve audibility in such conditions.
The following novel measures have been taken to resolve the above-mentioned challenges.
{circle around (1)} When the radio wave transmission is interrupted due to any obstacle, novelty the receiving terminal stops broadcast reproduction.
{circle around (2)} If the “shadow area” of the broadcasting satellite is caused in a wide area, a gap filler (retransmission equipment) or similar equipment is installed to reduce the radio wave shadow area. Alternatively, a plural number of broadcasting satellites remote from one another are utilized for transmitting radio waves to novelly resolve the above challenges.
{circle around (3)} Error correction functions, for example, one using an interleave, intraframe coding, interframe coding and so on are driven to restore lost data, and depth of the interleave and code length of the error correction code are optimized to cope with the obstacle of the radio wave transmission gap.
{circle around (4)} Radio wave transmission is carried out by using a time diversity system in which the same transmission data is transmitted with a time lag.
However, a break in transmission interrupts as described in item {circle around (1)} above. Because of this break in transmission the annoyance to a listener is unacceptable. Particularly when an audio broadcast is provided for mobile unit users, such interruption in the radio wave reception draws attention to the user with a broken signal so there is a definite need to avoid such interruptions. The avoidance of such interruptions may be solved as disclosed herein by the invention.
The countermeasure gap filler introduced in item {circle around (2)} is effective because radio waves are supplied from the gap fillers to the “shadow area” of the satellite radio wave which can extend beyond the “shadow area” gap in transmission caused by buildings. However, there are numerous “shadow areas” across the country such as the “shadow areas” of groups of small buildings, trees, a large-sized vehicle approaching from an opposite side of a road and the like. Therefore, it is unrealistic from an economic standpoint to install gap fillers to eliminate all possible “shadow areas.” Numerous areas are left in which it is incapable of receiving a radio wave. Further, even if a reasonable number of gap fillers are installed, the economic constraints will result in the “shadow areas” being made too small, the radio wave receiver eventually moving to another area in which it becomes capable of receiving the radio wave again. However, if the receiver is carried in a mobile unit such as a motor vehicle, when the vehicle passes through an area in which the radio wave is not supplied it is inevitable to have a point in which the radio waves are not received. Furthermore, if another mobile unit is as an obstacle preventing radio waves from being transmitted, the temporary lack of reception of the radio wave is brought about.
On the other hand, if a plurality of broadcasting satellites are available for transmitting radio waves, it is possible to reduce the areas in which the radio waves are not received. However, it is difficult to achieve a reasonable effect due to the economic cost of providing satellite coverage. For example, if a relatively inexpensive geostationary satellite for use as a BS broadcasting is utilized to serve also as the audio signal broadcasting means, the greater the area in which the radio wave reception is attempted apart from the equator, the smaller angle of elevation directing the north or south orientation now becomes available for receiving radio waves. Further, if a LEO (Low Ear Orbit) satellite is employed for supplying radio waves, for example, more than totally eight satellites may be utilized; with at least four satellites on each of the two orbits intersecting with each other at right angle, at a great amount of installation cost.
If the scheme of interleave or error correction introduced in the item {circle around (3)} is employed, the bit error cannot be eliminated completely. For example, if a coded data compression system such as an MPEG system is employed, decoding is carried out at the unit of the frame. Therefore, there can exist a case in which a frame is deleted in spite of the fact that the frame contains only one bit error. Yet, much redundant data will be generated adding for error correction, resulting in the deterioration of radio wave utilization efficiency.
Further, if the time diversity system described in item {circle around (4)} is employed, another carrier wave will be prepared, leading to deterioration in the channel utilizing efficiency.
SUMMARY OF THE INVENTION
The present invention in view of the above aspects, with an object of the present invention, for example, to provide a digital audio reproducing apparatus of a simplicity which provides a solution
Katoh Tadayoshi
Matsushima Kazuhisa
Okubo Hiroshi
Saito Takashi
Yokoyama Hideaki
Dorvil Richemond
Katten Muchin Zavis & Rosenman
Nolan Daniel
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