Patent Publication Number: US-7908625-B2

Title: Networked multimedia system

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     The present application incorporates by reference in its entirety herein U.S. provisional application having Ser. No.: 60/416,155, which was filed on Oct. 4, 2002, and U.S. provisional application having Ser. No.: 60/424,269, which was filed on Nov. 6, 2002. Also, the present application is a continuation-in-part of copending U.S. patent applications having Ser. Nos. 10/263,160, 10/263,449, and 10/263,270, which were filed on Oct. 2, 2002 and are assigned to a common assignee, the teachings of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to broadband communications systems, and more particularly, to the field of set-top terminals and a networked multimedia system. 
     DESCRIPTION OF THE RELATED ART 
     Broadband communications systems, such as satellite and cable television systems, are now capable of providing many services in addition to analog broadcast video. In implementing enhanced programming, the set-top terminal (STT), otherwise known as the set-top box, has become an important computing device for accessing various video services. In addition to supporting traditional analog broadcast video functionality, many STTs now also provide other functionality, such as, for example, an interactive program guide (IPG), video-on-demand (VOD), subscription video-on-demand (SVOD) and functionality traditionally associated with a conventional computer, such as e-mail. Recently new functionality has been added to conventional STTs—namely the ability to video record an incoming video stream in digitized form onto a mass storage device such as a hard dish drive, and playback that recorded video as desired by the user. This functionality has become known as a “digital video recorder” (DVR) or personal video recorder (PVR) and is viewed as a superior alternative to conventional video tape recorders for capture and subsequent playback of programming content. 
     An STT is typically connected to a communications network (e.g., a cable or satellite television network) and includes hardware and software necessary to provide various services and functionality. Preferably, some of the software executed by an STT is downloaded and/or updated via the communications network. Each STT also typically includes a processor, communication components, and memory, and is connected to a television or other display device. While many conventional STTs are stand-alone devices that are externally connected to a television, an STT and/or its functionality may be integrated into a television or other device, as will be appreciated by those of ordinary skill in the art. 
     An STT is typically connected to a television set and located at the home of the cable or satellite system subscriber. Since the STT is located in the subscriber&#39;s premises, it typically may be used by two or more users (e.g., household members). Television has become so prevalent in the United States, however, that the typical household may have two or more television sets, each television set requiring its own STT if the subscriber wishes to have access to enhanced functionality. However, STTs can be expensive and users may not be willing to purchase additional expensive STTs. This is particularly true of STTs incorporating PVR functionality since such devices require not only the addition of a hard disk drive but also additional processing components and software. 
     Therefore, there exists a need for systems and methods for addressing these and/or other problems associated with STTs. Specifically, there exists a need for systems and methods that allow multiple subscribers operating discrete STTs within a subscriber premises or other local area to have access to programming and content received by and/or stored in another STT. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. In the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a simplified block diagram depicting a non-limiting example of a conventional broadband communications system. 
         FIG. 2  is a block diagram illustrating one preferred embodiment of a networked multimedia system (NMS) in accordance with the present invention. 
         FIG. 3  is a simplified, non-limiting block diagram illustrating selected components of a primary STT in accordance with one preferred embodiment of the present invention. 
         FIG. 4  illustrates an example of a graph of the frequencies of the downstream broadband signals and the predetermined frequencies of the up-converted selected signals. 
         FIG. 5  is a simplified diagram of one preferred embodiment of a remote STT device. 
         FIG. 6  is a block diagram illustrating one preferred embodiment of a QPSK transmitter that converts user input command signals into FSK signals for transmission to the splitter/isolation module (SIM). 
         FIG. 7  illustrates generation of an FSK signal for input serial data x(n)=[10010]. 
         FIG. 8  illustrates a second embodiment of the present invention for transmitting reverse command signals as OOK signals over the coaxial cable to the SIM. 
         FIG. 9  illustrates a block diagram of a second embodiment of the SIM  210  comprising passive splitter/isolation components in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the invention can be understood in the context of a broadband communications system and a local network. Note, however, that the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. For example, transmitted broadband signals include at least one of video/audio, telephony, data, or Internet Protocol (IP) signals, to name but a few. Furthermore, remote devices included in the broadband communications system receiving the transmitted broadband signals may include a remote set-top terminal, a television, a consumer electronics device such as a DVD player/recorder, a computer, a personal digital assistant (PDA), or other device. All examples given herein, therefore, are intended to be non-limiting and are provided in order to help clarify the description of the invention. 
