WO2002003635A2

WO2002003635A2 - Two-step equaliser for receiving station and associated method

Info

Publication number: WO2002003635A2
Application number: PCT/IB2001/001143
Authority: WO
Inventors: Jun Han
Original assignee: Nokia Networks Oy; Nokia Inc.
Priority date: 2000-07-05
Filing date: 2001-06-27
Publication date: 2002-01-10
Also published as: AU2001266258A1; WO2002003635A3

Abstract

Equalizer apparatus (36), and an associated method, for equalizing a data sequence transmitted upon a communication channel (14) susceptible to distortion. The equalizer (36) equalizes a first portion of the sequence of data in a manner (46) which exhibits high levels of convergence, and the equalizer (36) is trained responsive to the equalization of the first portion of the sequence of data. Then, a second portion of the sequence of data is equalized pursuant to an equalization process (48) which exhibits a reduced level of computational complexity for its effectuation. Thereby, equalization is performed relatively quickly and also relatively accurately.

Description

EQUALIZER, AND ASSOCIATED METHOD THEREFOR, FOR A

RECEIVING STATION

The present invention relates generally to a manner by which to equalize a digital signal provided to a communication station, such as a receive signal sent to a base station of a cellular communication system. More particularly, the present invention relates to an equalizer which equalizes one portion of the digital signal in a manner which exhibits good convergence characteristics, thereby to train the equalizer, and which thereafter equalizes another portion of the digital signal in a manner which exhibits reduced levels of computational complexity.

BACKGROUND OF THE INVENTION

A communication system is formed, at a minimum, of a sending station and a receiving station interconnected by a communication channel. Data to be communicated by the sending station to the receiving station is converted, if necessary, into a form to permit its communication upon the communication channel . A communication system can be defined by almost any combination of sending and receiving stations including, for instance, circuit board- positioned elements as well as more conventionally- defined communication systems used by spaced-apart users to communicate data therebetween.

When data communicated upon a communication channel is received at the receiving station, the receiving station acts upon, if necessary, the received data to recreate the informational content thereof. In an ideal communication system, the data, when received at the receiving station, is identical to the data when transmitted by the sending station. However, in an actual communication system, the data is distorted during its communication upon the communication channel. Such distortion distorts values of the data when received at the receiving station. If the distortion is significant, the informational content of the data, as transmitted, cannot be recovered. A radio communication system is exemplary of a communication system utilized to communicate data between sending and receiving stations. In a radio communication system, the communication channel is formed of a radio communication channel. A radio communication channel is defined upon a portion of the electromagnetic spectrum. In a wireline communication system, in contrast, a physical connection extending between the sending and receiving stations 'is required to form the communication channel. Communication of data upon a radio communication channel is particularly susceptible to distortion due, in part, to the propagation characteristics of the radio communication channel. Data communicated on conventional wireline channels are also, however, susceptible to distortion in manners analogous to the manner by which distortion is introduced upon the data communicated in a radio communication system.

Digital communication techniques have been implemented in radio, as well as other, communication systems. Digital communication techniques generally permit the communication system in which the techniques are implemented to achieve greater communication capacity contrasted to conventional, analog communication techniques. In a communication system which utilizes digital communication techniques, information which is to be communicated is digitized to form digital bits. The digital bits are typically formatted according to a formatting scheme. Groups of the digital bits, for instance, are positioned to form a packet of data.

Multi-path transmission of the data upon a radio, or other, communication channel introduces distortion upon the data as the data is actually communicated to the receiving station by a multiple number of paths. The data detected at the receiving station, as a result, is the combination of signal values of data communicated upon a plurality of communication paths. Intersymbol interference and Rayleigh fading causes distortion of the data. Such distortion, if not compensated for, prevents the accurate recovery of the transmitted data.

Various manners are used to compensate for the intersymbol interference and Rayleigh fading. Equalizer elements, for instance, are utilized to recreate a symbol sequence believed to be transmitted by a sending station based upon values of the symbols when received at the receiving station. Equalizers are regularly implemented through execution of algorithms by a processing device. Performance of an equalizer is characterized in terms of convergence, tracking, and computational complexity. A well- performing equalizer exhibits high convergence levels, good tracking performance, all while requiring relatively low levels of computational complexity. However, equalizer algorithms which exhibit high levels of convergence and good tracking performance generally require high levels of computational complexity. And, algorithms requiring only low levels of computational complexity generally exhibit relatively poor levels of convergence and poor tracing performance . '

When data is communicated at relatively high rates, such as during operation of a cellular communication system, high levels of computational complexity are not able to perform the necessary computations to equalize symbol sequences quickly enough to maintain the necessary data throughput rates .

