Patent Publication Number: US-2022231901-A1

Title: High-speed serial interface for orthogonal frequency division multiplexing (ofdm) cable modems

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims is a continuation of U.S. patent application Ser. No. 15/717,420 filed Sep. 27, 2017, which claims the benefit of priority under 35 U.S.C. § 119(e) to U.S. Patent Application Ser. No. 62/547,515 filed Aug. 18, 2017 by the same inventors and title as the present application, and which is fully incorporated herein by its reference. 
    
    
     FIELD 
     Embodiments of the present invention relate generally to, but not limited to, communication architectures and methods for communications between an analog front end (AFE) circuit and a digital modulator/demodulator system on a chip (SoC). 
     BACKGROUND 
     Certain communication systems use orthogonal frequency division multiplexing (OFDM), sometimes referred to as discrete multi-tone (DMT) transmission. One example of such OFDM communication system is defined by Data Over Cable Service Interface Specification (DOCSIS) 3.1, although the inventive embodiments are not limited thereto. A DOCSIS 3.1 cable modem is customer premises equipment (CPE) that facilitates a customer&#39;s, end-to-end digital communications with a network via a high frequency OFDM waveform propagated over a medium such as coaxial cable, fiber or potentially over-the-air (OTA). The cable modem includes both digital processing and “front-end” (i.e., first part of a receiver or transmitter interfaced with the transmission medium) analog processing components to accomplish this. Generally, for example, in a receiver, analog circuitry is used to amplify/de-amplify and frequency-convert signals so that they reach a suitable state to be converted into digital values, after which further signal processing can be performed in the digital domain. 
     With advances in the design and manufacture of integrated circuits (ICs) more and more traditional analog intermediate frequency (IF) signal processing tasksare handled digitally. Traditional analog tasks, like filtering and up-down conversion are now handled by means of digital filters and digital signal processors (DSPs), sometimes referred to, not necessarily identically because of design choices, as digitalradio processors, digital tuners, baseband processors, etc. It is noteworthy that many com systems have “mixed” signal processing designs where signals are processed in both analog and digital domains. 
     The migration of analog into digital circuits means that the choice of what front-end functions are implemented by analog and digital means generally is discretionary with a system architect and selected based on factors such as required performance, cost, size, and power consumption. Because of the mix of analog and digital technologies, OFDM transceivers generally have an analog front end (AFE) and a separate, digital radio processor/tuner to provide PHY and, if desired, medium access control (MAC) data link layer processing. In this case, the AFE and the digital tuner must have a data interface to accomplish downlink and uplink communications. Moreover, since manufacturers of analog components may differ from those providing digital tuner components, a common interface should be fast, dependable, standardized/uniform and/or known to others. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Certain circuits, logic operation, apparatuses and/or methods will be described by way of non-limiting example only, in reference to the appended Drawing Figures in which: 
         FIG. 1  shows a basic network diagram in which example embodiments of the invention may be utilized; 
         FIG. 2  shows a functional block diagram of a communication device according to various embodiments of the invention; 
         FIG. 3  shows a process for communicating OFDM channels between an analog front end (AFE) and digital radio according to one or more embodiments of the invention; 
         FIG. 4  shows a functional block diagram of an OFDM transceiver according to other embodiments; 
         FIGS. 5 and 6  show illustrative examples of downstream data and status frames according to various embodiments; 
         FIGS. 7 and 8  show illustrative examples of upstream data and status frames according to various embodiments; and 
         FIG. 9  shows an example functional block diagram of an OFDM-enabled modem with high speed serial interface according to one or more embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     While reference to example embodiments of the invention may be made to cable modems and related specifications, such as DOCSIS® 3.1 by Cable Television Laboratories, Inc., the high-speed serial interface of the inventive embodiments are not limited thereto and may be used in any protocols, applications or architectures where similar principles may be applied and their use provides similar advantages. Thus the specific description herein is provided only in context of one example implementation and the claims within are in no way limited thereby. 
     As shown in  FIG. 1  below, a basic network  100  is shown with a network node  110 , such as a cable provider Cable Modem Termination System (CMTS) or Internet service provider, which provides web access via an internet protocol (IP) interface to end user terminals  122 ,  124  including personal computers, laptops, wireless access points, via a network connection  112 , such as a combination of optical fiber from a service provider head end to an exchange terminal, transformed from optical to electrical signals and delivered to end users, generally over a coaxial cable though inventive embodiments are in no way limited to any particular network configuration. In order to receive, demodulate, and access signals from network node  110  in the downstream via connection  112 , end user terminals  122 ,  124 ,  126  may require customer premise equipment (CPE) such as a cable modem (CM)  115 . 
     A cable modem termination system or CMTS  100  is a piece of equipment, typically located in a cable company&#39;s headend or hubsite, which is used to provide high speed data services, such as cable Internet or Voice over Internet Protocol, to cable subscribers by way of their CM. 
     Referring to  FIG. 2 , a functional block diagram of a cable modem (CM) having a high-speed serial interface (HSIF) according to one or more inventive embodiments will now be explained. A cable modem  200  according to certain example embodiments, may include an analog front end (AFE) module  210  and a digital radio processor module  220 . A high-speed serial interface  224  provides 8b/10b encoded data and status framing between the analog and digital modules  210  and  220 . Optionally, digital tuner module  220  may include MAC layer functionality  250  as well. 
