WO2015172355A1

WO2015172355A1 - Pre-coded mimo transmissions for ethernets

Info

Publication number: WO2015172355A1
Application number: PCT/CN2014/077559
Authority: WO
Inventors: Danlu Zhang; Yin Huang; Bin Tian
Original assignee: Qualcomm Incorporated
Priority date: 2014-05-15
Filing date: 2014-05-15
Publication date: 2015-11-19
Also published as: WO2015172548A1

Abstract

A method of pre-coding MIMO signals for concurrent transmission over a plurality of twisted pairs is disclosed. A channel estimation is determined based, at least in part, on interference attributable to a number 2N of conductors that form N twisted pairs, wherein N is an integer greater than or equal to 2. For some embodiments, a set of test signals may be transmitted, via the N twisted pairs, from a first device to a second device, and the channel estimation may be received, based on the set of test signals, from the second device. At least 2N-1 data streams are pre-coded, based on the channel estimation, to be concurrently transmitted over the N twisted pairs. For some embodiments, 2N test signals may be pre-coded to be concurrently transmitted over the N twisted pairs.

Description

PRE-CODED MIMO TRANSMISSIONS FOR ETHERNETS

TECHNICAL FIELD

[0001 ] The present embodiments relate generally to twisted pairs composed of multiple wires, and specifically to multiple-input and multiple- output (MIMO) signal transmission using twisted pairs.

BACKGROUND OF RELATED ART

[0002] A twisted pair is a physical communication medium having two balanced conductors (e.g., wires) that can be used to carry current (e.g., data signals). Having two balanced conductors allows the twisted pair to be used for transmitting differential signals, while the twisting of the two conductors helps cancel electromagnetic interference. Electrical cables used in communications systems are typically composed of one or more twisted pairs. Some electrical cables are further encapsulated by an outer shield which may shield the inner conductors from external sources of interference.

[0003] Because twisted-pair cables are relatively inexpensive, they are widely used in modern high-speed differential signal transmission applications. For example, Category 5 (Cat 5) cables, comprising 4 or more twisted pairs, are typically used in 10BASE-T, 100BASE-TX, and 1000BASE-T Ethernet systems. Category 6 (Cat 6) cables, which are backwards compatible with Cat 5 cables, can be used for up to 10GBASE-T Ethernet systems. While the twisting of the conductors, coupled with differential signaling techniques, helps mitigate interference (e.g., noise, cross-talk, etc.) between twisted pairs, such

interference may still create a bottleneck at higher signal-to-interference-plus- noise (SINR) ratios.

SUMMARY

[0004] This Summary is provided to introduce in a simplified form a selection of concepts that are further described below in the Detailed

Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter.

[0005] A method and apparatus for concurrently transmitting multiple data signals over multiple twisted pairs is disclosed. A channel estimation is first determined based on interference attributable to a number 2N of conductors that form N twisted pairs (e.g., for N > 2). At least 2N-1 data streams are then pre-coded, based on the channel estimation, to be concurrently transmitted over the N twisted pairs. The pre-coding is to mitigate the interference on the 2N conductors. For some embodiments, the pre-coded data streams may be transmitted as discrete multi-tone (DMT) signals.

[0006] The channel estimation may be determined by transmitting a set of test signals, via the N twisted pairs, from a first device to a second device. The channel estimation may then be received, based on the set of test signals, from the second device. For some embodiments, 2N-1 test signals are transmitted, concurrently over the N-twisted pairs. For example, each of the 2N- 1 test signals may be transmitted on a separate one of a group of 2N-1 of the conductors, wherein another of the conductors comprises a common return path. For other embodiments, 2N test signals are transmitted, concurrently, over the N twisted pairs. For example, each of the 2N test signals may be transmitted on a separate one of the 2N conductors, wherein a conductive shield for the N twisted pairs comprises a common return path.

[0007] For some embodiments, a pre-coding matrix may be generated based on the channel estimation and applied to each of the 2N-1 data streams to be transmitted. Further, for some embodiments, 2N data streams may be pre- coded to be transmitted, concurrently, over the N twisted pairs. For example, each of the 2N data streams may be transmitted on a separate one of the 2N conductors, wherein a conductive shield for the N twisted pairs comprises a common return path.

[0008] In other embodiments, a communications device transmits a set of negotiation data, via a number N of twisted pairs, to a receiving device (for N > 2). The communications device subsequently receives a response from the receiving device, and determines a number of data signals to be concurrently transmitted over the N twisted pairs based, at least in part, on the response. For some embodiments, the communications device may transmit at least 2N-1 test signals, concurrently, over the N twisted pairs.

[0009] The communications device may further transmit N data signals, concurrently, over the N twisted pairs when the response does not include a confirmation of receipt of the at least 2N-1 test signals. Otherwise, when the response includes a confirmation of receipt of the at least 2N-1 test signals, the communications device may transmit at least 2N-1 data signals, concurrently, over the N twisted pairs.

[0010] For some embodiments, the response may include a channel estimation based, at least in part, on interference attributable to 2N conductors that form the N twisted pairs. The communications device may further determine whether to pre-code the 2N-1 data signals based on the channel estimation.

[001 1 ] Further, for some embodiments, the communications device may transmit the set of negotiation data using DMT modulation techniques. Then, based on the response from the receiving device, the communications device may determine whether to also transmit the data signals using DMT modulation techniques.

[0012] Accordingly, the various signal transmission techniques described herein with respect to the exemplary embodiments may provide higher data rates across multiple twisted pairs than conventional data transmission techniques. In addition, at least some of the present embodiments may mitigate cross-talk and/or other interference among twisted pairs to ensure that data is reliably and accurately transmitted across a communications channel. Using DMT modulation techniques may further allow for simpler receiver design.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The present embodiments are illustrated by way of example and are not intended to be limited by the figures of the accompanying drawings, where:

[0014] FIGS. 1A-1 B illustrate MIMO transmission configurations for a cable including a set of twisted pairs, in accordance with some embodiments; [0015] FIG. 2 is a block diagram illustrating an embodiment of a MIMO data transmission system with pre-coding functionality.

[0016] FIG. 3 is an illustrative flow chart depicting an exemplary operation for pre-coding MIMO signals in accordance with some embodiments.

[0017] FIG. 4 is an illustrative flow chart depicting a more detailed embodiment of a MIMO pre-coding operation.

[0018] FIG. 5 is a block diagram illustrating an embodiment of a MIMO data transmission system employing multiple twisted pairs.

[0019] FIG. 6 is a block diagram illustrating another embodiment of a MIMO data transmission system employing multiple twisted pairs.

[0020] FIG. 7 is a block diagram of a communications device that is configurable to communicate with legacy devices in accordance with some embodiments.

[0021 ] FIG. 8 is an illustrative flow chart depicting an operation for determining a set of communications parameters in accordance with some embodiments.

[0022] FIG. 9 is a block diagram of a communications device in accordance with some embodiments.