If a manner could be provided by which better to equalize a symbol sequence, thereby to provide an equalizer which exhibits high levels of convergence and .good tracking performance while limiting the computational complexity required to equalize the symbol sequence, improved communication of data would be permitted.

It is in light of this background information related to the communication of digital data that the significant improvements of the present invention have evolved .

SUMMARY OF THE INVENTION

The present invention, accordingly, advantageously provides apparatus, and an associated method, by which to equalize a digital signal provided to a communication station by way of a communication channel susceptible to distortion.

During operation of an embodiment of the present invention, one portion of a digital signal is equalized in a first manner which exhibits good convergence characteristics, thereby to train an equalizer at which the digital signal is equalized.

Thereafter, another portion of the digital signal is equalized in a manner which exhibits reduced levels of computational complexity, thereby permitting equalization of such portions more quickly than equalization of the first portion. By training the equalizer through equalization of the first portion of the digital signal in manner which exhibits the good convergence characteristics, the equalizer effectively becomes "pre-equalized" so that subsequent portions of the digital signal can be equalized effectively in a non-computationally-intensive manner. The advantages of equalizing a signal in_, a manner which exhibits good convergence and tracking performance is provided while also permitting equalization of the signal relatively quickly. In one aspect of the present invention, the first portion of digital signal is equalized utilizing a RLS (Recursive Least-Squares) process. The RLS process exhibits good levels of convergence and tracking performance but requires a relatively high level of computational complexity to perform the equalization process. The results obtained during the equalization process are used to set tap values of an equalizer, prior to subsequent equalization operations.

In another aspect of the present invention, the other portion of the digital signal is equalized through utilization of a Least-Mean-Square (LMS) process. The LMS process is relatively computationally non-complex. While the LMS process generally exhibits poorer levels of convergence and tracking performance, because the taps of an equalizer at which equalization is to be performed are already set through prior operation of the equalizer pursuant to the RLS process, performance of the LMS process is well able to perform equalization of the portion of the digital signal applied thereto. And, because the LMS process is relatively computationally non-complex, the equalization of the other portion of the digital signal is performed relatively quickly. In another aspect of the present invention, a digital signal is applied to an equalizer to be equalized thereat. The digital signal is formatted to form a series of digital symbols which are subdivided into sets of digital symbols according to a formatting scheme. One of the sets of the sequence of symbols forms a training sequence, and at least one other of the sets of the symbol sequence forms informational data. The training sequence is of a prescribed set of values, the prescribed set of values being known. When the digital signal is transmitted upon a channel susceptible to distortion, however, the symbols of the training sequence are susceptible to distortion, caused, for instance, by intersymbol interference and Rayleigh fading. New training sequences provided to an equalizer at which equalization is performed pursuant to the RLS process . The taps of the equalizer are set responsive to equalization of the training sequence. Then, the set of symbols forming the informational content is provided to the equalizer at which equalization is performed utilizing the LMS process. Responsive to effectuation of the equalization, an equalized representation of the symbols forming the informational content is generated . In one implementation, an equalizer is provided for a receiving station operable in a cellular, or other radio, communication system. The equalizer is provided, for instance, to a base station operable in an EDGE system. Digital signals formatted according to a formatting scheme includes a training sequence and an informational portion. When received at the receiving station, the sequence is buffered at a buffer device. The training sequence forming a portion of the received signal is retrieved from the buffer and equalized by a equalizer pursuant to a RLS process. The taps of the equalizer are set, i.e., trained, responsive to performance of the equalization process. Thereafter, the informational sequence is retrieved from the buffer and equalized at the equalizer pursuant to a LMS process. Because the taps of the equalizer are set pursuant to equalization of the training sequence by the RLS process, equalization utilizing the LMS process generates an equalized signal which exhibits good levels of convergence and tracking performance.

