WO2012045448A1

WO2012045448A1 - Dynamic pilot placement

Info

Publication number: WO2012045448A1
Application number: PCT/EP2011/004965
Authority: WO
Inventors: Vladimir Oksman; Joon Bae Kim
Original assignee: Lantiq Deutschland Gmbh
Priority date: 2010-10-07
Filing date: 2011-10-05
Publication date: 2012-04-12

Abstract

Implementations related to dynamic pilot placement are described. In one implementation, a data frame is generated and includes one or more pilot tone sequences that may be selected by a receiver of the data frame. A subsequent data frame may be generated with a pilot tone sequence selected by the receiver of the data frame.

Description

DYNAMIC PILOT PLACEMENT

[0001] Data packet transmission in multipoint-to-multipoint networks (e.g., ad- hoc or mesh networks) is usually arranged by sending one or more data packets. A data packet is often encoded and modulated. Also, a data packet typically includes at least one frame. Each frame may include a preamble. The primary purposes of the preamble include 1 ) enabling the receiver of the frame to detect the frame on the transmission medium, 2) adjusting the gain of the receiver (e.g., an analog front end (AFE)) and synchronizing the clock so that frame is received when expected. The frame also has a header that carries information helping the receiver to address, demodulate, and decode the frame. Furthermore, the frame may include payload that carries data. Pilot tones may be added to the preamble, header and payload in order to enable timing recovery or channel adaptation at the receiver.

[0002] Because of their ubiquitous nature, powerlines are increasing in popularity as a transmission medium for many networks. Unfortunately, powerlines are a notoriously noisy medium for data communications. Noise disturbs all parts of the data packet, including pilot tones located in various locations of the data packet. Other transmission medium and the noise associated therewith may also disturb pilot tones located at various locations of the data packet.

[0003] The independent claims define the invention in various aspects. The dependent claims define embodiments of the invention.

[0004] In a first aspect, the invention encompasses a method that may include generating a first communication that includes information related to one or more pilot tone sequences; transmitting the first communication on a communication medium; and receiving a second communication that includes a request to switch to one of the one or more pilot tone sequences. At least one effect of the foregoing method is that a multicarrier apparatus may request pilot tone reallocation based on an analysis of channel parameters and a single communication to a transmitting multicarrier apparatus.

[0005] In an embodiment of the method according to the invention in the first aspect the first communication of the generating act is a frame including a preamble, a header and a payload, the information related to one or more pilot tone sequences contained in the header. In an embodiment, the payload may be zero.

[0006] In an embodiment of the method according to the invention in the first aspect the information is a nonzero integer value indicating a number of tones each pilot tone in at least the payload is to shift from a current position.

[0007] In an embodiment of the method according to the invention in the first aspect the second communication is an acknowledgement frame from a receiver of the first communication, and the request is represented in one or more bit values associated with the acknowledgement frame.

[0008] In an embodiment of the method according to the invention in the first aspect the second communication is a Bit Allocation Table (BAT) from a receiver of the first communication, the BAT including at least information related to a pilot tone sequence that is different than a pilot tone sequence associated with the first communication. [0009] In an embodiment of the method according to the invention in the first aspect the information is a plurality of payload pilot tone sequences that may be selected by a receiver of the first communication.

[0010] In an embodiment of the method according to the invention in the first aspect the information is a plurality of frame pilot tone sequences that may be selected by a receiver of the first communication.

[0011] In a second aspect the invention encompasses an apparatus, which may include a transceiver configured to: generate a first communication that includes information related to one or more pilot tone sequences; transmit the first communication on a communication medium; and receive a second communication that includes a request to switch to one of the one or more pilot tone sequences. At least one effect of the foregoing apparatus is that a multicarrier apparatus may request pilot tone reallocation based on an analysis of channel parameters and a single communication to a transmitting multicarrier apparatus.

[0012] In an embodiment of the apparatus according to the invention in the second aspect the first communication is a frame including a preamble, a header and a payload, the information related to one or more pilot tone sequences contained in the header.

[0013] In an embodiment of the apparatus according to the invention in the second aspect the second communication is an acknowledgement frame from a receiver of the first communication, and the request is represented in one or more bit values associated with the acknowledgement frame. [0014] In an embodiment of the apparatus according to the invention in the second aspect the second communication is a Bit Allocation Table (BAT) from a receiver of the first communication, the BAT including at least information related to a pilot tone sequence that is different than a pilot tone sequence associated with the first communication.