     In certain embodiments, the modem  200  and high speed serial interface (HSIF) between AFE  210  and digital radio  220  may support DOCSIS 3.1 with 12-bit I/Q 600 Msps sampling for handling 32 upstream and downstream OFDM channels. To this end, modem  200  HSIF may support two lanes for legacy quadrature amplitude modulation (QAM) DOCSIS channels between AFE  210  and digital radio  220 , another three lanes for 14-bit 250 Msps I/Q samples to transmit two OFDM channels in the downstream. 
     As an example, digital radio processor  220  may be implemented in some embodiments, as a System on a Chip (SoC) which includes PHY layer functionality  226 , e.g., PHY layer digital demodulation and decoding and, optionally, medium access control (MAC) layer  250  supporting networking functionality. The analog front end (AFE)  210 , in certain embodiments, may comprise a full spectrum sampling tuner that integrates low noise amplifier (LNA)/automatic gain control (AGC), analog/digital converters (ADCs/DACs), channelizers, power amplifiers, mixer, local oscillator (LO), phase locked loop(s) (PLL), etc., although specific functionalities of the AFE and digital radio processor may be modified to a designer&#39;s discretion. High-speed Serial Interface (HSIF)  224  is a system and protocol that carries digital data between analog front end (AFE)  210  and digital tuner  220  and vice versa. 
     In various embodiments, the HSIF serial interface  224  provides a digital transmission scheme which streams a plurality of 8b/10b encoded frames bi-directionally and which are constantly transmitted between AFE  210  and digital radio  220  through a serial bus connection (i.e., one in each direction, or “bi-directionally”). In one example embodiment, there are two types of frames send bi-directionally: a data frame; and a status frame. Status frames can be used either to deliver status information between AFE  210  and digital tuner  220 , or to serve as filler. In some embodiments, status frames may be used as fillers which are inserted asynchronously into the stream of frames to match the data rate to the HSIF serial rate (i.e. when there is no available data frame ready for transmission, a status frame is sent as a filler frame instead). 
       FIG. 3  shows an example process  300  high speed serial interface communications in an OFDM transceiver between an analog front end and digital radio processor may include forming  305  data and status frames to be transferred between the AFE and the digital radio, the data and status frames including a 10-bit comma sync word to identify the type of frame being sent, and for data frames, attaching a payload of a plurality of data samples (e.g.,  1 /Q digital samples in the downstream and digital data in the upstream). If  310  there is data or commands to be transferred in either direction, the data/command is placed in payloads of the frames and sent  315  over a bi-directional serial connection between AFE and digital radio. In preferred embodiments, data is transferred  315  in order of least significant bit (LSB) to most significant bit (MSB), with status frames transferred  315  periodically between data frames. If  310  no data is available for transfer, e.g., data frames are completed  315 , status frames may be sent  330 , preferably asynchronously, as filler frames between AFE and digital radio to mate the overall data throughput rate of the modem. In this manner, frames are continuously transferred through the HSIF so the overall OFDM transceiver data rate is matched by the high-speed serial interface. 
     Turning to  FIG. 4 , a more specific example embodiment of a communication device  400  operative to send/receive OFDM signals and compose and transfer data and status frames as discussed above, includes an analog front end (AFE)  410  for receiving and transmitting OFDM signals. In certain embodiments the AFE  410  includes a front end analog to digital downconverter  413  for analog down conversion of received OFDM signals, a downstream (D/S) framer  414  and a serializer  415 , the framer and serializer configured to frame and serialize the down converted digital samples and transfer them to digital radio circuit  420  in the frame formats and protocols discussed herein. In certain embodiments AFE  410  may further include an upstream (U/S) circuit portion having a deserializer  416 , a deframer  417  and an upconverter  418 , including a digital-to-analog converter (DAG) and programmable gain amplifier (PGA), operative to deserialize, deframe and upconvert digital data received from digital radio/tuner circuit  420  to analog form to send OFDM communications from modem  400 . 
     Similarly, digital radio  420  may include a deserializer  422 , a deframer  423  and downstream digital processing module  424  to process deframed digital I/Q samples from AFE  210 . Additionally, digital radio  420  may include upstream processing module  425 , framer  426  and serializer  427  for passing digital data to AFE  410  for transmission in OFDM channels. It is noted, that while various functional block items may be shown separately for functional understanding, actual components or circuitry may be combined in a same element. For example, a ser/des circuit may be a single circuit though depicted separately in  FIG. 4  similar to other functional block elements in AFE  210  and digital radio processor  220  as would be understood by one of ordinary skill in the art. 
     Referring to  FIGS. 5-8 , according to certain example embodiments, upstream and downstream frames  500 ,  600 ,  700 ,  800 , consist of a 10 bit K.28 Comma Sync word followed by a payload. In various embodiments, different K.28 words are used to distinguish between data (e.g., K28.5) and status (e.g., K28.1) frames. Also, in certain preferred embodiments, payloads of data frames are encoded using a standard 10/8-bit encoding. Therefore, the total length of frames (in bits) of these embodiments, is always a multiple of 10 (or 8 before encoding). In preferred embodiments, frames are fed least significant bit (LSB) first, to most significant bit (MSB) last, over a serial bus where Bit 0 refers to the LSB. Table 1 below shows an example embodiment for frame structure. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 HSIF Basic Frame Structure 
               
