Pulse or digital communications – Equalizers – Automatic
Reexamination Certificate
1997-05-08
2001-10-23
Luther, William (Department: 2664)
Pulse or digital communications
Equalizers
Automatic
C370S292000
Reexamination Certificate
active
06307883
ABSTRACT:
FIELD OF THE INVENTION
The subject invention relates to wireless communication and, particularly, to tracking performance of a whitening operation and an adaptive operation on data in wireless communication.
BACKGROUND ART
Usually, in mobile wireless communication, a transmitter sends a signal as shown in FIG.
6
. That is, a wireless signal includes a training sequence
10
, a header
20
, and data
30
. Upon reception of a wireless signal of this type, a receiver establishes synchronization with the wireless signal by using a carrier frequency or some other parameters, and calculates and sets tap coefficients etc. (an adaptive operation by an adaptive algorithm) of its own equalization filter (also called “adaptive filter”) by using the training sequence
10
to eliminate influences of intersymbol interference. Once the tap coefficients of the equalization filter are set, influences of intersymbol interference can be eliminated; therefore, it becomes possible to receive data contained in the header
20
and the data
30
that follow the training sequence
10
. The header
20
contains control information for the data
30
and other information, and the data
30
is the content to be sent from the transmitter to the receiver.
As described above, the tap coefficients of the equalization filter are set by using the training sequence
10
. However, this does not mean that it is not necessary to perform any correcting operations during subsequent reception of the header
20
and the data
30
. That is, even in a room, the state of a transmission path (propagation characteristics) is varied by, for instance, movement of a person at a slower rate than a symbol rate (data transmission rate). When the propagation characteristics vary in this manner, the tap coefficients of the equalization filter need to be varied accordingly. Therefore, calculation for updating the tap coefficients of the equalization filter is performed even during reception of the header
20
and the data
30
. But the volume of this calculation is enormous. For example, where a recursive least square (RLS) algorithm, which is considered a high-convergence, stable adaptive algorithm, in complex number form, k(7k+6) times of multiplications are needed for k-stage filter taps. If k is 7 and the symbol rate is 10 MHz, a computing ability of 3.85 GIPS is needed. In practice, it is problematic to perform such calculation during reception of the header
20
and the data
30
, and even the training sequence
10
.
Therefore, as a realistic measure, an adaptive algorithm that is poor in characteristics but simple is used, or high-speed sampling is performed and a head portion of symbols is used which is free of intersymbol interference. However, as the transmission rate increases, these techniques can no longer be accommodated and it becomes more necessary to use an algorithm, such as the RLS algorithm, that requires a very high computing ability.
To improve the convergence in executing an adaptive algorithm as mentioned above, it is better that data to be transmitted and received is whitened. “Whitened” means that it is flat over the entire frequency range. This is because if the adaptive operation is performed for the reception data having a deviation, tap coefficients may vary in an undesired direction to cause a reception error. Usually, the header
20
and the data
30
are also whitened by, for instance, scrambling that uses an LFSR (linear feedback shift register) or the like.
Published Unexamined Patent Application (PUPA) No. 7-162361 discloses use of an adaptive algorithm for the header
20
and the data
30
as mentioned above. However, this reference has no disclosure as to a signal-like nature of the header
20
and the data
30
. PUPA No. 5-145452 discloses dividing a single, long unique word into a plurality of parts and inserting those into a data portion. This purpose is to synchronize with each data part by using each part of the unique word. In addition, usually a unique word has only a minimum necessary length because a long, redundant unique word decreases a data transmission amount. It is doubtful whether each part obtained by dividing a unique word into a plurality of parts in the manner as disclosed in the Published Unexamined PUPA No. 5-145452 has a certain meaning. Further, where divided parts are meaningful only as a whole, it is necessary to process a unique word after receiving the entire data, storing it in a buffer, receiving all the divided parts of the unique word, and setting tap coefficients.
As described above, there exists no effective method of reducing the calculation volume of tap coefficients tracking operation after tap coefficients of an equalization filter have been set by using a training sequence.
SUMMARY OF THE INVENTION
An object of the subject invention is therefore to reduce the calculation volume of tap coefficients tracking operation.
Another object of the invention is to enhance whiteness of data by using a whitened version of a signal that is used for tap coefficients tracking operation.
To attain the above objects and remedy problems with the prior art, the subject invention provides a wireless communication apparatus comprising frame generating means for generating a frame including a training sequence and a mixed data sequence in which a symbol of a whitened sequence is dispersively inserted into a data sequence; and means for converting the frame into a wireless signal, and for transmitting the wireless signal. With this configuration, a signal in the data sequence is whitened and, in a reception-side wireless communication apparatus, tap coefficients can be updated without causing deviation because an adaptive operation is performed on a whitened sequence. Further, the dispersive insertion allows reduction of the computing ability.
With the above transmission-side wireless communication apparatus, there is used, in the reception side, a wireless communication apparatus comprising receiving means for receiving a wireless signal of a frame including a training sequence and a mixed data sequence in which a symbol of a whitened sequence is dispersively inserted into a data sequence; an equalization filter connected to the receiving means; adaptive operation means for setting tap coefficients of the equalization filter by using the training sequence in the frame; and tracking means for performing an adaptive operation by using the respective symbols of the whitened sequence in the frame during reception of the mixed data sequence, and thereby updating the tap coefficients of the equalization filter.
There may be conceived a configuration in which the above-mentioned whitened sequence is a training sequence. Since the training sequence is a signal that is not only known in both the transmission and reception sides but is also whitened, the tracking operation is simplified.
The tracking means may comprise means for detecting, for each symbol of the whitened sequence in the frame, an error between a first value obtained through the equalization filter and a second value that would have been transmitted to this apparatus and is predicted from said first value; and means for updating the tap coefficients of the equalization filter by using the error. That is, even if the whitened sequence is known in neither the transmission side nor the reception side, an error can be detected because tap coefficients of the equalization filter have been set by using the training sequence located at the head of the frame.
Further, there may be conceived a configuration in which the tracking means comprises comparing means for comparing, for each symbol of the training sequence as the whitened sequence in the frame, a first value obtained through the equalization filter and a second value of a corresponding symbol of the training sequence; and means for updating the tap coefficients of the equalization filter by using a result of the comparison.
The above-mentioned frame generating means may comprise means for inserting n symbol of the whitened sequence for every m symbols of the mixed
Ishikawa Hiroshi
Kanada Yoshihisa
IBM Corporation
Luther William
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