     The present invention is directed towards a networked multimedia system (NMS) that is suitable for use in a broadband communications system. The NMS is typically located within a subscriber premise. It will be appreciated, however, that the NMS can also be used in a multi-unit dwelling, business, school, hotel, or hospital, among others. Advantageously, the NMS allows the premise to be locally networked (i.e., home-networked). In accordance with the present invention a primary set-top terminal (STT) typically receives and forwards broadband multimedia content signals (e.g., digital or analog cable television channels (i.e., audio/video signals), IP signals, VOD signals, software application signals, administrative signals, etc.) throughout the local network to a plurality of remote devices. Additionally, the remote devices are each capable of requesting from the primary STT and seamlessly receiving, for example, a cable channel, a stored or recorded presentation, a VOD movie, or the interactive program guide, just as if the remote devices were equipped with the primary STT functionality. In other words, the remote devices may be simplified, less-costly versions of the primary STT but are capable of utilizing, via the local network, some or all of the advanced hardware and software features, such as memory, a mass storage device, or software applications, that are available in the primary STT. A broadband communications system that is suitable in implementing a preferred embodiment of the present invention is described hereinbelow. 
     An Example of a Broadband Communications System 
       FIG. 1  is a simplified block diagram depicting a non-limiting example of a conventional broadband communications system  100 . In this example, the communications system  100  includes a headend  110  that is coupled to a local network (LN)  101  via a communications network (CN)  130 . The CN  130  may be any network that is suitable for transmitting preferably downstream and upstream broadband multimedia signals, such as audio/video signals, IP signals, telephony signals, or data signals to name but a few. The CN  130  may be, for example, a hybrid fiber/coax (HFC) network, a fiber-to-the-home (FTTH) network, a satellite network, or a fixed wireless network (e.g., MMDS), among others. 
     The LN  101  includes a set-top terminal (STT)  105  that provides the broadband signals to the remote devices  140 - 1  and  140 - 2 , and, optionally, to additional remote devices including, for example, remote device  140 - 3 . The STT  105  may be coupled to the remote devices either directly or via one or more other devices. It will be appreciated that the STT  105  may be a stand-alone unit or may be integrated into another device, such as, for example, a television or a computer. Additionally, the remote devices may be located in different rooms than where the STT  105  is located. Further information regarding the LN  101  is provided in copending U.S. patent application Ser. Nos. 10/263,160; 10/263,270; and 10/263,449, which were filed on Oct. 2, 2002, the disclosure and teachings of which are hereby incorporated in their entirety by reference. 
     The headend  110  may include one or more server devices (not shown) for providing video, audio, and/or data signals to the STT  105  via the CN  130 . The headend  110  and the STT  105  cooperate to provide a user with a variety of services via the remote devices  140 -i (e.g.,  140 - 1 ,  140 - 2 , and/or  140 - 3  ). The services may include, for example, analog or digital television services and channels, video-on-demand (VOD) services, and/or pay-per-view (PPV) services, among others. Each broadcast television channel typically provides a sequence of television presentations corresponding to a television station (e.g., ABC, NBC, CBS, or FNN, to name a few) and is typically identified by a channel number (e.g., channel  2 , channel  3 , channel  4 , etc.). Additionally, a television station (e.g., the Fox News Network) that is identified by a certain channel number (e.g., channel  84 ) to viewers served by a first service provider may be identified by another channel number (e.g., channel  45 ) to viewers served by a second service provider. 
     A preferred embodiment of the present invention may be implemented in addition to or replacement of the local network  101  of  FIG. 1 . The present invention will now be described in detail. 