            
           
           
               
               
               
               
            
               
                 8-bit 
                   
                   
                   
               
               
                 words 
                 Name 
                 Content 
                 Description 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 Sync 
                 Sync placeholder. To 
                 Comma symbol is 
               
               
                   
                   
                 be converted to 10 bit 
                 always the first data in 
               
               
                   
                   
                 K28.5 orK28.1 symbol 
                 the stream. K28.5 is for 
               
               
                   
                   
                   
                 Data Frame. K28.1 is for 
               
               
                   
                   
                   
                 Status Frame 
               
               
                 1 
                 Header 
                 Packet Information 
                 Bits 7, 6 indicate that 
               
               
                   
                   
                 such as Data/Status, 
                 this frame is Data 
               
               
                   
                   
                 Valid/Invalid, 
                 Frame (11) or Status 
               
               
                   
                   
                 Reserved. 
                 Frame (00). 
               
               
                   
                   
                   
                 Bit 5 is Validity bit. Bit 
               
               
                   
                   
                   
                 5 = 1 is for a Valid 
               
               
                   
                   
                   
                 packet, Bit 5 = 0 is for 
               
               
                   
                   
                   
                 Invalid packet. 
               
               
                   
                   
                   
                 Bit 4 is frame parity 
               
               
                   
                   
                   
                 indication bit. Bit 4 = 1 is 
               
               
                   
                   
                   
                 for black frame. Bit 4 = 0 
               
               
                   
                   
                   
                 is for white frame 
               
               
                   
                   
                   
                 Bit 3 is reserved for 
               
               
                   
                   
                   
                 DAC turn and turn off 
               
               
                   
                   
                   
                 signaling 
               
               
                   
                 Payload 
                 Payload 
                 Data Payload 
               
               
                 2 
                 Parity 
                 Cyclic Redundancy 
                 Either CRC or RS 
               
               
                   
                   
                 Check (RC)16 or Reed 
                 encoding covering the 
               
               
                   
                   
                 Solomon (RS) encoding 
                 data bytes from Header 
               
               
                   
                   
                   
                 byte to the end of the 
               
               
                   
                   
                   
                 payload. 
               