DETAILED DESCRIPTION

[0023] In the following description, numerous specific details are set forth to provide a thorough understanding of the present disclosure. Also, in the following description and for purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present embodiments. However, it will be apparent to one skilled in the art that these specific details may not be required to practice the present embodiments. In other instances, well-known circuits and devices are shown in block diagram form to avoid obscuring the present disclosure. The term "coupled" as used herein means connected directly to or connected through one or more intervening

components or circuits. Any of the signals provided over various buses described herein may be time-multiplexed with other signals and provided over one or more common buses. Additionally, the interconnection between circuit elements or software blocks may be shown as buses or as single signal lines. Each of the buses may alternatively be a single signal line, and each of the single signal lines may alternatively be buses, and a single line or bus might represent any one or more of a myriad of physical or logical mechanisms for communication between components.

[0024] FIG. 1A illustrates a MIMO transmission configuration l OOA for a cable including a set of twisted pairs 150 and 160, in accordance with some embodiments. The first twisted pair 150 includes conductors 101 and 102, and the second twisted pair 160 includes conductors 103 and 104. For some embodiments, the twisted pairs 150 and 160 may be shielded by a conductive shield 105. The twisted pairs 150 and 160 are coupled between a transmitter 1 10 and a receiver 120. The transmitter 1 10 includes a number of voltage sources 1 12, 1 14, and 1 16. For some embodiments, the first voltage source 1 12 is coupled to the conductors 101 and 102, the second voltage source 1 14 is coupled to the conductors 101 and 103, and the third voltage source 1 16 is coupled to the conductors 101 and 104. The receiver 120 includes a number of detector circuits 122, 124, and 126. For some embodiments, the first detector circuit 122 is coupled to the conductors 101 and 102, the second detector circuit 124 is coupled to the conductors 101 and 103, and the third detector 126 is coupled to the conductors 101 and 104.

[0025] A first set of data signals (e.g., corresponding to a first subset of data) may be generated by the first voltage source 1 12 and transmitted over the first twisted pair 150 (e.g., via the conductors 101 and 102). More specifically, the first voltage source 1 12 may apply a first voltage Vi across the conductors 101 and 102. The first voltage Vi is translated into the first set of data signals. The first detector circuit 122 may receive the first set of data signals, via the conductors 101 and 102, by detecting the current and/or voltage across a first load impedance Zi . The first detector circuit 122 may then recover the first data stream based on the detected current(s) and/or voltage(s). For some

embodiments (e.g., wherein the conductors 101 and 102 are substantially symmetrical), the first subset of data may be transmitted on the twisted pair 150 using differential signaling techniques. [0026] A second set of data signals (e.g., corresponding to a second subset of data) may be generated by the second voltage source 1 14 and transmitted via the conductors 101 and 103. Specifically, the second voltage source 1 14 may apply a second voltage V₂ across the conductors 101 and 103. The second voltage V₂ is translated into the second set of data signals. The second detector circuit 124 may receive the second set of data signals, via the conductors 101 and 103, by detecting the current and/or voltage across a second load impedance Z₂. The second detector 124 may then recover the second data stream based on the detected current(s) and/or voltage(s). For some embodiments, the second voltage source 1 14 transmits data signals using one of the conductors of the first twisted pair 150 (e.g., conductor 101 ) and one of the conductors of the second twisted pair 160 (e.g., conductor 103).

[0027] A third set of data signals (e.g., corresponding to a third subset of data) may be generated by the third voltage source 1 16 and transmitted via the conductors 101 and 104. Specifically, the third voltage source 1 16 may apply a third voltage V₃ across the conductors 101 and 104. The third voltage V₃ is translated into the third set of data signals. The third detector 126 may receive the third set of data signals, via the conductors 101 and 104, by detecting the current and/or voltage across a third load impedance Z3. The third detector 126 may then recover the third data stream based on the detected current(s) and/or voltage(s). For some embodiments, the third voltage source 1 16 transmits data signals using the shared conductor of the first twisted pair 150 (e.g., conductor 101 ) and the remaining the conductor of the second twisted pair 160 (e.g., conductor 104).

[0028] Because the conductor 101 is shared by (e.g., coupled to) all three voltage sources 1 12, 1 14, and 1 16, the voltage level of the conductor 101 may be used as a common reference voltage by each of the voltage sources 1 12, 1 14, and 1 16 for generating their respective data signals. For some

embodiments, the conductor 101 may be grounded. For other embodiments, the transmitter 1 10 may include circuitry to selectively control each of the voltage sources 1 12, 1 14, and 1 16 to ensure that the transmission of data by one voltage source does not interfere with the transmission of data by any of the other voltage sources. [0029] Treating the conductors 101 -104 as individual transmission lines provides an additional degree of freedom (e.g., allowing up to 3 data signals to be transmitted in parallel) as compared to, for example, conventional twisted pair transmission techniques that use two conductors to transmit each data signal. Furthermore, architectural similarities between the systems described herein and conventional communications systems may enable the present embodiments to be readily applied to any network that employs twisted-pair cables (e.g., Category 5 and/or Category 6 cables).

[0030] The conductors 101 -104 of the twisted pairs 150 and 160 may be very close in proximity to one another. Thus, cross-talk may be introduced between the channels when transmitting multiple streams of data in parallel. For example, while the twisting of conductors helps mitigate cross-talk within a twisted pair when differential signaling is used, it has little or no effect on reducing cross-talk between single-ended MIMO signals. Furthermore, signal reflections may also be introduced at the connections between the conductors 101 -104 and the transmitter 1 10 and/or receiver 120. Thus, for some

embodiments, the transmitter 1 10 and/or receiver 120 may include impedance matching circuitry to mitigate such sources of signal interference.

[0031 ] For example, as shown in the configuration 100B of FIG. 1 B, the receiver 120 may include additional load impedances 127-129 to mitigate reflections and/or crosstalk in the conductors 101 -104. Specifically, the load 127 has an impedance value of Z12 and is coupled between the conductors 102 and 103, the load 128 has an impedance value of Z23 and is coupled between the conductors 103 and 104, and the load 129 has an impedance value of Z13 and is coupled between the conductors 102 and 104. These load impedances 127- 129, in conjunction with the impedances associated with the detector circuits 122, 124, and 126, may be used to match the impedance of the receiver 120 to the input impedances associated with the conductors 101 -104.

[0032] In addition to impedance matching, advanced receiver and/or transmitter techniques may effectively suppress, or even eliminate, cross-talk between conductors. Examples of such receiver-side techniques include successive interference cancellation (SIC) and linear minimum-mean-square- error (LMMSE). For some embodiments, the transmitter 1 10 may pre-code a set of data signals so that they will be accurately received (and decoded) by the receiver 120 even after cross-talk and/or other interference along the channel has taken effect.