In these and other aspects, therefore, an equalizer is provided for a communication station operable at least to receive a sequence of data communicated to the communication station. The data is communicated to the communication station upon a channel susceptible to distortion. The equalizer equalizes the sequence of data to counteract the distortion introduced thereon. The sequence of data is formatted into a first sequence portion and at least a second sequence portion. A first equalizer element is coupled to receive indications of the first sequence portion of the sequence of data. The first equalizer element operates upon the first sequence portion in a first manner and forms a first-equalized signal responsive thereto. A second equalizer element is coupled to receive indications of the second sequence portion of the sequence of data. The second equalizer element operates upon the second sequence portion in a second manner and forms a second equalized signal responsive thereto. The second equalized signal is equalized to counteract for the distortion introduced upon the data communicated upon the channel susceptible to distortion.

A more complete appreciation of the present invention and the scope thereof can be obtained from the accompanying drawings which are briefly summarized below, the following detailed description of the presently-preferred embodiments of the invention, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a functional block diagram of a communication system in which an embodiment of the present invention is operable.

Figure 2 illustrates a sequence of data communicated during operation of the communication system shown in Figure 1 and of which at least portions thereof are equalized during operation of an embodiment of the present invention.

Figure 3 illustrates a functional block diagram of a Decision Feedback Equalizer (DFE) utilized in an exemplary implementation of an embodiment of the present invention. Figure 4 illustrates a method flow diagram listing the method of operation of an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Turning first to Figure 1, a communication system, shown generally at 10, is operable to communicate data between communication stations. In the exemplary implementation, the communication system forms a radio communication system, here a cellular communication system. It should be understood at the outset, however, that in other implementations operation of an embodiment of the present invention is analogously effectuable. Analogous description of operation of an embodiment of the present invention can similarly be made with respect to its implementation in such other communication systems. The communication system 10 is here shown to include a mobile station 12 operable to communicate data by way of a radio link 14 with a base transceiver station 16. Data originated at the mobile station is communicated upon a reverse link, or uplink, channel of the radio link to the base transceiver station.

And, data originated at the base transceiver station is communicated upon a forward link, or downlink, channel of the radio link to the mobile station. Two- way communications are thereby effectuated between the base transceiver station and the mobile station by communication of data on the forward and reverse link channels, respectively.

The mobile station 12 includes a transmit portion 18 for transmitting data to be communicated upon the reverse link to the base transceiver station and a receive portion 22 for receiving data communicated to the mobile station upon a forward link channel.

Communication of data upon the radio link 14 is susceptible to distortion caused, for instance, by multi-path propagation and Rayleigh fading. Data communicated upon the radio link, as a result, differs when received at a receiving station than the sending station from which the data originates. For instance, data communicated by the mobile station 12 to the base transceiver station 16 upon a reverse link channel susceptible to distortion differs in value, when received at the base transceiver station, from the corresponding data when transmitted by the mobile station. In order to recover the informational content of the data, the distortion introduced upon the data must be removed, or otherwise compensated for.

The base transceiver station includes a transmit portion 24 and a receive portion 26. The transmit portion is operable to generate and transmit data to be communicated upon a forward link channel to the mobile station. And, the receive portion is operable to receive data communicated to the base transceiver station upon reverse link channels. The receive portion of the base transceiver station is here shown to include a demodulator and down converter 28 coupled to an antenna transducer 32 of the base transceiver station. The antenna transducer 32 is operable to convert, out of electromagnetic form, and into electrical form, data-containing signals transmitted upon the reverse link channels and received at the base transceiver station. The electrical signals are demodulated and down-converted to a baseband frequency by the demodulator and down-converter. A baseband signal is generated on the line 34 and is provided to an equalizer 36 of an embodiment of the present invention .

The equalizer is operable to equalize the baseband signal provided thereto in a manner which corrects for the distortion introduced upon the signal containing the data during its transmission upon the radio link 14. While the equalizer 36 is shown in functional block form in the figure, in the exemplary implementation, the equalizer is implemented at a processing device.

The equalizer 36 includes a buffer element 38 coupled to the line 34. The buffer is operable to buffer successive portions of the baseband signal generated on the line 34. Selected portions of the buffered signal are provided by way of the line 42 to a DFE (Decision Feedback Equalization) operator 44. The DFE operator is here shown further to be coupled to a Recursive Least-Squares (RLS) element 46 and a Least-Mean-Square (LMS) element 48.

The DFE operator 44 performs equalization upon the data portion retrieved from the buffer 38 according to a selected one of the RLS and LMS processes defined by the elements 46 and 48, respectively.