[0015] In an embodiment of the apparatus according to the invention in the second aspect the information is a plurality of payload pilot tone sequences that may be selected by a receiver of the first communication.

[0016] In an embodiment of the apparatus according to the invention in the second aspect the information is a plurality of frame pilot tone sequences that may be selected by a receiver of the first communication.

[0017] Below, a detailed description is described with reference to the accompanying figures.

[0018] FIG. 1 illustrates an exemplary communication arrangement that employs at least two multicarrier apparatuses. In one implementation, the multicarrier apparatuses are Orthogonal Frequency Division Multiplexing (OFDM) capable apparatuses capable of implementing the described dynamic pilot placement implementations.

[0019] FIG. 2 illustrates an exemplary transceiver apparatus that may be used as a transmitting apparatus and receiving apparatus in a multicarrier arrangement or system. The multicarrier apparatuses illustrated in FIG. 1 may be implemented in the same or similar manner as the exemplary transceiver apparatus. [0020] FIG. 3 is a flow diagram of a procedure useable to enable dynamic pilot tone placement.

[0021] FIG. 4 illustrates exemplary data frame structures.

[0022] In the figures, the left-most digit(s) of a reference number identifies the figure in which the reference number first appears. The use of the same reference number in different instances in the description and the figures may indicate similar or identical items.

Overview

[0023] The following description describes exemplary implementations related to dynamic pilot symbol or tone placement in a communication system. As will be understood from this description, the exemplary implementations described herein may offer numerous advantages over conventional systems that implement pilot symbols or tones that are not capable of being modified or otherwise changed. By way of example, the implementations described herein may enable a receiver to better protect pilots against dynamically changing narrowband interference without increasing number of pilot tones. Furthermore, the exemplary implementations described herein may allow a transmitter to change the location of pilot tones from frame to frame with or without feedback from the receiver.

Exemplary Communication Arrangement

[0024] FIG. 1 illustrates an exemplary communication arrangement 100 that employs at least two multicarrier apparatuses 102 and 104. In one implementation, the multicarrier apparatuses 102 and 104 are Orthogonal Frequency Division Multiplexing (OFDM) capable apparatuses capable of implementing the herein described dynamic pilot placement procedures.

[0025] The multicarrier apparatuses 102 and 104 may communicate through a bidirectional communication channel 106. The communication channel 106 may be realized as a wireless medium or a wireline medium. Accordingly, the multicarrier apparatuses 102 and 104 may include structure and functionality that enables signal communication over such medium. Such structure and functionality may include one or more antennas, integrated wireline interfaces, and the like.

[0026] Furthermore, the multicarrier apparatuses 102 and 104 may be enabled to communicate using packet-based technology (e.g., ITU G.hn, HomePNA, HomePlug® AV and Multimedia over Coax Alliance (MoCA)) and xDSL technology. Such xDSL technology may include Asymmetric Digital Subscriber Line (ADSL), ADSL2, ADSL2+, Very high speed DSL (VDSL), VDSL2, G.Lite, and High bit rate Digital Subscriber Line (HDSL), as well as other packet based technologies such as xPON (Passive Optical Networks). In addition, the multicarrier apparatuses 102 and 104 may be enabled to communicate using IEEE 802.11 and IEEE 802.16 (WiMAX) wireless technologies.

[0027] Signals exchanged between the multicarrier apparatuses 102 and 104 may include multicarrier symbols that each include a plurality of tones, also known as sub-channels. Each of the tones within a multicarrier symbol may have data bits modulated thereon that are intended for delivery from one of the multicarrier apparatuses 102 and 104 to the other. [0028] FIG. 2 illustrates an exemplary transceiver apparatus 200 that may be used as a transmitting apparatus or receiving apparatus in a multicarrier arrangement or system. The multicarrier apparatuses 102 and 104 illustrated in FIG. 1 may be implemented in the same or similar manner as the exemplary transceiver apparatus 200. To simplify the description of the implementations described herein, dynamic pilot placement may be discussed in connection with the apparatus 200.

[0029] The transceiver apparatus 200 may include a transmitter 202 that incorporates a number of different elements. For example, the transmitter 202 may include an encoder 204, a modulator 206, a filter 208, an interface 210 and a controller 212. As used herein, the term "controller" is meant generally to include all types of digital processing devices including, without limitation, digital signal processors (DSPs), reduced instruction set computers (RISC), general-purpose (CISC) processors, microprocessors, gate arrays (e.g., FPGAs), PLDs, reconfigurable compute fabrics (RCFs), array processors, secure microprocessors, and application-specific integrated circuits (ASICs). Such digital processors may be contained on a single unitary IC die, or distributed across multiple components.