[0033] It should be noted that the present embodiments are described herein with respect to cables composed of two twisted pairs (e.g., twisted pairs 150 and 160) for simplicity only. The enhanced MIMO transmission techniques described herein can be readily applied across any number N of twisted pairs. For example, the configurations 100A and 100B can be easily expanded to transmit 2N-1 data streams across N twisted pairs (e.g., wherein each data stream is transmitted on a respective one of the 2N conductors, and one of the conductors is used as a common return path). Moreover, the N twisted pairs may be physically packaged into one or multiple cables. The shielding of the cables may be formed from a conductive material (e.g., conductive shield 105).

[0034] For some embodiments, up to 2N data streams may be transmitted across N twisted pairs in a shielded cable (e.g., wherein each data stream is transmitted on a respective one of the 2N conductors, and the conductive shielding is used as a common return path). For example, four data streams may be transmitted across the two twisted pairs 150 and 160 by using the conductive shield 105 as an additional signal-carrying conductor. More specifically, a first data signal may be transmitted using the first conductor 101 and conductive shield 105, a second data signal may be transmitted using the second conductor 102 and conductive shield 105, a third data signal may be transmitted using the third conductor 103 and conductive shield 105, and a fourth data signal may be transmitted using the fourth conductor 104 and conductive shield 105.

[0035] FIG. 2 is a block diagram illustrating an embodiment of a MIMO data transmission system 200 with pre-coding functionality. The system 200 includes a transmit (TX) device 210 and a receive (RX) device 220 coupled to one another via the twisted pairs 150 and 160. More specifically, the TX device 210 includes a MIMO encoder 212, a MIMO pre-coder 214, and a transmitter 216. The RX device 220 includes a receiver 222 and a MIMO decoder 224. FIGS. 3 and 4 are illustrative flow charts depicting exemplary operations 300 and 400, respectively, for pre-coding MIMO signals in accordance with some embodiments. FIGS. 3 and 4 are described below with reference to the system 200 of FIG. 2.

[0036] FIG. 3 is an illustrative flow chart depicting an exemplary operation

300 for pre-coding MIMO signals in accordance with some embodiments. With reference, for example, to FIG. 2, the TX device 210 and/or RX device 220 may determine a channel estimation for the system 200 based on interference attributable to 2N conductors (e.g., conductors 101 -104) that form N twisted pairs (e.g., twisted pairs 150 and 160), where N is an integer greater than or equal to 2 (310). The channel estimation (or channel state information) describes how a signal propagates from the TX device 210 to the RX device 220. For example, the channel estimation may indicate how much cross-talk is attributable to one or more pairs of conductors (e.g., conductors 101 and 102, conductors 102 and 103, and/or conductors 103 and 104). As used herein, a "pair of conductors" may have a broader meaning than "twisted pair."

Specifically, a pair of conductors may include two conductors that belong to different twisted pairs (e.g., conductors 102 and 103). For example, the crosstalk between conductors of the same twisted pair (e.g., conductors 101 and 102) may be different than the cross-talk between conductors of different twisted pairs (e.g., conductors 102 and 103).

[0037] For some embodiments, the channel estimation may be

determined based on known channel properties (such as channel quality, crosstalk, noise, and/or other measures of interference). For other embodiments, the TX device 210 and/or RX device 220 may determine the channel estimation based on a set of test signals, communicated via the twisted pairs 150 and 160, by observing the channel effects on such test signals (e.g., as described in greater detail below with respect to FIG. 4).

[0038] The TX device 210 then pre-codes at least 2N-1 data streams, based on the channel estimation, to be concurrently transmitted over the N twisted pairs (320). The pre-coding of the data streams is to mitigate the interference on one or more pairs of conductors of the 2N conductors. For example, the TX device 210 may pre-code a first data stream to be transmitted via conductors 101 and 102. Further, the TX device 210 may pre-code a second data stream to be transmitted via conductors 101 and 103 concurrently with the first data stream. Still further, the TX device 210 may pre-code a third data stream to be transmitted via conductors 101 and 104 concurrently with the first and second data streams. Because the pre-coding effectively suppresses and/or mitigates the effects of cross-talk and other interference between the individual conductors 101 -104, the RX device 220 may easily recover the original data (e.g., simply by sampling the data signals on each of the

conductors 101 -104).

[0039] FIG. 4 is an illustrative flow chart depicting a more detailed embodiment of a MIMO pre-coding operation 400. Referring again to FIG. 2, the TX device 210 initially generates N streams of test data to be transmitted via N twisted pairs (410). The test data may correspond to a predetermined set and/or sequence of data, known to both the TX device 210 and the RX device 220, for configuration purposes. For example, the test data may be stored in memory (not shown for simplicity) provided elsewhere on the TX device 210.

Alternatively, the test data may be received from an external device. For some embodiments, the MIMO encoder 212 may receive the test data as two input data streams 201 (1 ) and 201 (2) that are intended to be transmitted over the twisted pairs 150 and 160, respectively. Each of the data streams 201 (1 ) and 201 (2) may correspond to a differential data signal intended to be transmitted via a respective one of the twisted pairs 150 and 160.

[0040] The TX device 210 further encodes (e.g., converts) the N test streams into a number M of enhanced-MIMO (EM) data streams, where M is less than or equal to 2N (420). For some embodiments, the MIMO encoder 212 may encode the N test streams into 2N-1 EM data streams. For example, the MIMO encoder 212 may encode the two input data streams 201 (1 ) and 201 (2) into three EM data streams 202(1 )-202(3). As described above, with reference to FIGS. 1 A and 1 B, the three EM data streams 202(1 )-202(3) may be transmitted via the conductors 102-104, respectively, wherein conductor 101 is used as a common return path. For other embodiments, the MIMO encoder 212 may encode the N test streams into 2N EM data streams. For example, the MIMO encoder 212 may encode the two input data streams 201 (1 ) and 201 (2) into four EM data streams 202(1 )-202(4). As described above, with reference to FIGS. 1 A and 1 B, the four EM data streams 202(1 )-202(4) may be transmitted via the conductors 101 -104, respectively, wherein the conductive shield 105 is used as a common return path.

[0041 ] The TX device 210 then transmits each stream of EM test data using a respective one of the 2N conductors (430). For some embodiments, no pre-coding is performed during an initial configuration stage. For example, the MIMO pre-coder 214 may be deactivated to allow the EM test data to pass directly through to the transmitter 216. The transmitter 216 may generate data signals representing the EM data by applying a corresponding number of voltages across the conductors 101 -104 and/or conductive shield 105. For some embodiments, the voltage level of one of the 2N conductors may be used as a common reference potential for biasing the remaining three conductors. For example, the transmitter 216 may transmit three EM data streams 202(1 )- 202(3) by applying respective voltage biases between the conductor 101 and each of the remaining conductors 102-104. For other embodiments, the voltage level of a conductive shield may be used as a common reference potential for biasing the remaining conductors. For example, the transmitter 216 may transmit four EM data streams 202(1 )-202(4) by applying respective voltage biases between the conductive shield 105 and each of the conductors 101 -104.