               
                   
               
            
           
         
       
     
     Frame synchronization is achieved when the K.28 comma symbols are found in their nominal position S 1  times sequentially, where S 1  is preferably a programmable value. The nominal position (S 1 ) may depend on the mix of the data and status frames in the stream. The frame synchronization may considered to be lost when the frame synchronization symbol is not detected a specific number of times (S 2 ) in a specified number of consecutive frames (S 3 ), wherein S 2  and S 3  also preferably programmable. In certain preferred embodiments, an error in the sync word will not cause sync loss or packet loss. 
     In certain example embodiments, the payload of the frames may be followed by redundant bytes, which can be used for error detection and/or error correction. Example options of error detection/correction, referred to herein as “parity check” may include, cyclic redundancy check (CRC) that allows for frame detection only, or Reed Solomon forward error correction (FEC) block code, that will enable frame correction and/or detection. The specific parity check selected is in the discretion of the network architect based on the desired complexity and results. 
     Downstream Channelized Data Structure and Framing 
     An example embodiment of downstream data frame  500  is shown in  FIG. 5 . Here, the payload of the data frame  500  includes the complex baseband samples of two downstream RF OFDM channels sent through three logical lanes. Each logical lane carries I and Q samples of the two OFDM channels per assignment pattern in Table 2 below. 
     
       
         
           
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Sample arrangement of 2 OFDM channels over 3 logical lanes (Channel 
               
               
                 1 samples = numbers; Channel 2 samples = letters) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 Lane 1 
                 1 
                 3 
                 4 
                 6 
                 — 
                 — 
                 — 
               
               
                   
                 Lane 2 
                 2 
                 B 
                 5 
                 e 
                 — 
                 — 
                 — 
               
               
                   
                 Lane3 
                 a 
                 C 
                 d 
                 f 
                 — 
                 — 
                 — 
               
               
                   
                   
               
            
           
         
       
     
     The data rate for each channel is equal to 250 mega samples per second (Msps) per I as well as per Q of each channel. The rate of the complex samples rate over each logical lane is 250*2 channels/3 lanes Msps. In certain preferred embodiments, the format is 2&#39;s compliment. In case a certain channel is not active, zeros are transmitted instead of samples. 
     Assignment between the physical lanes to logical designations of Lane  1 , Lane  2 , Lane  3  should preferably be configurable on both the serial interface transmitter and receiver of the AFE and the digital radio. 
     Frame start times at the transmitter may preferably be aligned, and should start with the same color indication (e.g., black or white). Data samples are sent sequentially, while the color indication is toggled (e.g., black, white, black, white, etc.). The color of a frame is indicated in the header. In some preferred embodiments, the receiver will ensure that frames from the three lanes belong to the same color. It is assumed that skew between lanes will never be large enough to skip a frame. 
     Downstream data and status frame contents are shown in  FIGS. 5 and 6  as well as Tables 3 and 4 below: 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Downstream (DS) Data Frame Format 
               
            
           
           
               
               
               
            
               
                 8-bit 
                   
                   
               
               
                 words 
                 Content 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 Sync 
                 Data Frame Sync 
               
               
                 1 
                 Header 
                 Data Frame Header. LSB first, MSB 
               
               
                   
                   
                 last. 
               
               
                 238 
                 68 I/Q pairs of samples 
                 14 bits per sample. I first, Q second. 
               
               
                   
                   
                 LSB first, MSB last. 
               
               
                 2 
                 Parity 
                 Cyclic Redundancy Check (CRD) or 
               
               
                   
                   
                 Reed Solomon Forward Error 
               
               
                   
                   
                 Correction (FEC) Block Encoding 
               
               
                   
               
            
           
         
       
     
       FIG. 6  shows an illustrative example of a downstream status frame  600  according to various embodiments. Frame  600  may include the details in Table 4 below: 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Downstream (DS) Status Frame Format 
               
            
           
           
               
               
               
            
               
                 Bytes 
                 Name 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 Sync 
                 Status Frame Sync 
               
               
                 1 
                 Header 
                 Status Frame Header 
               
               
                 10 
                 Reserved 
               
               
                   