[0030] Furthermore, the transmitter 202 may include one or more Bit Allocation Tables (BATs) 214 stored in storage. As used herein, the term "storage" and the like may refer to any type of integrated circuit or other storage device adapted for storing digital data including, without limitation, ROM, PROM, EEPROM, DRAM, SDRAM, DDR/2 SDRAM, EDO/FPMS, RLDRAM, SRAM, "flash" memory (e.g., NAND/NOR), and PSRAM. The encoder 204 may be capable of receiving data that is for communication to a receiving device coupled to the transceiver apparatus 200 via a wireless or wireline medium 216. More specifically, the encoder 204 may be capable of translating incoming data bit streams into in-phase and quadrature components for each of the plurality of tones. The encoder 204 may be arranged to output a number of symbol sequences that are equal to the number of tones available to the system. The modulator 206 may be capable of receiving symbol sequences to produce a modulated signal in the form of a discrete multi-tone signal. The modulator 206 may pass the modulated signal to the filter 208 to undergo various filtering and then the filtered signal may be passed to the interface 210 for communication over the medium 216 to a receiving device.

[0031] The transceiver apparatus 200 may also include a receiver 218 that is capable of receiving modulated multi-tone signals communicated over the medium 216. The receiver 218 may include an interface 220, a filter 222, a demodulator 224, a decoder 226 and a controller 228. Furthermore, the receiver 218 may include one or more BATs 230 stored in storage. Signals received by the receiver 218 may be passed to the filter 222 via the interface 220. After receive signals undergo filtering by way of the filter 222, the filtered signals may be demodulated by the demodulator 224. The demodulated signals may be passed to and processed by the decoder 226. The decoder 226 produces data bit streams for consumption by a computing device, or the like. Effectively, the demodulator 224 and the decoder 226 perform the opposite functions of the modulator 206 and the encoder 204, respectively.

[0032] The receiver 218 may monitor channel performance (e.g., the occurrence of noise) and control and adapt bits and gain allocated to one or more of the tones associated with a channel of the multicarrier system. In particular, the receiver 218, by way of the controller 228, may monitor the tones and the signals carried thereon to determine the necessity of a change in the BATs 230 and 214 associated with the receiver 218 and transmitter 202, respectively. In one implementation, the BATs 214 and 230 may store the number of bits and gain to be used by each tone in the multicarrier system. In another implementation, the receiver 218, by way of the controller 228, may monitor the channel to determine if it may be beneficial to update one or more channel adaptation parameters. Such parameters may include a BAT grouping factor, guard interval, Forward Error Correction (FEC) rate, FEC block size, Power Spectral Density (PSD) ceiling, or the like.

[0033] As described, the receiver 218, by way of the controller 228 or another element associated therewith, may monitor the tones and the signals carried thereon. In one implementation, the controller 228 may determine the noise level, gain and phase shift on each of the tones. The object may be to estimate the Signal-to-Noise Ratio (SNR) for each of the tones. Other parameters could be monitored as well or in place of the parameters described. The determination of which tones to transmit the encoded data over as well as how much data to transmit over each tone may be determined on the basis of several factors. The factors may include detected communication medium or channel quality parameters, tone gain parameter, a permissible power mask, and the desired maximum bit error rates. It is noted that the factors need not be constant between tones and indeed may even vary during use. Most notably, the communication medium or channel quality parameters may be repeatedly checked, and adjustments in the modulation scheme made in real time to adjust the modulation as the communication medium or channel quality over various tones changes during use.

Exemplary Procedures

[0034] Exemplary procedures are described below. It should be understood that certain acts need not be performed in the order described, and may be modified, and/or may be omitted entirely, depending on the circumstances. The acts described may be implemented and executed by a computer, processor or other computer device, such as a wireless or wireline device, based on instructions stored on one or more computer-readable storage media. The computer-readable storage media can be any available media that can be accessed by a computer device to implement the instructions stored thereon. As used herein, the term "instructions", "computer program" or "software" is meant to include any sequence or human or machine cognizable acts which perform a function. The exemplary procedures and acts may be rendered in virtually any programming language or environment including, for example, C/C++, Fortran, COBOL, PASCAL, assembly language, markup languages (e.g., HTML, SGML, XML, VoXML), and the like, as well as object-oriented environments such as the Common Object Request Broker Architecture (CORBA), Java™ (including J2ME, Java Beans, etc.), Binary Runtime Environment (BREW), and the like. Furthermore, the disclosed exemplary procedures and associated acts may be hardware and firmware as well, or alternatively as some combination thereof.