[0042] The RX device 220 subsequently receives the M EM test signals via the N twisted pairs (440). More specifically, the receiver 222 may recover the M EM data streams by detecting (e.g., sampling) the currents and/or voltages transmitted across the conductors 101 -104 and/or a conductive shield surrounding the twisted pairs 150 and 160. For some embodiments, the voltage level of one of the 2N conductors may be used as a reference potential for determining the voltages on each of the remaining 2N-1 conductors. For example, the receiver 222 may receive three EM data streams 204(1 )-204(3) by detecting respective voltage differences between the conductor 101 and each of the remaining conductors 102-104. For other embodiments, the voltage level of the conductive shield 105 may be used as a reference potential for determining the voltages on each of the 2N conductors. For example, the receiver 222 may receive four EM data streams 204(1 )-204(4) by detecting respective voltage differences between the conductive shield 105 and each of the conductors 101 - 104. [0043] The RX device 220 compares the received test signals with the expected values of those test signals to estimate the channel characteristics (450). As described above, the test signals have predetermined data values that are known to both the TX device 210 and the RX device 220. For example, a copy of the test data may be stored in memory (not shown for simplicity) provided elsewhere on the RX device 220. For some embodiments, the receiver 222 may compare the sampled voltages on each of the conductors 101 -104 (and/or conductive shield 105) with expected voltages associated with the corresponding test signals (e.g., EM data 202(1 )-202(4)). For other

embodiments, the receiver 222 may compare the data values of the as-sampled test data (e.g., EM data 204(1 )-204(4)) with corresponding data values for the expected test data (e.g., EM data 202(1 )-202(4)). The receiver 222 may then determine the channel estimation based on the comparison. For example, the channel estimation may be determined by inputting the values for the received test signals (y) and the expected test signals (x) into the equation: y = Hx +n; where y represents a transmit data vector, x represents a receive data vector, H represents a channel estimation matrix, and n is the noise vector.

[0044] The RX device 220 then sends the channel estimation back to the TX device 210 (460). For example, the channel estimation data 206 may be transmitted back across one or more of the conductors 101 -104 (and/or conductive shield 105) from a transmitter (or transceiver) in the RX device 220 (not shown for simplicity). The TX device 210 receives the channel estimation from the RX device 220 (470) and generates a pre-coding matrix based on the channel estimation (480). For example, the channel estimation data 206 may be received by a receiver (not shown for simplicity) in the TX device 210 and forwarded to the MIMO pre-coder 214. The MIMO pre-coder 214 may then generate a pre-coding matrix, to be applied to the EM data, based on the channel estimation. The pre-coding is to counter or suppress the effects of cross-talk and other sources of interference along the channel (e.g., conductors 101 -104) when data is transmitted between the TX device 210 and the RX device 220. Thus, for some embodiments, the pre-coding matrix may

correspond to the inverse of the channel estimation matrix (e.g., H^"1). [0045] For example, the MIMO pre-coder 214 may apply the pre-coding matrix to the set of EM data 202(1 )-202(4) to produce a corresponding set of pre-coded (PC) data 203(1 )-203(4), respectively. The PC data 203(1 )-203(4) may then be transmitted, via conductors 101 -104 and conductive shield 105, to the RX device 220. As a result of the pre-coding, the EM data 204(1 )-204(4) recovered by the receiver 222 may be substantially similar, if not identical, to the original EM data 202(1 )-202(4) prior to pre-coding. The received EM data 204(1 )-204(4) may further be provided to the MIMO decoder 224, which then decodes the received data streams (e.g., by converting them into their original form). For example, the MIMO decoder 224 may convert the four streams of EM data 204(1 )-204(4) to two streams of output data 205(1 ) and 205(2) (e.g., as a reconstruction of the original input data streams 201 (1 ) and 201 (2)).

[0046] Note that, in some embodiments, transmitter 216 and receiver 222 may be substituted for transceivers that are configured to both transmit and receive data signals over the conductors 101 -104 and/or conductive shield 105. Such a configuration may allow for bidirectional communications between the TX device 210 and the RX device 220. Furthermore, the system 200 described above may be implemented by replacing and/or adding additional circuitry to the front end of existing legacy twisted-pair (e.g., Cat 5 and/or Cat 6) cable applications. Accordingly, the system 200 may provide a low-cost alternative for increasing the data rate of existing twisted pair-based communication systems.

[0047] FIG. 5 is a block diagram illustrating an embodiment of a MIMO data transmission system 500 employing multiple twisted pairs. The system 500 includes a TX device 510 including a number of transmitters 512, 514, and 516 coupled to one end of twisted pairs 150 and 160, and an RX device 520 including a number of receivers 522, 524, and 526 coupled to the other end of the twisted pairs 150 and 160. Specifically, the first transmitter 512 and the first receiver 522 are coupled to conductors 101 and 102, the second transmitter 514 and the second receiver 524 are coupled to conductors 101 and 103, and the third transmitter 516 and the third receiver 526 are coupled to conductors 101 and 104. For some embodiments, an additional (e.g., fourth) transmitter- receiver pair may be coupled to the system 500 to transmit an additional data signal via a conductive shield (not shown for simplicity) of the twisted pairs 150 and 160.

[0048] In operation, the transmitters 512, 514, and 516 receive data streams Data_1 , Data_2, and Data_3, respectively, and output data signals representing the received data streams via the conductors 101 -104. For example, the data streams Data_1 , Data_2, and Data_3 may correspond to EM data streams encoded by a MIMO encoder (e.g., MIMO encoder 212 of FIG. 2) and/or pre-coded by a MIMO pre-coder (e.g., MIMO pre-coder 214 of FIG. 2). For some embodiments, each of the transmitters 512, 514, and 516 may correspond to a transformer (e.g., balun transformer) that is capable of converting the received data stream into a set of pulse-based (e.g., baseband) signal waveforms for transmission over a twisted pair cable. For example, the first transmitter 512 may transmit the data stream Data_1 via the conductors 101 and 102; the second transmitter 514 may transmit the data stream Data_2 via the conductors 101 and 103; and the third transmitter 516 may transmit the data stream Data_3 via the conductors 101 and 104.

[0049] For other embodiments, the transmitters 512, 514, and 516 may correspond to discrete multi-tone (DMT) transmitters capable of converting the received data stream into a set of orthogonal signal waveforms that may be transmitted on multiple carrier (e.g., sub-carrier) frequencies. DMT waveforms may be modulated over a wide and frequency selective bandwidth, for example, by providing a clean channel for each component tone. For some embodiments, bit loading may be achieved (e.g., over different sub-bands) by implementing a different modulation scheme for each tone. For example, the first transmitter 512 may transmit the data stream Data_1 as a sequence of tones modulated with a first modulation scheme; the second transmitter 512 may transmit the data stream Data_2 as a sequence of tones modulated with a second

modulation scheme; and the third transmitter 516 may transmit the data stream Data_3 as a sequence of tones modulated with a third modulation scheme.

