Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1998-09-09
2002-06-04
Chin, Wellington (Department: 2664)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S310000, C714S746000, C714S774000, C455S426100
Reexamination Certificate
active
06400728
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to digital information systems. More particularly, the present invention relates to digital enhanced cordless telephony (DECT), and other error-prone digital data transmission systems.
BACKGROUND ART
The transmission of digital information and data between systems has become an essential part of commonly used systems. With such systems, information content is transmitted and received in digital form as opposed to analog form. Information long associated with analog transmission techniques, for example, television, telephone, music, and other forms of audio and video, are now being transmitted and received in digital form. The digital form of the information allows signal processing techniques not practical with analog signals. In most applications, the user has no perception of the digital nature of the information being received.
Many digital communication devices (particularly wireless digital telephones) suffer some amount of signal degradation during the transmission from the originating device to the receiving device. This degradation often results in the loss of some information, some distortion in the signal, or some noticeable noise in the received signal (e.g., as in the case of a wireless telephone). Generally, the more frequent the errors, the more significant the loss of information at the receiving device, which consequently leads to more objectionable performance of the communications system.
To correct this problem, the electronics industry has adopted various error correction techniques which counteract the effects of signal degradation and improve or ensure the integrity of the information at the receiving device. Hence, many digital communications systems available on the market use error correction methods that are each able to accomplish reasonable communication quality under normal operating conditions.
Typically, error correction techniques function by including additional amounts of “redundant” information in the signal transmission from the originating device. This redundant information is often referred to as error correction code. The redundant information is used to check the validity of the information as received at the receiving device. For example, parity checking, check summing, cyclic redundancy checking, forward error correction coding, are several of the more widely used, well known error correction methods. These error correction methods help ensure the integrity of the received information, thereby ensuring the proper and error free operation of any applications being run on top of the received information, such as, for example, a wireless modem link supporting a remote network node. The problem with the above error correction methods is that they add varying amounts of latency to the data transmission. This latency is due to the processing required in implementing the chosen error correction scheme. Another problem is the fact that the additional error correction code increases the spectrum bandwidth required by a transmission channel (e.g., an RF channel between the transmitting and receiving devices) to transmit the desired information. And yet another problem is the fact that the error correction code requires increased signal processing in both the transmitter and the receiver, thereby increasing power consumption and, in the case of small, portable devices, decreasing battery life.
With most digital transmission systems, there exist several different error correction processes which can be implemented. The error correction processes differ in strength and processor intensiveness. Strength refers to the ability of the error correction process to continue transmitting and receiving data with acceptable error rates in the presence of noise and interference (e.g., noise from the transmitter/receiver hardware, noise from the external environment, noise in the communications channel, etc.). Processor intensiveness refers to the number of processor cycles consumed executing the error correction process (e.g., processor time spent encoding the data on the transmitter side and decoding the data on the receiver side). The stronger error correction processes involve the transmission of increased amounts of redundant error correction code and the use of more sophisticated encoding schemes, and thus, are more processor intensive. When transmission conditions are bad (e.g., large number of errors in the communications channel) the stronger, more processor intensive, error correction processes yield more favorable error rates than weaker, less processor intensive error correction processes.
The more fault intolerant the application with which the digital communication system is used, the stronger, and hence, more processor intensive, the error correction process is required to be. Thus, for example, in applications such as distributed computer networks applications which require the accurate transmission of large amounts of data to the various distributed computer nodes, extremely strong error correction processes are used. The strong error correction is highly processor intensive, and hence, adds a significant amount of latency, spectrum bandwidth and power to the communication system. In other applications, such as, for example, voice based telephony, the presence of errors in the data (e.g., digitized voice) does not significantly impair performance of the application. Most people can understand voice communication with small to moderate amounts of noise (e.g., data errors). However, most people are very much annoyed by latency in the communications system. Thus, in voice applications, faster error correction processes are required.
Accordingly, the power and the amount of error correction used is typically chosen such that the communications system or the application being served by the communications system will run satisfactorily under average operating conditions. If a greater degree of reliability is required, stronger, high latency error correction routines are used. If low latency is required, fast executing error correction is used.
The problem, however, is the fact that in most cases these error correction methods are static. They are typically chosen during the design process of the communications system. A static error correction method is chosen and designed into a communications system in accordance with the typical expected operating conditions of the system. Static error correction is, in this manner, a design compromise based upon the expected use of the system. For example, in a communication system which can be used for both voice and data applications (e.g., voice based telephony and fax transmission, file transfer and internet access).
The type of user data transferred using the communications system is typically unknown, or alternatively, selected by the user. In the case where the type of data typically transferred is not determined (i.e., unknown), assumptions about the data type are built into the device at the time of its manufacture, which accordingly tend to dictate the primary use of the device.
In the case of user selection, the user specifies which error correction process to use by specifying the type of data (e.g., voice or fax or file transfer or internet access) is to be transferred. The disadvantage with the user selected data type scheme is that the user may neglect to enter such information to the communication system or may make mistakes when doing so. If the incorrect data type is selected, the communications system operates using wrong or sub-optimal error correction methods for data transmission and error handling.
Because of these difficulties, the choice of error correction processes that can be used are often reduced so that even a signal having the tightest restrictions on a certain feature can successfully be transmitted and received even when wrong type information has been entered. In essence, the communications system uses error correction processes which are able to guarantee successful transmission even where the data type is incorrectly as
Chin Wellington
Tran Maikhanh
VLSI Technology Inc.
Wagner , Murabito & Hao LLP
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