Error detection/correction and fault detection/recovery – Pulse or data error handling – Error count or rate
Reexamination Certificate
1999-05-18
2001-11-06
Baker, Stephen M. (Department: 2133)
Error detection/correction and fault detection/recovery
Pulse or data error handling
Error count or rate
C370S468000, C714S776000
Reexamination Certificate
active
06314535
ABSTRACT:
FIELD OF THE INVENTION
The present inventions pertain to the field of error correction in communication systems, including more specifically, forward error correction arrangements.
BACKGROUND OF THE INVENTION
Digital communications systems utilize communication channels over which traffic data is communicated. These channels are typically bandwidth limited, having a finite channel capacity. The channel capacity together with other properties of the channel, such as various forms of noise and interference, will, with statistical certainty, cause, or otherwise result, in the injection of error conditions in the traffic data communicated over the channel. The effects of these error conditions may be particularly evident in wireless communications systems, which utilize generally unpredictable over-the-air communications channels through which remote stations communicate with a central station.
A technique for eliminating, or at least reducing, the effects of these error conditions is called Forward Error Correction (FEC). In general, the employment of an FEC technique entails transmitting error detection data and error correction data along with the bearer data. The error detection data and error correction data are typically derived from the bearer data itself by employing an error detection algorithm and error correction algorithm known to the receiver as well as the transmitter, and in the case of a digital wireless communications systems, a remote station and a central station in communication with one another.
FEC techniques have been employed in Time Division Multiple Access (TDMA) and Code Division Multiple Access (CDMA) wireless communications systems. For example, TDMA systems typically allow communication between a plurality of remote stations and a central station using the same frequency band and transmitting bearer data between remote stations and the central station during discrete time periods (i.e., each remote station transmits and receives bearer data broken up into bearer data bursts during respective time slots of cyclically repeating time frames).
In wireless communication, prior to transmission, the central station or remote station appends or encodes the bearer data with error detection data and error correction data according to a respective error detection algorithm and error correction algorithm. The reciprocal remote station or central station receives each error correctable bearer data packet, automatically corrects any errors in each error correctable bearer data packet (within the limits of the error correction algorithm) by processing the error correctable bearer data packet according to the error correction algorithm, and detects any residual errors in each corrected bearer data packet by processing the corrected bearer data packet according to the error detection algorithm.
The use of an FEC technique to eliminate or reduce the effects of transmission errors, however, does not come without a cost to the communications system. The transmission bandwidth available to a user transmitting in a particular time slot in known systems is reduced by the overhead required to transmit the error correction data. The transmission of error correction data with each error correctable bearer data packet can require 100% or more overhead in some instances. This increase in overhead typically results in either a longer time slot or a reduction in the bandwidth available for the traffic data (for a fixed transmission bit rate). In addition, in known wireless communications systems, the Bit Error Rate (BER) of the traffic data communicated between a central station and a remote station depends on dynamically varying conditions, such as, the relative distance between the remote station and the central station, interference, environmental conditions, traffic data transmission rate, etc.
As a result, the BER of bearer data transmitted between the central station and a remote station varies with each particular remote station and with time with respect to each remote station making it difficult to systematically select an FEC error correction algorithm that optimizes both the transmission overhead and error protection capability. To provide high quality communication between the central station and any given remote station during any given time period, the error correction algorithm is generally selected based on the worst-case BER, and is thus overly robust in most situations, resulting in undesirably high overhead and reduced overall data throughput for the system.
There thus is a need for a communications system that employs an FEC arrangement that among other things, maximizes the amount of bearer data transmitted between the central station and any given remote station at any given time, while still providing an acceptable error rate.
SUMMARY OF THE INVENTION
The present inventions comprise a novel method of dynamically varying the transmission of error correction data in communications systems.
In a preferred method of the present inventions, a first plurality of error correctable bearer data packets is transmitted between a first communications device and a second communications device during a first multi-frame (i.e., a plurality of time frames). An initial error correction algorithm is selected from a plurality of error correction algorithms, which is then employed to generate error correction data. The error correction data is transmitted with the bearer data packets by, such as, e.g., appending or encoding the error correction data thereto, creating the first plurality of error correctable bearer data packets. The plurality of error correction algorithms can comprise any number of different error correction algorithms, which may include no error correction algorithm. Upon receipt of the first plurality of error correctable bearer data packets, errors that are injected into the first plurality of error correctable bearer data packets during the transmission thereof are corrected within the limits of the selected error correction algorithm.
The error rate level of the communications channel between the first communications terminal and the second communications terminal is determined during the first multi-frame. The error rate level of the communications channel may be determined by such techniques as, e.g., measuring the number of defective corrected bearer data packets (i.e., block error rate (BLER)) or measuring the number of bit errors in the uncorrected bearer data packets (i.e., bit error rate (BER)). A subsequent error correction algorithm, which may be the same as the initial error correction algorithm, is selected from the plurality of error correction algorithms based in part upon the determined error rate level.
A second plurality of error correctable bearer data packets is transmitted between the first communications terminal and the second communications terminal during a second multi-frame. The subsequent selected error correction algorithm is employed to generate error correction data, which is transmitted with the second plurality of error correctable bearer data packets. The second plurality of error correctable bearer data packets are corrected within the limits of the second selected error correction algorithm. The error rate level of the communication channel between the first communications terminal and the second communications terminal is determined during the second multi-frame. A third error correction algorithm, which can be the same as or different from the second selected error correction algorithm, is selected from the plurality of error correction algorithms based in part upon the determined error rate level.
The third selected error correction algorithm is employed to correct the third plurality of error correctable bearer data packets transmitted between the first communications terminal and the second communications terminal during the third multi-frame. This error correction algorithm selection and error correctable bearer data packet correction process is repeated during future multi-frames.
REFERENCES:
patent: 4908827 (199
Barabash Darrell W.
Morris Russell A.
Baker Stephen M.
Lyon & Lyon LLP
Xircom Wireless, Inc.
LandOfFree
Dynamic forward error correction does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dynamic forward error correction, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dynamic forward error correction will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2593903