[0050] The receivers 522, 524, and 526 may be configured to recover the data streams Data_1 , Data_2, and Data_3, respectively, by decoding the data signals carried by the conductors 101 -104. For some embodiments, each of the receivers 522, 524, and 526 may correspond to a transformer that is capable of converting a sequence of pulse-based data signals to a corresponding data stream. For example, the first receiver 522 may recover the data stream Data_1 from the conductors 101 and 102; the second receiver 524 may recover the data stream Data_2 from the conductors 101 and 103; and the third receiver 526 may recover the data stream Data_3 from the conductors 101 and 104.

[0051 ] For other embodiments, the receivers 522, 524, and 526 may correspond to DMT receivers capable of converting DMT-modulated waveforms to their respective data streams. For example, the first receiver 522 may recover the data stream Data_1 from a received sequence of tones modulated according to a first modulation scheme; the second receiver 524 may recover the data stream Data_2 from a received sequence of tones modulated according to a second modulation scheme; and the third receiver 526 may recover the data stream Data_3 from a received sequence of tones modulated according to a third modulation scheme. It should be noted that the

implementation of a DMT receiver may be much simpler than that of a conventional (e.g., baseband) receiver. Furthermore, DMT signaling may be particularly well-suited for transmitting MIMO-encoded data via a plurality of conductors, as described herein.

[0052] Embodiments herein recognize that backwards compatibility with legacy communications devices is often desirable, especially where one device has no prior knowledge of the communications capabilities of the other devices in a system. Thus, for some embodiments, the transmitters 512-516 and/or receivers 522-526 may be configured to process both pulse-based and DMT- modulated data signals.

[0053] FIG. 6 is a block diagram illustrating another embodiment of a MIMO data transmission system 600 employing multiple twisted pairs. More specifically, the system 600 includes a TX device 610 and an RX device 620, and represents an alternative configuration for the system 500 described above, with respect to FIG. 5. For example, each of the transmitters 512, 514, and 516 of FIG. 5 may be substituted with a corresponding transmitter pair 612A-612B, 614A-614B, and 616A-616B, respectively. Further, each of the receivers 522, 524, and 526 may be substituted with a corresponding receiver pair 622A-622B, 624A-624B, and 626A-626B, respectively. More specifically, transmitter pair 612A-612B is coupled to receiver pair 622A-622B via conductors 101 and 102; transmitter pair 614A-614B is coupled to receiver pair 624A-624B via

conductors 101 and 103; and transmitter pair 616A-616B is coupled to receiver pair 626A-626B via conductors 101 and 104. For some embodiments, an additional transmitter pair and receiver pair may be coupled to the system 600 to transmit an additional data signal via a conductive shield (not shown for simplicity) of the twisted pairs 150 and 160.

[0054] The first transmitter of each transmitter pair (e.g., TX 612A, 614A, and 616A) may convert a received data stream to a set of pulse-based (e.g., baseband) signals. The second transmitter of each transmitter pair (e.g., DTX 612B, 614B, and 616B) may convert the received data stream to a set of DMT- modulated (e.g., sub-carrier) signals. Similarly, the first receiver of each receiver pair (e.g., RX 622A, 624A, and 626A) may recover a transmitted data stream from a received sequence of pulse-based data signals. Further, the second receiver of each receiver pair (e.g., DRX 622B, 624B, and 626B) may recover the transmitted data stream from a received sequence of DMT-modulated signals.

[0055] The data streams Data_1 , Data_2, and Data_3 may be

transmitted by one of the transmitters (TX or DTX) of each transmitter pair, and subsequently recovered by one of the receivers (RX or DRX) of each receiver pair. Selecting which transmitter (TX or DTX) and receiver (RX or DRX) to use may depend on the communications capabilities of the transmitting device and the receiving device. For example, it may be preferable to transmit the data streams as DMT-modulated signals (e.g., using DTX 612B, 614B, and 616B) if the receiving device is capable of processing such DMT signals. Otherwise, if the receiving device is a legacy communications device, it may be desirable to selectively transmit the data streams as conventional pulse-based signals (e.g., using TX 612A, 614A, and 616A).

[0056] Still further, in some embodiments, the data streams Data_1 , Data_2, and Data_3 may be transmitted as a combination of pulse-based and DMT-modulated signals, for example, using both transmitters TX and DTX of each transmitter pair and both receivers RX and DRX of each receiver pair. For example, TX 612A, 614A, and 614B may be used to transmit signals in the baseband (e.g., DC) frequency range while DTX 612B, 614B, and 616B may be used to transmit signals at higher frequency ranges (e.g., based on a carrier frequency). The transmit power of each waveform may be determined during the negotiation phase. Aggregating baseband and DMT waveforms in this manner may help ensure compatibility with legacy devices while also providing improved signal quality to DMT-capable capable devices.

[0057] For some embodiments, a configuration module 619 in the transmitting device 610 may determine the communications capabilities of the receiving device 620 during an initial setup or negotiation phase. The

configuration module 619 may then selectively enable (and/or disable) one or both of the transmitters (TX or DTX) in each transmitter pair, for example, using a selection signal (T_sel).

[0058] FIG. 7 is a block diagram of a communications device 700 that is configurable to communicate with legacy devices in accordance with some embodiments. The communications device 700 includes a MIMO encoder 710, a MIMO pre-coder 720, a communications interface 730, and a configuration module 740. The communications interface 730 includes a baseband

transceiver 732 and a DMT transceiver 734, both of which may be coupled to a set of twisted pairs 706. With reference to FIG. 6, the baseband transceiver 732 may perform the functions of the first transmitter of each transmitter pair (e.g., TX 612A, 614A, and 616A), in addition to the functions of the first receiver of each receiver pair (e.g., RX 622A, 624A, and 626A). For example, the baseband transceiver 732 may transmit and/or receive pulse-based (e.g., baseband) data signals via the twisted pairs 706. The DMT transceiver 734 may perform the functions of the second transmitter of each transmitter pair (e.g., DTX 612B, 614B, and 616B), in addition to the functions of the second receiver of each receiver pair (e.g., DRX 622B, 624B, and 626B). For example, the DMT transceiver 734 may transmit and/or receive DMT-modulated (e.g., sub-carrier) data signals via the twisted pairs 706.

[0059] The MIMO encoder 710, which may be one embodiment of MIMO encoder 212 of FIG. 2, may encode a set of received input data 701 into multiple streams of EM data to be transmitted, concurrently, via the twisted pairs 706. For example, the input data 701 may include a number N of data streams that are intended to be transmitted (e.g., using differential signaling) via a number N of twisted pairs 706, respectively. As described above, with respect to FIGS. 2 and 4, the MIMO encoder 710 may further encode the N data streams into a number M of EM data streams (e.g., M < 2N). For some embodiments, the MIMO encoder 710 may encode the N data streams into 2N EM data streams (e.g., where a conductive shield for the twisted pairs 706 is used to transmit data). For other embodiments, the MIMO encoder 710 may encode the N data streams into 2N-1 EM data streams (e.g., where the conductive shield is not present or unused).