In the exemplary implementation, a first portion of the baseband data signal stored at the buffer 38 is retrieved and equalization is performed by the operator 44 pursuant to a RLS process. The RLS process permits equalization to be performed upon the data in a manner which exhibits high levels of convergence and data tracking. However, the RLS process exhibits a relatively high computational requirement and utilizes complex program structures for its effectuation. The results of the equalization performed pursuant to the RLS process permits the DFE operator to be trained. That is to say, the tap values of taps forming portions of the DFE operator are set through equalization performed upon the first portion of the buffer data pursuant to the RLS process. Because of the high levels of convergence exhibited by the RLS process, setting of the tap values of the DFE operator 44 in this manner ensures that relatively accurate tap values are selected.

Subsequently, a second portion of the baseband data signal buffered at the buffer 38 is retrievable and is provided to the DFE operator subsequent to setting of the tap values thereat. Equalization is performed at the DFE operator pursuant to the LMS process. The LMS process requires only relatively little computational complexity and, as a result, equalization is effectuated fairly quickly. While the LMS process exhibits relatively low levels of convergence and tracking performance, because the tap values are set prior to performance of the LMS process with performance of a LRS process, problems which might otherwise occur as a result of the convergence and tracking characteristics of the LMS process are not evidenced.

An equalized signal equalized through operation of the equalizer 36 is provided on the line 52 to a decoder 54. Decoding operations are performed thereat. The base transceiver station is, in turn, coupled by way of the line 56 to a Base Station Controller (BSC) 58. And, in turn, the base station controller 58 is coupled to a mobile switching center 62 which is coupled to a PSTN (Public-Switched,

Telephonic Network) 64. A communication station 66 is coupled to the PSTN, and a communication path is formable between the mobile station 12 and the communication 66 by way of the radio link 14 and the various structure of network infrastructure forming the fixed network of the communication system.

Because selected portions of the signal received at the base transceiver station are equalized in manners which exhibit high levels of convergence and tap values of the DFE operator are set therefrom, operation of the equalizer 36 is caused to exhibit high levels of convergence. And, because portions of a signal equalized at the equalizer other than the first portion are equalized utilizing a LMS process, the equalization is performed relatively quickly.

While operation of equalization pursuant to an embodiment of the present invention is described with respect to the equalizer 36 forming a portion of the base transceiver station, analogous functional elements can also be embodied at the receive portion 22 of the mobile station 12. And, more generally, the functions performed by the equalizer 36 can be utilized pursuant to the teachings of an embodiment of the present invention by almost any receiving station operable to receive digital signals transmitted upon a communication channel susceptible to multi-path propagation and Rayleigh fading.

In the exemplary implementation in which the communication station 10 forms a cellular communication system, the equalizer 36 advantageously forms a portion a base transceiver station operable in an EDGE system. In EDGE system, data is formatted to permit its communication in a TDMA (Time-Division, Multiple Access) time slot.

Figure 2 illustrates the formatting scheme by which data is formatted for communication in such an EDGE system. A frame 72 of data is shown in the figure. The frame includes a first portion 74 containing 8.25 guard symbols, a second portion 76 containing three tail symbols, a data portion 78 containing 57 symbols, a portion 82 containing training symbols, another data portion 84 containing 57 data symbols, and a final portion 86 containing three tail symbols. A frame is transmitted during a time slot allocated to the sending station, here, for instance, the mobile station 12. The frame is communicated upon the radio link 14 and during its transmission, and the data contained in the frame is distorted due to multi-path fading and Rayleigh fading. The frame, when detected at the antenna transducer 32 of the base transceiver station, as a result, includes component portions which are distorted due to the fading. The frame is processed upon by the demodulator and down converter 28 and, thereafter, the frame, in baseband form, is provided to the buffer 38. The entire frame, or at least the training symbols 82 and the data symbols of the portion 78 and 84, are buffered at the buffer 38.

First, the training symbols 82 are retrieved from the buffer and applied to the DFE operator 44, equalized thereat pursuant to the RLS process . The number of training symbols is 26, and the equalization thereof pursuant to the RLS process is relatively quick, albeit requiring high levels of computational complexity, due to the relative shortness of the number of training symbols.

