The present embodiments relate generally to communication systems, and specifically to frame structure in communications using orthogonal frequency-division multiplexing (OFDM) or similar techniques.
The Ethernet Passive Optical Networks (EPON) protocol may be extended over coaxial (coax) links in a cable plant. The EPON protocol as implemented over coax links is called EPON Protocol over Coax (EPoC). Implementing an EPoC network or similar network over a cable plant presents significant challenges. For example, there is a need for efficient techniques to communicate information regarding channel structure and frame structure between a coax line terminal and coax network units.
Embodiments are disclosed in which a physical-layer (PHY) control channel that includes a plurality of contiguous subcarriers is used to communicate PHY control data between a coax line terminal (CLT) and coax network units (CNUs).
In some embodiments, a method of data communication is performed at a CNU coupled to a CLT. The CNU receives a plurality of OFDM symbols from the CLT and identifies a start-of-frame delimiter on a PHY control channel in the plurality of OFDM symbols. The PHY control channel includes a plurality of contiguous subcarriers. The CNU decodes one or more forward error correction (FEC) code words that follow the start-of-frame delimiter on the PHY control channel. The one or more FEC code words provide PHY control data that include information specifying a structure of a PHY frame that includes the plurality of OFDM symbols.
In some embodiments, a CNU includes a receiver to receive a plurality of OFDM symbols and identify a start-of-frame delimiter on a PHY control channel in the plurality of OFDM symbols. The PHY control channel includes a plurality of contiguous subcarriers. The CNU is also configured to decode one or more FEC code words that follow the start-of-frame delimiter on the PHY control channel. The one or more FEC code words provide PHY control data that include information specifying a structure of a PHY frame that includes the plurality of OFDM symbols.
In some embodiments, a method of data communication is performed at a CLT coupled to a plurality of CNUs. The CLT transmits a plurality of OFDM symbols to the plurality of CNUs. To transmit the plurality of OFDM symbols, the CLT places a start-of-frame delimiter on a PHY control channel in the plurality of OFDM symbols. The PHY control channel includes a plurality of contiguous subcarriers. The CNU also places one or more FEC code words on the PHY control channel following the start-of-frame delimiter. The one or more FEC code words provide PHY control data that include information specifying a structure of a PHY frame that includes the plurality of OFDM symbols.
In some embodiments, a CLT includes a transmitter to transmit a plurality of OFDM symbols. The transmitter is configured to place a start-of-frame delimiter on a PHY control channel in the plurality of OFDM symbols. The PHY control channel includes a plurality of contiguous subcarriers. The transmitter is further configured to place one or more FEC code words on the PHY control channel following the start-of-frame delimiter. The one or more FEC code words provide PHY control data that include information specifying a structure of a PHY frame that includes the plurality of OFDM symbols.
The present embodiments are illustrated by way of example and are not intended to be limited by the figures of the accompanying drawings.
Like reference numerals refer to corresponding parts throughout the drawings and specification.
In the following description, numerous specific details are set forth such as examples of specific components, circuits, and processes 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. The present embodiments are not to be construed as limited to specific examples described herein but rather to include within their scope all embodiments defined by the appended claims.
The CLT 162 transmits downstream signals to the CNUs 140-1, 140-2, and 140-3 and receives upstream signals from the CNUs 140-1, 140-2, and 140-3. In some embodiments, each CNU 140 receives every packet transmitted by the CLT 162 and discards packets that are not addressed to it. The CNUs 140-1, 140-2, and 140-3 transmit upstream signals using coax resources specified by the CLT 162. For example, the CLT 162 transmits control messages (e.g., GATE messages) to the CNUs 140-1, 140-2, and 140-3 specifying respective future times at which and respective frequencies on which respective CNUs 140 may transmit upstream signals. The bandwidth allocated to a respective CNU by a control message may be referred to as a grant. In some embodiments, the downstream and upstream signals are transmitted using orthogonal frequency-division multiplexing (OFDM). For example, the upstream signals are orthogonal frequency-division multiple access (OFDMA) signals and the downstream signals include modulation symbols on different groups of subcarriers that are directed to different CNUs 140.