[0035] FIG. 3 is a flow diagram of a procedure 300 useable to enable dynamic pilot tone placement. The procedure is compatible with apparatuses, elements and wireless/wireline networks illustrated in FIGS. 1-2, as well as entities and devices other than those illustrated and discussed herein.

[0036] At Act 302, a transmitter of a transceiver generates data, embodied in a frame that may include a preamble, header and payload, for communication on a communication medium. The frame may include a plurality of tones. A first plurality of tones may be associated with the preamble, a second plurality of tones may be associated with the header and a third plurality of tones may be associated with the payload.

[0037] At Act 304, the transmitter may select a number of the total tones as pilot tones. For example, a frame may include 64 tones, the transmitter may select tones 11 , 25, 39 and 53 as pilot tones. In this example, pilot tones are assigned equidistantly, every 14 tones, starting from the first pilot tone position. Generically, pilot tones may be assigned equidistantly, every n-th tone, starting from the first tone, or starting from the first pilot tone location. In one implementation, the tone sequences used in the preamble, header and/or payload may be different. That is, each section (preamble, header and payload) of the frame may implement pilot tone placement using a different n integer value.

[0038] At Act 306, the transmitter generates one or more secondary pilot tone sequences. The secondary pilot tone sequences may be communicated as information in the frame. For example, in one implementation, the transmitter may generate secondary pilot tone sequences that are indicated by one or more integer values n carried in the preamble, header or payload. Integer values n that are greater than an n value representing a current pilot tone sequence in the frame may indicate fewer pilot tones, and integer values n that are less than the n value representing the current pilot tone sequence in the frame may indicate more pilot tones. In another implementation, the transmitter may generate one or more integer values m carried in the preamble, header or payload. The one or more integer values m indicates a shift in tone indices from current pilot tone locations to shifted pilot tone locations. For example, if a frame's pilot tones are located at tones 11 , 25, 39 and 53, m=3 would indicate shifting the pilot tones to 14, 28, 42 and 56. Implementations using both n and m values to provide secondary pilot tone sequences are also contemplated. It may be desirable to increase or decrease the number of pilot tones and also shift pilot tones. In yet another implementation, the one or more secondary pilot tone sequences may include actual tone indices that may be used for pilot tones. For example, a first secondary pilot tone sequence may be identified by a first set with {xi, x₂, X3, X4} tone indices and a second set {yi, y₂, V3}, where x_n and y_n are tone indices for use as pilot tones.

[0039] At Act 308, the transmitter includes the one or more secondary pilot tone sequences in the frame 310. The one or more secondary pilot tone sequences may be carried in any portion of the frame. In one implementation, the secondary pilot tone sequences may be carried in the header. The transmitter transmits the frame 310 to a receiving transceiver.

[0040] At Act 312, the receiving transceiver receives the frame 310, which includes the one or more secondary pilot tone sequences. The receiving transceiver may determine that one of the one or more secondary pilot tone sequences would be advantageous to implement. That is, the receiving transceiver may, as part of monitoring channel performance and channel noise/interference, determine that use of a secondary pilot tone sequence would be beneficial. For example, the receiving transceiver may determine that it would be beneficial to modify the pilot tone placement in each of the parts (e.g., preamble, header and payload) of subsequently received frames. In another example, the receiving transceiver may determine that it would be beneficial to modify the pilot tone placement in the payload only. That is, channel estimation by the receiving transceiver may be improved by way of a frame that uses diverse pilot sequences in the various sections of the frame (e.g., preamble, header and payload).

[0041] At Act 314, the receiving transceiver selects at least one of the one or more secondary pilot tone sequences for use in at least a portion of a subsequent frame transmitted by the transmitting transceiver.

[0042] At Act 316, the receiving transceiver generates a message frame (e.g., acknowledgment message or special management message) that includes the selected one of the one or more secondary pilot tone sequences for use in subsequent communications from the transmitting transceiver and sends the message to the transmitting transmitter.