The tap values of the taps of the DFE operator are then set. Thereafter, the data symbol portions 78 and 84 are retrieved from the buffer and equalized at the DFE operator 44. The data portions are equalized by a LMS process whichl is able to be performed quickly due to the relatively low computational complexity thereof and also accurately due to the setting of the tap values by the earlier-performed RLS process. Thereby, the informational content of the frame of data, namely, the data sequence portions 78 and 84, are equalized to remove distortion introduced thereon during transmission of the frame upon the radio link. Because of the relative quickness at which the equalization is performed, the high transmission rates at which the EDGE system is to be operable is maintained.

Figure 3 illustrates the DFE operator forming a portion of the equalizer 36 shown in Figure 1. The DFE operator includes a feed forward filter portion 92 and a feedback filter portion 94. The feed forward filter includes a plurality of series-connected delay elements, T_p 96. And, tap elements 98 are variously connected to input and output sides of the delay elements 96. Each of the tap elements 98 has associated therewith a tap value by which signals applied thereto are multiplied. Product values generated by each of the tap elements are provided to a summing element 102, operable to sum the values provided theretogether . The tap values associated with each of the tap elements are provided to the respective tap elements by way of the lines 104.

The feedback filter portion 94 analogously also includes a plurality of delay elements 106 and a plurality of tap elements 108. Each of the tap elements has associated therewith a tap value. The tap values are then selectable, here by way of the lines 104. Products formed by each of the tap elements 108 are provided to the summer 102 to be summed together thereat with the products formed through operation of the tap elements 98 of the feed forward filter portion. Summed values formed by the summer 102 are provided to a decision device 112, the results of which are generated on the line 52.

The DFE operator 44 further includes a switch element 114 which provides for alternate, switch connection to receive the training sequence stored at the buffer 38 (shown in Figure 1) and here represented by the training sequence block 116. The switch element 114 is also selectably connectable to receive the results of the decision device 112. A second side of the switch element extends to an error calculator element 118 and also to a first delay element 106 of the feedback filter portion 94. When the switch element is connected, as shown in the Figure, to receive the training sequence 116, the DFE operator equalizes the training sequence pursuant to the RLS process. Once completed, the tap values of the tap elements 98 and 108 are controlled by way of the lines 104. Once the tap values of the tap elements are set, the switch element is switched into a second switch position and the data sequence portions are retrieved from the buffer 38 (shown in Figure 1) on the line 42 and provided to the feed forward filter portion 92. Equalization is performed pursuant to the LMS process, and equalized results are generated on the line 52.

Figure 4 illustrates a method flow diagram, shown generally at 112, operable to equalize a sequence of data to counteract distortion introduced thereon when the data is communicated upon a channel susceptible to distortion.

First, and as indicated by the block 128, a first sequence portion of the sequence of data is equalized by operating upon the first sequence, portion in a first manner. Then, and as indicated by the block 132, a first-equalized signal is formed responsive thereto .

Then, and as indicated by the block 134, a second sequence portion of the sequence of data is equalized by operating upon the second sequence portion in a second manner. Then, and as indicated by the block 136, a second-equalized signal is formed responsive thereto. The second-equalized signal is equalized to counteract for the distortion introduced upon the data when transmitted upon the channel susceptible to distortion.

The preferred descriptions are of preferred examples for implementing the invention, and the scope of the invention should not necessarily be limited by this description. The scope of the present invention is defined by the following claims.

Claims

We claim :

1. In a communication station operable at least to receive a sequence of data communicated to the communication station upon a channel susceptible to distortion, an improvement of an equalizer for equalizing the sequence of data to counteract the distortion introduced thereon, the sequence of data formatted into a first sequence portion and at least a second sequence portion, said equalizer comprising: a first equalizer element coupled to receive indications of the first sequence portion of the sequence of data, said first equalizer element for operating upon the first sequence portion in a first manner and for forming a first-equalized signal responsive thereto; and a second equalizer element coupled to receive indications of the second sequence portion of the sequence of data, said second equalizer element for operating upon the second sequence portion in a second manner and for forming a second-equalized signal responsive thereto, the second-equalized signal equalized to counteract for the distortion introduced thereon .

2. The equalizer of claim 1 wherein the first manner in which said first equalizer element operates upon the first sequence portion exhibits a first convergence level and wherein the second manner in which said second equalizer element operates upon the second sequence portion exhibits a second convergence level, the first convergence level greater than the second convergence level .