[0060] The MIMO pre-coder 720, which may be one embodiment of

MIMO pre-coder 214 of FIG. 2, may pre-code the EM data to reduce and/or counter the effects of cross-talk and other sources of interference attributable to the twisted pairs 706. As described above, with respect to FIGS. 2 and 4, the MIMO pre-coder 720 may generate a pre-coding matrix based on a channel estimation (H) obtained from the receiving device. For some embodiments, the pre-coding matrix may be the inverse of the channel estimation matrix (e.g., H^"1). It should be noted that the amount of cross-talk between conductors may vary depending on the signal waveforms used to transmit data over the twisted pairs 706. For example, DMT signals may exhibit greater cross-talk than conventional pulse-based signals. Thus, for some embodiments, the MIMO pre-coder 720 may receive a separate channel estimation (e.g. H') associated with DMT signaling (e.g., assuming the receiving device is capable of receiving and/or transmitting DMT signals).

[0061 ] The configuration module 740 may receive configuration

information 702 from another communications device in the system (e.g., coupled to the other ends of the twisted pairs 706) and determine the

configuration capabilities of the other device based on the received information. The configuration module 740 may then selectively enable the MIMO encoder 710 and/or the MIMO pre-coder 720 based on the capabilities of the other device. For example, the configuration module 740 may output a MIMO enable (M_en) signal 703 to the MIMO encoder 710 if the other device is capable of receiving (and/or transmitting) EM data signals. Furthermore, the configuration module 740 may output a pre-coding enable (P_en) signal 704 to the MIMO pre-coder 720 if the channel estimation indicates a relatively high level of crosstalk or interference (e.g., compared to a threshold level). If the MIMO encoder 710 and/or the MIMO pre-coder 720 are not activated, the input data 701 may be passed through (un-encoded) to the communications interface 730.

[0062] The configuration module 740 may further output a transceiver selection (T_sel) signal 705 to the communications interface 730 to activate or enable one or both of the transceivers 732 and/or 734. For example, the configuration module 740 may select either the baseband transceiver 732 or the DMT transceiver 734 to transmit and/or receive data depending on whether the other device is capable of processing DMT-modulated data signals.

Alternatively, the configuration module 740 may activate both the baseband and DMT transceivers 732 and 734 to transmit and/or receive data using

aggregated baseband and DMT waveforms.

[0063] For some embodiments, the configuration module 740 may configure one or more additional communications parameters such as, for example, chip rate and/or data rate. The chip rate may correspond to an overall operating speed of the communications device 700. For example, having a slower chip rate may conserve processing power in both the transmitting device and the receiving device when the achievable data rate is low. Thus, for some embodiments, the configuration module 740 may enable the device 700 to operate at a slower chip rate for longer-distance communications. The data rate may correspond to the frequency at which data signals are output onto the twisted pairs 706. To prevent data loss, the configuration module 740 may ensure that the data rate of the communications device 700 does not exceed the maximum allowable data rate of a communications device at the other end of the twisted pairs 706 (e.g., the frequency with which the receiving device is able to sample or decode received data signals).

[0064] FIG. 8 is an illustrative flow chart depicting an operation 800 for determining a set of communications parameters in accordance with some embodiments. With reference, for example, to FIG 7, the communications device 700 may first generate a set of MIMO-encoded test data to be

transmitted, via the set of twisted pairs 706, to a receiving device (810). The test data may correspond to a predetermined set of data known to both the communications device 700 and the receiving device. For example, the test data may be initially provided as N data streams to the MIMO encoder 710, which then converts the N data streams to M streams of EM test data (e.g., M < 2N) to be transmitted via the 2N conductors that form N twisted pairs 706.

[0065] The communications device 700 may transmit the test data using both baseband (e.g., legacy) and DMT signaling techniques (820). For some embodiments, a set of DMT signals may be appended to a set of baseband signals. For example, the baseband transceiver 732 may first transmit the EM test signals as a first set of test signals using conventional pulse-based (e.g., baseband) signaling techniques (e.g., as described above with respect to FIGS. 5 and 6). Next, the DMT transceiver 734 may immediately retransmit the EM test signals as a second set of test signals using DMT-modulation techniques (e.g., as described above with respect to FIGS. 5 and 6). Accordingly, a receiving device may acknowledge the second set of test signals if (and only if) it is capable of processing DMT signals.

[0066] The communications device 700 then receives a response from the other device (830) and determines a number of communication parameters based on the response (840). For example, the communications device 700 may receive the response via one or more of the transceivers 732 and/or 734. For some embodiments, the configuration module 740 may first determine whether the receiving device is capable of processing DMT signals. For example, the configuration module 740 may receive an acknowledgement or confirmation of receipt of the DMT signals and/or a corresponding channel estimation (Η') from the receiving device. For some embodiments, the configuration module 740 may determine that the receiving device is capable of processing DMT signals if it receives two successive acknowledgements and/or channel estimations from the receiving device (e.g., one for each transmission).

[0067] If the receiving device is capable of DMT-based communications, the configuration module 740 may activate the MIMO encoder 710 and select the DMT transceiver 734 to transmit and/or receive data signals via the twisted pairs 706. The configuration module 740 may then determine whether MIMO pre-coding should be enabled. For example, the configuration module 740 may determine whether to activate the MIMO pre-coder 720 based on the channel estimation (Η') received from the receiving device. For some embodiments, MIMO pre-coding may be enabled if the channel estimation (Η') indicates that cross-talk or interference in the channel is above a threshold level (e.g., thus causing one or more data symbols to be received incorrectly). On the other hand, MIMO pre-coding may be unnecessary if the channel is relatively stable or reliable. If MIMO pre-coding is enabled, the configuration module 740 may further provide the channel estimation (Η') to the MIMO pre-coder 720. The MIMO pre-coder 720 may then generate a pre-coding matrix, based on the channel estimation (Η'), to be applied to the outgoing EM data streams. More specifically, the pre-coding parameters may be applied with respect to each sub-band of the DMT signals.

[0068] For some embodiments, the communications device 700 may further determine one or more encoding parameters for the transmitted DMT signals such as, for example, cyclic prefix length, sub-carrier spacing, and/or sub-band size. For some embodiments, the cyclic prefix length may be determined by the DMT transceiver 734. For example, a longer cyclic prefix may be used for longer distance communications. The sub-band size may also be adjusted depending on the distance of communications. For example, the configuration module 740 may implement a narrow sub-band for longer distance communications. For some embodiments, the configuration module 740 may adjust the sub-carrier spacing by varying the chip rate. For example, the configuration module 740 may fix the FFT size when the chip rate changes.