                 [Currently Unused, filled 
               
               
                   
                 with zeros] 
               
               
                 2 
                 Parity 
                 Cyclic Redundancy Check (CRC) or 
               
               
                   
                   
                 Reed Solomon Forward Error 
               
               
                   
                   
                 Correction (FEC) Block Encoding 
               
               
                   
               
            
           
         
       
     
     Each 8 bit word (Sync, Header and Parity) is also fed LSB first, MSB last. In some embodiments, the ratio of the data/status frames is 5:1 when the status frame size is 14. 
     Half Rate Mode (HM): 
     In Half Rate Mode, in one embodiment, the SerDes rate is 3 Gbps, half the rate of the Full Mode. The rate of the samples sent over each lane in this embodiment is equal to 250/3 Msps, which is exactly half of the rate of the Full Mode. The Half Rate frame structure is equal to structure for the Full Rate mode, except that the stuffing of samples into the payload of data frames is different as shown in Table 5 because only one OFDM channel is being framed. 
     
       
         
           
               
             
               
                 TABLE 5 
               
               
                   
               
               
                 Half Rate Channel to Lane Designation 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                 Lane 1 
                 1 
                 4 
                 7 
                 10 
                 — 
                 — 
                 — 
               
               
                   
                 Lane 2 
                 2 
                 5 
                 8 
                 11 
                 — 
                 — 
                 — 
               
               
                   
                 Lane 3 
                 3 
                 6 
                 9 
                 12 
                 — 
                 — 
                 — 
               
               
                   
                   
               
            
           
         
       
     
     Upstream DAG Data Structure and Framing 
     Example embodiments of upstream data frames  700  and status frames  800  are illustrated in  FIGS. 7 and 8 , respectively. In the upstream direction, samples are sent over the HSIF at a rate of 600 Msps, 15 bit samples,  710 . These upstream samples comprise a signal that includes all of the upstream channels modulated on their corresponding RF frequencies inside the upstream range. This data can be subsequently fed directly to the DAG for controlling (via status frame commands  810 , 812 ) and analog upconversion into OFDM RF channels (via data frames) by the AFE after deserializing and deframing through the high-speed serial interface. 
     In certain preferred embodiments for upstream Full Mode, all the samples from the digital radio are framed, serialized and sent through a two serial lanes, such that the odd samples are sent to one serial lane and the even samples are sent to the second serial lane. The AFE HSIF receiver preferably has a software programmable option to configure which lane is odd or even for upstream sampling. When not transmitting any data, the HSIF upstream (U/S) will send status frames as fillers. Again, the constant frame transmission upstream, with filler frames sent asynchronously when no data samples are needed to be sent, enables the HSIF transmission rate to match the overall upstream data rate. 
     In  FIG. 7 , an example upstream data frame  700  may include the information shown in Table 6 below: 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 UIS Data Frame Format 
               
            
           
           
               
               
               
            
               
                 8-bit 
                   
                   
               
               
                 words 
                 Name 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 Sync 
                 Data Frame Sync 
               
               
                 1 
                 Header 
                 Data Frame Header. LSB first, MSB 
               
               
                   
                   
                 last. 
               
               
                 120 
                 Data Samples 
                 FM: 64 even or odd consecutive 15-bit 
               
               
                   
                   
                 samples 
               
               
                   
                   
                 Each 15 bit sample is fed PATT, MSB 
               
               
                   
                   
                 last. 
               
               
                   
                   
                 DFM: 64 consecutive 15-bits samples 
               
               
                 2 
                 Parity 
                 CRC or RS FEC 
               
               
                   
               
            
           
         
       
     
     In  FIG. 8 , an example upstream status frame  800  may include the information shown in Table 6 below: 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 UIS Status Frame Format 
               
            
           
           
               
               
               
            
               
                 Bytes 
                 Name 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 1 
                 Sync 
                 Status Frame Sync 
               
               
                 1 
                 Header 
                 Status Frame Header 
               
               
                 6 
                 Reserved [filled with zeros] 
               
               
                 1 
                 POWER MODE 
                 A command to the AFE to enter 
               
               
                   
                 COMMAND 
                 acertain Power Saving Mode. 
               