3. The equalizer of claim 2 wherein said first equalizer element performs operations of a recursive least-sequence (RLS) equalization process.

4. The equalizer of claim 3 wherein said second equalizer element performs operations of a least-mean- square (LMS) equalization process.

5. The equalizer of claim4 wherein said equalizer further comprises an equalizer filter at which the operations of the RLS equalization process of said first equalizer element are performed, said equalizer filter including tap elements having selectable tap element values, the first equalized signal of values to cause selection of the tap element values .

6. The equalizer of claim 5 wherein the operations of the LMS equalization process of said second equalizer are performed at said equalizer filter subsequent to selection of the tap element values responsive to operation of the RLS equalization process of said first equalizer element.

7. The equalizer of claim 6 wherein said equalizer filter comprises a nonlinear device.

8. The equalizer of claim 7 wherein said equalizer filter comprises a decision feedback equalizer.

9. The equalizer of claim 1 further comprising a buffer coupled to receive representations of the sequence of data, said buffer for buffering the representations of the sequence of data, and wherein the indications of the first sequence portions to which said first equalizer element is coupled to receive and of the second sequence portions to which said second equalizer element is coupled to receive are provided thereto by said buffer.

10. The equalizer of claim 1 wherein the first sequence portion into which the sequence of data is formatted comprises a first group of symbols forming a training sequence and wherein said first equalizer element operates upon the training sequence to form the first-equalized signal.

11. The equalizer of claim 1 wherein the second sequence portion into which the sequence of data is formatted comprises a second group of symbols forming a data sequence and wherein said second equalizer element operates upon the data sequence to form the second-equalized signal.

12. The equalizer of claim 1 wherein the first sequence portion is of a first symbol length, wherein the second sequence portion is of a second symbol length, the second symbol length greater than the first symbol length, wherein the first manner by which said first equalizer element operates upon the first sequence portion is of a first computational complexity, and wherein the second manner by which said second equalizer element operates upon the second sequence portion is of a second computational complexity, the second computational complexity less than the first computational complexity.

13. The equalizer of claim 1 wherein the communication station comprises a radio receiver, wherein the channel susceptible to distortion comprises a radio channel susceptible to ISI (Inter Symbol Interference) , and wherein the second-equalized signal formed by said second equalizer element is equalized to counteract for the ISI.

14. The equalizer of claim 13 wherein the radio receiver comprises a receive portion of a base transceiver station of a radio communication system operable pursuant to an EDGE system, wherein said equalizer comprises a processing device and wherein said first equalizer element and said second equalizer element each comprise algorithms executable by said processing device.

15. In a method for receiving a sequence of data communicated to a communication station upon a channel susceptible to distortion, an improvement of a method for equalizing the sequence of data to counteract the distortion introduced thereon, the sequence of data formatted into a first sequence portion and at least a second sequence portion, said method comprising: operating upon the first sequence portion in a first equalization manner to form a first-equalized signal responsive thereto; and operating upon the second sequence in a second equalization manner to form a second-equalized signal responsive thereto, the second-equalized signal equalized to counteract for the distortion introduced thereon.

16. The method of claim 15 wherein the first equalization manner upon which the first sequence portion is operated during said operation of operating upon the first sequence portion exhibits a first convergence level and wherein the second equalization manner upon which the second sequence portion is operated during said operation of operating upon the second sequence portion exhibits a second convergence level, the fist convergence level greater than the second convergence level.

17. The method of claim 15 wherein the first sequence portion is of a first symbol length, wherein the second sequence portion is of a second symbol length, the second symbol length greater than the first symbol length, wherein the first equalization manner upon which the first sequence portion is operated during said operation of operating upon the first sequence portion is of a first computational complexity, and wherein the second equalization manner upon which the second sequence portion is operated during said operation of operating upon the second sequence portion is of a second computational complexity, the second computational complexity less than the first computational complexity.

18. The method of claim 15 wherein the first equalization manner upon which the first sequence portion is operated during said operation of operating upon the first sequence portion comprises a recursive least-squares (RLS) process.

19. The method of claim 15 wherein the second equalization manner upon which the second sequence portion is operated during said operation of operating upon the second sequence portion comprises a least- mean-square (LMS) equalization process.

20. The method of claim 15 wherein said operation of operating upon the first sequence portion and of operating upon the second sequence portion are performed at a decision feedback equalizer.