[0069] If the receiving device is incapable of processing DMT signals (or if no confirmation was received in response to the DMT-based test signals), the configuration module 740 may select the baseband transceiver 732 to transmit and/or receive data signals via the twisted pairs 706. The configuration module 740 may then determine whether to enable MIMO encoding. For example, the configuration module 740 may determine that the receiving device is capable of processing MIMO-encoded data signals if it receives an acknowledgement or confirmation of receipt of the EM test signals and/or a corresponding channel estimation (H) from the receiving device. If the receiving device is unable to decode the EM test signals (e.g., based on their known values), it may subsequently request retransmission of the test signals by the communications device 700. For some embodiments, the receiving device may respond to the EM test signals by transmitting its own set of EM test signals to the

communications device 700. Accordingly, the communications device 700 may determine that the receiving device is capable of processing MIMO-encoded data signals upon receiving such EM test signals from the receiving device.

[0070] If the receiving device is capable of processing EM data signals, the communications device 700 may then determine whether MIMO pre-coding should be enabled. For example, the configuration module 740 may determine whether to active the MIMO pre-coder 720 based on the channel estimation (H) received from the receiving device. For some embodiments, MIMO pre-coding may be enabled if the channel estimation (H) indicates that cross-talk or interference in the channel is above a threshold level (e.g., thus causing one or signal pulses to be received incorrectly). On the other hand, pre-coding may be unnecessary if the channel is relatively stable or reliable. If pre-coding is enabled, the configuration module 740 may further provide the channel estimation (H) to the MIMO pre-coder 720. The MIMO pre-coder 720 may then generate a pre-coding matrix, based on the channel estimation (H), to be applied to the outgoing EM data streams. More specifically, the pre-coding parameters may be applied with respect to the signals transmitted via each individual conductor of the multiple twisted pairs 706.

[0071 ] If the receiving device is a legacy device that is incapable of processing EM data signals and/or DMT waveforms, the configuration module 740 may disable both the MIMO encoder 710 and the MIMO pre-coder 720. The configuration module 740 may further select the baseband transceiver 732 to handle the transmission and/or reception of data signals via the twisted pairs 706. This allows the input data 701 to pass straight through (un-encoded) to the baseband transceiver 732.

[0072] FIG. 9 is a block diagram of a communications device 900 in accordance with some embodiments. The device 900 includes a cable interface 910, a platform interface 920, a processor 930, and a memory 940. The cable interface 910 is coupled to the processor 930 and may be used to transmit and/or receive data signals over a data cable (e.g., including multiple twisted pairs with or without a conductive shield) in a manner prescribed by the processor 930. For example, the cable interface 910 may be configured to transmit and/or receive data signals using pulse-based (e.g., baseband) signaling techniques. Alternatively, or in addition, the cable interface 910 may be configured to transmit and/or receive data signals using DMT-modulation techniques. The platform interface 920 is also coupled to the processor 930, and may be used to communicate data to and/or from a computing platform (e.g., via a PCIe link).

[0073] Memory 940 may include a data store 942 that may be used to temporarily buffer data to be encoded and/or decoded. For some embodiments, the data store 942 may further store a set of predetermined test data to be used for purposes of configuring one or more communications parameters of the device 900. Furthermore, memory 940 may also include a non-transitory computer-readable storage medium (e.g., one or more nonvolatile memory elements, such as EPROM, EEPROM, Flash memory, a hard drive, etc.) that can store the following software modules:

• a MIMO encoding module 944 to encode outgoing data for MIMO-based transmission over a data cable;

• a MIMO pre-coding module 946 to pre-code EM data signals to counter and/or suppress the effects of cross-talk and other interference along the communications channel; and

• a configuration module 948 to selectively enable one or more data

communication features of the device 900.

Each software module may include instructions that, when executed by the processor 930, may cause the device 900 to perform the corresponding function. Thus, the non-transitory computer-readable storage medium of memory 940 may include instructions for performing all or a portion of the operations described with respect to FIGS. 3, 4, and 8.

[0074] The processor 930, which is coupled to the memory 940, may be any suitable processor capable of executing scripts of instructions of one or more software programs stored in the communications device 900 (e.g., within memory 940). For example, the processor 930 may execute the MIMO encoding module 944, the MIMO pre-coding module 946, and/or the

configuration module 948.

[0075] The MIMO encoding module 944 may be executed by the processor 930 to encode data signals to be transmitted over the data cable. For example, the MIMO encoding module 944, as executed by the processor 930, may receive a set of data (e.g., from the computing platform) to be transmitted via the data cable, and may encode the data set to produce multiple subsets of data. For some embodiments, the processor 930, in executing the MIMO encoding module 944, may partition the received data set to be transmitted over the data cable as a plurality of separate and/or parallel sets of EM data signals. The processor 930, in executing the MIMO encoding module 944, may then cause the EM data signals to be transmitted via the data cable such that at least one conductive element of the data cable is used in the transmission of two or more of data signals, concurrently (e.g., as described above with respect to FIGS. 1A and 1 B).

[0076] The MIMO pre-coding module 946 may be executed by the processor 930 to pre-code EM data signals to counter and/or suppress the effects of cross-talk and other interference along the communications channel. For example, the MIMO pre-coding module 946, as executed by the processor 930, may generate a pre-coding matrix (e.g., based on a received channel estimation) to be applied to the EM data signals prior to transmission. For some embodiments, the processor 930, in executing the MIMO pre-coding module 946, may determine the pre-coding parameters based on an amount of interference attributable to each pair of conductors of the data cable and/or sub- band of a DMT sub-carrier signal.

[0077] The configuration module 948 may be executed by the processor 930 to selectively enable one or more data communication features of the device 900. For some embodiments, the configuration module 948 may be executed by the processor 930 during an initial setup or negotiation phase to determine the communications capabilities of another device coupled to the data cable (e.g., a receiving device). For example, as described above with respect to FIGS. 7 and 8, the configuration module 948, as executed by the processor 930, may determine chip and data rates for the device 900, whether to enable MIMO encoding (e.g., based on whether the other device is able to process EM data signals), whether to enable MIMO pre-coding (e.g., based on the channel estimation), and/or whether the data signals are to be transmitted using baseband and/or DMT signaling techniques (e.g., based on whether the other device is able to process DMT signals). Thus, in executing the

configuration module 948, the processor 930 may further determine whether to execute the MIMO encoding module 944 and/or the MIMO pre-coding module 946.

[0078] The various signal transmission techniques described herein with respect to the exemplary embodiments may provide higher data rates across multiple twisted pairs than conventional data transmission techniques. In addition, at least some of the present embodiments may mitigate cross-talk and/or other interference among twisted pairs to ensure that data is reliably and accurately transmitted across a communications channel. Using DMT

modulation techniques may further allow for simpler receiver design.

Furthermore, the present embodiments may be implemented in legacy data communications systems with little modification to the existing hardware infrastructure.