[0043] At Act 318, the transmitting transmitter receives the message from the receiving transceiver, determines that the message includes a request to modify a current pilot tone sequence, and generate a subsequent frame that uses the requested secondary pilot tone sequence. The request may be communicating in one or more bit values associated with the acknowledgement frame

[0044] In yet another implementation, the receiving transceiver, as a part of channel estimation and adaptive bit loading, may analyze a received frame and indicate to the transmitting transceiver the tones that shall be used as pilot tones in conjunction with a particular BAT conveyed from the receiving transceiver to the transmitting transceiver. That is, the transmitting transceiver receives the BAT and loads bits and pilot tones as requested by the receiving transceiver.

[0045] In yet another implementation, several standard sequences of pilot tones are defined and each associated with a particular BAT. All transceiver apparatuses may have knowledge of the several sequences of pilot tones. When a receiving transceiver processes a received data frame it estimates the error in channel estimation while using the pilot tones in the received data frame. If the error is high, the receiving transceiver sends in a message frame (e.g., an acknowledgement frame) an indication to switch the pilot sequence to one of the standard sequences of pilot tones known to the transceiver apparatus.

[0046] FIG. 4 illustrates exemplary data frame structures 400 and 402. The horizontal index axes of the structures 400 and 402 designate tones. In the data frame structure 400, pilots are located at tones 11 , 25, 39 and 53. The data frame structure 400 may be communicated to a receiving transceiver before the data frame structure 402 is communicated to the receiving transceiver. The frame structure 400 may include one or more alternative sequences of pilot tones that a receiving transceiver may select from. The data frame structure 402 includes pilot tones each shifted by three tones. The data frame structure 402 may be used in response to a request from the receiving transceiver to shift pilot tones by three tones.

[0047] As should be understood from the foregoing, the implementations described herein may offer numerous advantages over conventional pilot tone allocation procedures. By way of example, the implementations described herein may reduce the amount of time required to allocate pilot tones. That is, a receiver may quickly pick from one or more alternative pilot tone sequences as part of normal communications with a transmitter.

[0048] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as preferred forms of implementing the claims. The specific features and acts described in this disclosure and variations of these specific features and acts may be implemented separately or may be combined.

Claims

1. A method, comprising:

generating a first communication that includes information related to one or more pilot tone sequences (302, 306, 308);

transmitting the first communication on a communication medium (308); and receiving a second communication that includes a request to switch to one of the one or more pilot tone sequences (314, 316, 318).

2. The method according to claim 1 , wherein the first communication of the generating act is a frame (310) including a preamble, a header and a payload, the information related to one or more pilot tone sequences contained in the header.

3. The method according to claim 2, wherein the information is a nonzero integer value indicating a number of tones each pilot tone in at least the payload is to shift from a current position.

4. The method according to any of the preceding claims, wherein the second communication is an acknowledgement frame from a receiver of the first communication, and the request is represented in one or more bit values associated with the acknowledgement frame.

5. The method according to any of the preceding claims, wherein the second communication is a Bit Allocation Table (BAT) from a receiver of the first communication, the BAT including at least information related to a pilot tone sequence that is different than a pilot tone sequence associated with the first communication.

6. The method according to any of the preceding claims, wherein the information is a plurality of payload pilot tone sequences that may be selected by a receiver of the first communication.

7. The method according to any of the preceding claims, wherein the information is a plurality of frame pilot tone sequences that may be selected by a receiver of the first communication.

8. An apparatus, comprising:

a transceiver (200) configured to:

generate a first communication that includes information related to one or more pilot tone sequences (302, 306, 308);

transmit (308) the first communication on a communication medium (216); and

receive a second communication that includes a request to switch to one of the one or more pilot tone sequences (314, 316, 318).

9. The apparatus according to claim 8, wherein the first communication is a frame (310) including a preamble, a header and a payload, the information related to one or more pilot tone sequences contained in the header.

10. The apparatus according to claim 9, wherein the information is a nonzero integer value indicating a number of tones each pilot tone in at least the payload is to shift from a current position.

11. The apparatus according to any of claims 8 to 10, wherein the second communication is an acknowledgement frame from a receiver of the first communication, and the request is represented in one or more bit values associated with the acknowledgement frame.

12. The apparatus according to any of claims 8 to 1 1 , wherein the second communication is a Bit Allocation Table (BAT) from a receiver of the first communication, the BAT including at least information related to a pilot tone sequence that is different than a pilot tone sequence associated with the first communication.

13. The apparatus according to any of claims 8 to 12, wherein the information is a plurality of payload pilot tone sequences that may be selected by a receiver of the first communication.

14. The apparatus according to any of claims 8 to 13, wherein the information is a plurality of frame pilot tone sequences that may be selected by a receiver of the first communication.