In some embodiments, the CLT 162 is part of a fiber-coax unit (FCU) 130 that is also coupled to an optical line terminal (OLT) 110, as shown in
In some embodiments, each FCU 130-1 and 130-2 includes an ONU 160 coupled with a CLT 162. The ONU 160 receives downstream packet transmissions from the OLT 110 and provides them to the CLT 162, which forwards the packets to the CNUs 140 (e.g., CNUs 140-4 and 140-5, or CNUs 140-6 through 140-8) on its cable plant 150 (e.g., cable plant 150-1 or 150-2). In some embodiments, the CLT 162 filters out packets that are not addressed to CNUs 140 on its cable plant 150 and forwards the remaining packets to the CNUs 140 on its cable plant 150. The CLT 162 also receives upstream packet transmissions from CNUs 140 on its cable plant 150 and provides these to the ONU 160, which transmits them to the OLT 110. The ONUs 160 thus receive optical signals from and transmit optical signals to the OLT 110, and the CLTs 162 receive electrical signals from and transmit electrical signals to CNUs 140.
In the example of
In some embodiments, the OLT 110 is located at a network operator's headend, the ONUs 120 and CNUs 140 are located at the premises of respective users, and the FCUs 130 are located at the headends of their respective cable plants 150 or within their respective cable plants 150.
The coax PHY 212 in the CLT 162 is coupled to a media access controller (MAC) 206 (e.g., a full-duplex MAC) by a media-independent interface 210 and a reconciliation sublayer (RS) 208. In some embodiments, the media-independent interface 210 is a 10-Gigabit Media-Independent Interface (XGMII). The MAC 206 is coupled to a multi-point control protocol (MPCP) implementation 202, which includes a scheduler 204 that schedules downstream and upstream transmissions.
The coax PHY 224 in the CNU 140 is coupled to a MAC 218 (e.g., a full-duplex MAC) by a media-independent interface 222 (e.g., an XGMII) and an RS 220. The MAC 218 is coupled to an MPCP implementation 216 that communicates with the MPCP implementation 202 to schedule upstream transmissions (e.g., by sending REPORT messages to the MPCP 202 implementation and receiving GATE messages in response).
In some embodiments, the MPCP implementations 202 and 216 are implemented as distinct sub-layers in the respective protocol stacks of the CLT 162 and CNU 140. In other embodiments, the MPCP implementations 202 and 216 are respectively implemented in the same layers or sub-layers as the MACs 206 and 218.
Communication between a CLT 162 and respective CNUs 140 on a cable plant 150 may be performed using frequency-division duplexing (FDD) or time-division duplexing (TDD). For FDD, upstream and downstream transmissions use different frequency bands and therefore may be simultaneous. For TDD, upstream and downstream transmissions share one or more frequency bands, with upstream transmissions occurring at different times (e.g., in different time windows) than downstream transmissions.
In some embodiments, the channel on which the PHY frames 302 are transmitted includes a minimum guaranteed continuous frequency band 306 (a “guaranteed band 306”). There are no exclusion bands within the guaranteed band 306. However, some subcarriers within the guaranteed band 306 may not be used for data transmission. Alternatively, there are no nulled subcarriers within the guaranteed band 306 in accordance with some embodiments. Examples of the width of the guaranteed band 306 include, but are not limited to, 6 MHz, 12 MHz, and 24 MHz. While the location of the guaranteed band 306 in the available frequency spectrum remains fixed with respect to a sequence 300 of PHY frames 302, it may change over time (e.g., it may be changed periodically).
The PHY frames 302 include a PHY link channel (PLC) 308. The PHY link channel 308 is an example of a PHY control channel. A specified number of subcarriers may be reserved for the PHY link channel 308. The number of subcarriers in the PHY link channel 308 is thus predefined. In one example, the PHY link channel 308 includes eight subcarriers. In some embodiments, the PHY link channel 308 is at the center of the guaranteed band 306. The PHY link channel 308 may be used to communicate PHY control data between a transmitter (e.g., in the coax PHY 212 of a CLT 162,
The PHY frames 302 may also include continual pilot symbols 310 on one or more subcarriers. The continual pilot symbols 310 are known modulation symbols. In some embodiments, one or more pairs of continual pilot symbols 310 are placed symmetrically about the PHY link channel 308. Each such pair thus has mirror symmetry about the PHY link channel 308. Two such pairs of continual pilot symbols 310 are shown in
The continual pilot symbols 310 are said to be continual because they are present on their respective subcarriers in each OFDM symbol 304 of each PHY frame 302. PHY frames 302 may also include non-continual pilot symbols on specified subcarriers. For example, two OFDM symbols 304 (e.g., the first and second OFDM symbols 304) of a respective PHY frame 302 may include additional pilot symbols on a specified set of subcarriers (e.g., on every subcarrier or every other subcarrier).