               
                 1 
                 PGA GAIN 
                 Describes the last Gain that was 
               
               
                   
                   
                 sent to the PGA through a 
               
               
                   
                   
                 dedicated serial interface 
               
               
                 2 
                 Parity 
                 CRC or RS FEC 
               
               
                   
               
            
           
         
       
     
     According to certain embodiments, the upstream ratio of data/status frames is 3:1, when Status frame size is 12. 
     Decimated Half and Full Modes 
     In half mode framing and channel to logical lane assignments are identical except that the sample rate is scaled to 300 Msps. In decimated Full Mode samples are sent at 300 Msps over one lane. 
     The foregoing description of architecture and processing may be implemented as a system on a chip (SoC) receiver for cable modems using DOCSIS 3.1 Hybrid Fiber Coax OFDM standard although it is not limited thereto. Specific hardware and software implementations for high-speed serial interface embodiments discussed herein, may include designs in application specific integrated circuits (ASICs), micro-controllers, digital signal processors (DSPs), programmable logic arrays, and/or as software/firmware to perform the processes described herein. In one example embodiment, filter switching signal, synchronization and messaging may be programmed in software instructions and executed, or caused to be when in operation, by a processor, or central processing unit (CPU) attached to the hardware demodulator, AFE and/or distributed/dedicated processing engine. 
     Referring to  FIG. 9 , an example functional block diagram of a modem  900  for OFDM communications with HSIF may include a receive interface  902  adapted to receive a wired or wireless DOCSIS 3.1 OFDM signal into the modem, an analog frontend  905  and digital radio  910  connected to AFE  905  via a high-speed serial interface (HSIF) providing for the OFDM and legacy QAM channels as described herein. 
     In certain example embodiments, modem  900  may further include various other functional elements such as data link layer management circuit for packetization, managing flow control and higher layer levels of the OSI communications model, a processor/memory  912  adapted to control or provide processing/storage for various functional elements of modem  900  as desired. Furthermore, modem  900  may include security functionality  916  and client/user interface functionality  914 , such as 10-100 Gb based Ethernet PHY/MAC processing and respective interface(s) to provide a user TCP/IP layer interface connectivity. It should be understood that modem  900  is only a representational functional example and various additional functionalities may be included as desired or those functionalities shown omitted if not needed or desired as known by one of ordinary skill in the art. Thus the specific example depicted and described is not intended to limit the embodiments of the invention in any manner. 
     DOCSIS 3.1 OFDM has been engineered by Cablelabs and partners to increase the multi-gigabit data era on existing Hybrid Fiber-Coax (HFC) networks through improved spectral efficiency. Those of skill in the art would recognize modifications and substitutions of the elements, components and circuits described herein and possible and the invention is not limited to the specific examples in the detailed description but rather by the appended claims. 
     Example Embodiments 
     In a First Example Embodiments, a communication device in an orthogonal frequency division multiplexing (OFDM) enabled modem having an analog front end (AFE) and a digital radio may include: the AFE configured to send and receive OFDM modem channels, down convert received OFDM channels into a plurality of I and Q digital samples, the AFE including a high-speed serial interface (HSIF) to communicate the plurality of OFDM I and Q digital samples to the digital radio by continually generating and transferring downstream frames to the digital radio, wherein the downstream frames include data frames and status frames comprising a K.28 Comma Sync word followed by a payload. 
     According to a Second Embodiment, the communication device the First Embodiment is furthered wherein each frame comprises a plurality of 8/10b encoded words. 
     A Third Embodiment further defines the First wherein said downstream data frames include a frame sync, a header, 238 data payload words each including 68 I and Q digital sample pairs and wherein said downstream data frames including an error detection portion at their end. 
     A Fourth Embodiment may further define the Third wherein the error detection portion comprises one of a cyclic redundancy check (CRC) or Reed Solomon(RS) forward error correction block code. 
     A Fifth Embodiment further defines the First Embodiment wherein the HSIF of the AFE comprises a framer/deframer and a serializer/deserializer. 