[0079] In the foregoing specification, the present embodiments have been described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader scope of the disclosure as set forth in the appended claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense. For example, the method steps depicted in the flow charts of FIGS. 3, 4 and 8 may be performed in other suitable orders, multiple steps may be combined into a single step, and/or some steps may be omitted.

Claims

CLAIMS What is claimed is:

1 . A method of transmitting signals over a plurality of twisted pairs, the method comprising:

determining a channel estimation based, at least in part, on interference attributable to a number 2N of conductors that form N twisted pairs, wherein N is an integer greater than or equal to 2; and

pre-coding at least 2N-1 data streams, based on the channel estimation, to be concurrently transmitted over the N twisted pairs.

2. The method of claim 1 , wherein determining the channel estimation comprises:

transmitting a set of test signals, via the N twisted pairs, from a first device to a second device; and

receiving the channel estimation, based on the set of test signals, from the second device.

3. The method of claim 2, wherein transmitting the set of test signals comprises:

transmitting 2N-1 test signals, concurrently, over the N twisted pairs, wherein each of the 2N-1 test signals is transmitted on a separate one of a group of 2N-1 of the conductors, and wherein another of the conductors comprises a common return path.

4. The method of claim 2, wherein transmitting the set of test signals comprises:

transmitting 2N test signals, concurrently, over the N twisted pairs, wherein each of the 2N test signals is transmitted on a separate one of the 2N conductors, and wherein a conductive shield for the N twisted pairs comprises a common return path.

5. The method of claim 1 , wherein pre-coding the at least 2N-1 data streams comprises:

generating a pre-coding matrix based on the channel estimation; and applying the pre-coding matrix to each of the 2N-1 data streams to be transmitted.

6. The method of claim 1 , wherein pre-coding the at least 2N-1 data streams comprises:

pre-coding 2N data streams to be transmitted, concurrently, over the N twisted pairs, wherein each of the 2N data streams is to be transmitted on a separate one of the 2N conductors, and wherein a conductive shield for the N twisted pairs comprises a common return path.

7. The method of claim 1 , further comprising:

transmitting the pre-coded data streams as discrete multi-tone (DMT) signals.

8. A method of transmitting signals over a plurality of twisted pairs, the method comprising:

transmitting a set of negotiation data, via a number N of twisted pairs, to a receiving device, wherein N is an integer greater than or equal to 2;

receiving a response from the receiving device; and

determining a number of data signals to be concurrently transmitted over the number of N twisted pairs based, at least in part, on the response from the receiving device.

9. The method of claim 8, wherein transmitting the set of negotiation data comprises:

transmitting at least 2N-1 test signals, concurrently, over the number of N twisted pairs.

10. The method of claim 9, further comprising:

transmitting N data signals are to be transmitted, concurrently, over the number of N twisted pairs when the response does not include a confirmation of receipt of the at least 2N-1 test signals.

1 1 . The method of claim 9, further comprising:

transmitting at least 2N-1 data signals, concurrently, over the number of N twisted pairs when the response includes a confirmation of receipt of the at least 2N-1 test signals.

12. The method of claim 1 1 , wherein the response includes a channel estimation based, at least in part, on interference attributable to 2N conductors that form the N twisted pairs.

13. The method of claim 12, further comprising:

determining whether to pre-code the 2N-1 data signals based on the channel estimation.

14. The method of claim 8, wherein transmitting the set of negotiation data comprises:

transmitting the set of negotiation data using discrete multi-tone (DMT) modulation techniques.

15. The method of claim 14, further comprising:

determining whether to transmit the data signals using DMT modulation techniques based on the response from the receiving device.

16. A system for transmitting signals over a plurality of twisted pairs, the system comprising:

means for determining a channel estimation based, at least in part, on interference attributable to a number 2N of conductors that form N twisted pairs, wherein N is an integer greater than or equal to 2; and

means for pre-coding at least 2N-1 data streams, based on the channel estimation, to be concurrently transmitted over the N twisted pairs.

17. The system of claim 16, wherein the means for determining the channel estimation comprises:

means for transmitting a set of test signals, via the N twisted pairs, from a first device to a second device; and

means for receiving the channel estimation, based on the set of test signals, from the second device.

18. The system of claim 17, wherein the means for transmitting the set of test signals comprises:

means for transmitting 2N-1 test signals, concurrently, over the N twisted pairs, wherein each of the 2N-1 test signals is transmitted on a separate one of a group of 2N-1 of the conductors, and wherein another of the conductors comprises a common return path.

19. The system of claim 17, wherein the means for transmitting the set of test signals comprises:

means for transmitting 2N test signals, concurrently, over the N twisted pairs, wherein each of the 2N test signals is transmitted on a separate one of the 2N conductors, and wherein a conductive shield for the N twisted pairs comprises a common return path.

20. The system of claim 16, wherein the means for pre-coding the at least 2N-1 data streams comprises:

means for generating a pre-coding matrix based on the channel estimation; and

means for applying the pre-coding matrix to each of the 2N-1 data streams to be transmitted.

21 . The system of claim 16, wherein the means for pre-coding at least 2N-1 data streams comprises:

means for pre-coding 2N data streams to be transmitted, concurrently, over the N twisted pairs, wherein each of the 2N data streams is to be

transmitted on a separate one of the 2N conductors, and wherein a conductive shield for the N twisted pairs comprises a common return path.

22. The system of claim 16, further comprising:

means for transmitting the pre-coded data streams as discrete multi-tone (DMT) signals.

23. A device for transmitting signals over a plurality of twisted pairs, the device comprising:

means for transmitting a set of negotiation data, via a number N of twisted pairs, to a receiving device, wherein N is an integer greater than or equal to 2;

means for receiving a response from the receiving device; and

means for determining a number of data signals to be concurrently transmitted over the number of N twisted pairs based, at least in part, on the response from the receiving device.

24. The device of claim 23, wherein the means for transmitting the set of negotiation data comprises:

means for transmitting at least 2N-1 test signals, concurrently, over the number of N twisted pairs.

25. The device of claim 24, further comprising:

means for transmitting N data signals are to be transmitted, concurrently, over the number of N twisted pairs when the response does not include a confirmation of receipt of the at least 2N-1 test signals.

26. The device of claim 24, further comprising:

means for transmitting at least 2N-1 data signals, concurrently, over the number of N twisted pairs when the response includes a confirmation of receipt of the at least 2N-1 test signals.

27. The device of claim 26, wherein the response includes a channel estimation based, at least in part, on interference attributable to 2N conductors that form the number of N twisted pairs.

28. The device of claim 27, further comprising:

means for determining whether to pre-code the 2N-1 data signals based on the channel estimation.

29. The device of claim 23, wherein the means for transmitting the set of negotiation data comprises:

means for transmitting the set of negotiation data using discrete multi- tone (DMT) modulation techniques.

30. The device of claim 29, further comprising:

means for determining whether to transmit the data signals using DMT modulation techniques based on the response from the receiving device.