The PHY link channel 308 may include a start-of-frame delimiter 312, which is also referred to as a preamble, at the beginning of respective PHY frames 302 (e.g., the beginning of each PHY frame 302). The start-of-frame delimiter 312 is used to identify the beginning of the respective PHY frames 302. The start-of-frame delimiter 312 includes known modulation symbols placed on subcarriers in the PHY link channel 308 in a specified number of OFDM symbols 304 (e.g., three OFDM symbols 304, as shown in
The downstream windows 406 in a PHY frame 402 include a specified number of OFDM symbols 304. (Each column in each downstream window 406 of
Continual pilot symbols 414 may be included in the downstream windows 406. In the context of TDD, pilot symbols are said to be continual if they are present on their respective subcarriers in each OFDM symbol 304 of the downstream windows 406. One or more respective pairs of continual pilot symbols 414 may be symmetric about a PHY link channel 412. The PHY link channel 412 is another example of a PHY control channel.
The PHY link channel 412 includes a specified number of subcarriers (e.g., eight subcarriers) in the downstream windows 406. As described for the PHY link channel 308 (
In some embodiments, information conveyed by the PHY link channel 412 is encoded into forward error correction (FEC) code words (CWs) 416.
In some embodiments, a first code word 416 conveyed on the PHY link channel 412 in a PHY frame 402 is followed by a longer second code word 416, as shown in
In some embodiments, a respective PHY frame 402 includes a single FEC code word 416 that extends across multiple TDD cycles 404 (or portions thereof), as shown in
In the example of
Attention is now directed to an initial acquisition sequence in accordance with some embodiments. This sequence may be performed by a CNU 140 (
Data from the PHY control channel (e.g., PLC 308,
An admission process is performed to register the CNU 140 with the CLT 162. Ranging (e.g., including round-trip time measurement) is performed to determine a timing advance for the CNU 140. Finally, the CNU 140 begins to transmit data to the CLT 162.
In some embodiments, the plurality of OFDM symbols 304 is transmitted during downstream windows 406 in respective TDD cycles 404 (
In some embodiments, a plurality of FEC code words 416 is placed on the PHY control channel following the start-of-frame delimiter in operation 606. The plurality of FEC code words 416 includes an initial FEC code word 416 (e.g., as shown in
In some embodiments, the PHY frame that includes the plurality of OFDM symbols 304 transmitted in operation 602 includes a first TDD cycle 404 and a second, following TDD cycle 404. A plurality of FEC code words 416 is placed on the PHY control channel following the start-of-frame delimiter 312 in operation 606. The plurality of FEC code words 416 includes a first group of FEC code words 416 on the PHY control channel in the first TDD cycle 404 and a second group of FEC code words 416 on the PHY control channel in the second TDD cycle 404 (e.g., as shown in
A CNU 140 receives (610) the plurality of OFDM symbols 304. For example, the OFDM symbols 304 are received in the downstream windows 406 in respective TDD cycles 404 (
In some embodiments, the CNU 140 detects (612) the one or more pairs of continual pilot symbols (e.g., continual pilot symbols 310,
The CNU 140 identifies (616) the start-of-frame delimiter 312 on the PHY control channel in the plurality of OFDM symbols. The CNU 140 may use the start-of-frame delimiter 312 to estimate (618) the channel. The start-of-frame delimiter 312 may also be used for PHY frame synchronization and TDD cycle alignment.
The CNU 140 decodes (620) the one or more FEC code words 416. PHY control data is extracted from the one or more FEC code words 416 and used to facilitate communications with the CLT 162.
The method 600 includes a number of operations that appear to occur in a specific order. It should be apparent, however, that the method 600 can include more or fewer operations, which can be executed serially or in parallel. An order of two or more operations may be changed, performance of two or more operations may overlap, and two or more operations may be combined into a single operation.
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 spirit and 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.
This application claims priority to U.S. Provisional Patent Application No. 61/813,036, titled “PHY Link Channel Structure,” filed Apr. 17, 2013, which is hereby incorporated by reference in its entirety.
Number | Date | Country | |
---|---|---|---|
61813036 | Apr 2013 | US |