     According to a Sixth Embodiment, the First Embodiment further includes the digital radio including a second HSIF comprising a second framer/deframer and a second serializer/deserializer. 
     In a Seventh Embodiment, the First Embodiment further is defined wherein the AFE and HSIF are configured to down convert two downstream OFDM channels at a 6 gigabit per second (Gbps) serial rate transfer to the digital radio in a full rate mode (FM). 
     In an Eighth Embodiment, the First Embodiment is furthered wherein the AFE and HSIF are configured to down convert one downstream OFDM channel at a 3 Gbps serial rate transfer to the digital radio in a half rate mode (HM). 
     According to a Ninth Embodiment, a device configured to communicate orthogonal frequency division multiplexed (OFDM) signals upstream and downstream with a network, the device including: a digital radio including a high speed serial interface (HSIF) to receive digital samples of two OFDM downstream radio frequency (RF) channels and digital samples of two downstream quadrature amplitude modulated (QAM) channels from a separately provided analog front end (AFE), the HSIF sending and receiving constant frames over a bi-directional serial connection to and from the AFE in the form of status and data frames, said status and data frames comprising a K.28 Comma Sync Word and a payload. 
     In a Tenth Embodiment, the Ninth Embodiment is furthered, wherein each frame comprises a plurality of 8/10b encoded words and wherein a K28.5 identifies the data frames and K28.1 identifies status frames. 
     An Eleventh Embodiment further defines the Ninth, wherein said downstream data frames include a frame sync, a header, 238 data payload words each including 68 I and Q digital sample pairs and wherein said downstream data frames including an error detection portion at their end. 
     A Twelfth Embodiment further adds to the Eleventh Embodiment wherein the error detection portion comprises one of a cyclic redundancy check (CRC) or Reed Solomon (RS) forward error correction block code. 
     According to a Thirteenth Embodiment, the Ninth Embodiment is furthered, wherein the HSIF of the digital radio comprises a framer/deframer and a serializer/deserializer. 
     A Fourteen Embodiment further defines the Thirteenth by including the AFE including a second HSIF comprising a second framer/deframer and a second serializer/deserializer. 
     A Fifteenth Embodiment furthers the Ninth, wherein the digital radio and HSIF are configured to sample, frame and serialize upstream data to send to the AFE at a 600 Mega samples per second (Msps) rate for 15-bit real samples fed least significant bit (LSB) first to most significant bit (MSB). 
     A Sixteenth Embodiment includes a method for communicating data in a cable modem using a high-speed serial interface (HSIF), the method including: forming downstream frames comprising a K28 Comma word and a payload; and continually transferring the formed downstream frames including status frames and data frames, the data frames including complex baseband samples for OFDM channels received by said cable modem in their payload, wherein when no data is needed to be transferred, status frames are inserted asynchronously as filler frames. 
     A Seventeenth Embodiment furthers the Sixteenth, wherein the OFDM channels received by said cable modem are compliant with a Data Over Cable System Interface Specification (DOCSIS) 3.1 standard. 
     An Eighteenth Embodiment furthers the method of the Seventeenth by further including receiving upstream frames continuously, said upstream frames including status and data frames, wherein said upstream data frames include 15 bit-data samples in their payloads. 
     According to a Nineteenth Embodiment, either the First or Second Embodiments are furthered, wherein said downstream data frames include a frame sync, a header, 238 data payload words each including 68 I and Q digital sample pairs and wherein said downstream data frames including an error detection portion at their end. 
     In a Twentieth Embodiment, the First through Third and Nineteenth Embodiment may be furthered, wherein the HSIF of the AFE comprises a framer/deframer and a serializer/deserializer. 
     A Twenty-First Embodiment may include any of the First through Third or Nineteenth through Twentieth Embodiments of a device that further includes: the digital radio including a second HSIF comprising a second framer/deframer and a second serializer/deserializer. 
     According to a Twenty-Second Embodiment, the First through Third or Nineteenth through Twenty-First Embodiments may be further defined, wherein the AFE and HSIF are configured to down convert two downstream OFDM channels at a 6 gigabit per second (Gbps) serial rate transfer to the digital radio in a full rate mode (FM). 
     A Twenty-Third Embodiment may further define the First through Third or Nineteenth through Twenty-Second Embodiments, wherein the AFE and HSIF are configured to down convert one downstream OFDM channel at a 3 Gbps serial rate transfer to the digital radio in a half rate mode (HM). 
     In a Twenty-Fourth Embodiment, the Ninth through Twelfth Embodiments are further defined, wherein the HSIF of the digital radio comprises a framer/deframer and a serializer/deserializer. 
     A Twenty-Fifth Embodiment further defines the Thirteenth by including the AFE and having a second HSIF comprising a second framer/deframer and a second serializer/deserializer. 
     According to a Twenty-Sixth Embodiment, a device for communicating data in a cable modem using a high-speed serial interface (HSIF), the device comprising: means for forming downstream frames comprising a K28 Comma word and a payload; and means for continually transferring the formed downstream frames including status frames and data frames, the data frames including complex baseband samples for OFDM channels received by said cable modem in their payload, wherein when no data is needed to be transferred, status frames are inserted asynchronously as filler frames. 
     A Twenty-Seventh Embodiment further defines the device of the Twenty-Sixth Embodiment by including means for receiving upstream frames continuously, said upstream frames including status and data frames, wherein said upstream dataframes include 15 bit-data samples in their payloads. 
     A Twenty-Eighth Embodiment further defines those of the Third and Eleventh Embodiments, wherein the error detection portion comprises one of a cyclic redundancy check (CRC) or Reed Solomon (RS) forward error correction block code. 
     According to a Twenty-Ninth Embodiment the embodiments of any one of the First through Fourth Embodiments is furthered wherein the HSIF of the AFE comprises a framer/deframer and a serializer/deserializer. 
     In a Thirtieth Embodiment, the device of any one of the First through Fifth and Twenty-Ninth Embodiments further includes: the digitial radio including a second HSIF comprising a second framer/deframer and a second serializer/deserializer. 
     A Thirty-First Embodiment may further any of the First through Fifth and Thirtieth Embodiments, wherein the AFE and HSIF are configured to down convert two downstream OFDM channels at a 6 gigabit per second (Gbps) serial rate transfer to the digital radio in a full rate mode (FM). 
     A Thirty-Second Embodiment furthers any one of the First through Fifth and Twenty Ninth through Thirty-First Embodiments, wherein the AFE and HSIF are configured to down convert one downstream OFDM channel at a 3 Gbps serial rate transfer to the digital radio in a half rate mode (HM). 
     A Thirty-Third Embodiment furthers the First through Fifteenth and Nineteenth through Thirty-Second Embodiments, wherein said cable modem is compliant with a Data Over Cable Service Interface Specification (DOCSIS) 3.1 standard. 
     A Thirty-Fourth Embodiment furthers any of the First through Fifteenth and Nineteenth through Thirty-Third Embodiments, wherein the digital radio comprises a System on a Chip (SoC) coupled to the AFE via a bi-directional serial interface. 
     Disclaimer: The present disclosure has been described with reference to the attached drawing figures, with certain example terms and wherein like reference numerals are used to refer to like elements throughout. The illustrated structures, devices and methods are not intended to be drawn to scale, or as any specific circuit or any in any way other than as functional block diagrams to illustrate certain features, advantages and enabling disclosure of the inventive embodiments and their illustration and description is not intended to be limiting in any manner in respect to the appended claims that follow, with the exception of 35 USC 112, sixth paragraph claims using the literal words “means for,” if present in a claim. 
     As utilized herein, the terms “component,” “system,” “interface,” “logic,” “circuit,” “device,” and the like are intended only to refer to a basic functional entity such as hardware, software (e.g., in execution), logic (circuits or programmable, firmware alone or in combination to suit the claimed functionalities. For example, a component, module, device or processing unit may mean a microprocessor, a controller, a programmable logic array and/or a circuit coupled thereto or other logic processing device, and a method or process may mean instructions running on a processor, firmware programmed in a controller, an object, an executable, a program, a storage device including instructions to be executed, a computer, a tablet PC and/or a mobile phone with a processing device. 
     By way of illustration, a process, logic, method or module can be any analog circuit, digital processing circuit or combination thereof. One or more circuits or modules can reside within a process, and a module can be localized as a physical circuit, a programmable array, a processor. Furthermore, elements, circuits, components, modules and processes/methods may be hardware or software, combined with a processor, executable from various computer readable storage media having executable instructions and/or data stored thereon. Those of ordinary skill in the art will recognize various ways to implement the logical descriptions of the appended claims and their interpretation should not be limited to any example or enabling description, depiction or layout described above, in the abstract or in the drawing figures.