       FIG. 2  is a block diagram illustrating one preferred embodiment of a networked multimedia system (NMS)  200  in accordance with the present invention. The NMS  200  includes a master or primary STT  205 , a splitter/isolation module (SIM)  210 , and a plurality of remote devices, e.g.,  215 - 1 ,  215 - 2 ,  215 -n. It is to be noted that while the embodiment of  FIG. 2  illustrates an NMS having but two remote devices, the invention is not so limited. Indeed, any number of such remote devices may be employed, consistent with the requirements and capabilities of the NMS, as described herein. Briefly, the SIM  210  receives downstream broadband signals from, for example, the headend or satellite and subsequently provides the downstream signals to the primary STT  205  or to both the primary STT  205  and any one or all of the plurality of remote devices  215 -n depending on the implementation. Upon command, the primary STT  205  may also forward selected real-time downstream signals or stored signals to one or all of the remote devices  215 -n via the SIM  210 . More specifically, the plurality of remote devices  215 -n communicates with the primary STT  205  by sending reverse control/command signals via coaxial cable  220 ,  221 -n requesting stored presentations or real-time signals. It will be appreciated that other wired mediums, such as telephone lines or data cables, may be used so long as the transport format accommodates the desired transmission medium. Advantageously, in accordance with the present invention, the plurality of remote devices  215 -n have access to all of the primary STT&#39;s hardware and software functionality, along with receiving downstream signals directly from the headend via the SIM  210 . In this manner, the remote devices  215 -n may have limited functionality, thereby decreasing the overall costs to the service provider and the subscriber while offering advanced services to all of the remote devices that are networked. 
     Furthermore, the primary STT  205  may also directly provide broadband signals to a coupled local device  225 , which may be, for example, a television, computer, or PDA. It will be appreciated that the primary STT  205  may transmit signals to and receive control signals from the local device  225  via wireless devices (e.g., RF or IR devices) or a wired medium (e.g., coaxial cable, power lines, or telephone lines). It will also be appreciated that the primary STT  205  may be incorporated in the local device  225 . The primary STT  205  optionally includes, for example, an IR receiver  368  ( FIG. 3 ) for receiving user input control signals (e.g., signals indicating a channel change, IPG display, volume control, or administrative signals) that are encoded in an IR signal. Those of ordinary skill in the art would understand elements and operation of a typical IR receiver  368 . Further information regarding the transmitting and receiving of signals between the primary STT and the coupled local device via wireless devices or a wired medium can be found in copending U.S. patent application Ser. No. 10/008,581, the teachings of which are hereby incorporated by reference. 
     A Preferred Embodiment of the Primary STT  205   
       FIG. 3  is a simplified, non-limiting block diagram illustrating selected components of a primary STT  205  in accordance with one preferred embodiment of the present invention. In other embodiments, a primary STT  205  may include only some of the components shown in  FIG. 3 , in addition to other components that are not shown in  FIG. 3 . The primary STT  205  has electronic components (e.g., processor  305 , memory  310 , etc.) that are coupled to a local interface  315 , which can include, for example, one or more buses or other wired or wireless connections. The processor  305  is a hardware device for executing software, particularly that stored in memory  310 . The processor  305  can be a custom-made or commercially available processor for executing software instructions. When the primary STT  205  is in operation, the processor  305  is configured to execute software stored within the memory  310 , to communicate data to and from the memory  310 , and to generally control operations of the primary STT  205  according to the software. 
     The memory system  310  may include any one or combination of volatile memory elements (e.g., random access memory (RAM), dynamic RAM (DRAM), static RAM (SRAM), synchronous DRAM (SDRAM), magnetic RAM (MRAM), etc.) and nonvolatile memory elements (e.g., read only memory (ROM), hard drive, tape, compact disc ROM (CD-ROM), etc.). Moreover, the memory system  310  may incorporate electronic, magnetic, optical and/or other types of storage multimedia. Note that the memory system  310  can have a distributed architecture, where various memory components are situated remotely from one another, but can be accessed by the processor  305 . 
     The software in memory  310  may include one or more separate programs, each of which comprises executable instructions for implementing logical functions. In the example of  FIG. 3 , the software in memory  310  includes an operating system (OS)  320 , a WatchTV application  321 , a navigator application  322 , a personal video recorder (PVR)/digital video recorder (DVR) application  323 , a driver  324 , a VOD application  325 , and an IPG application  326 , among others. The OS  320  controls the execution of other software and provides management and control services including, for example, scheduling, input-output control, file and data management, memory management, and communication control. The WatchTV application  321  is used to help provide a user with a requested broadcast television channel. The EPG application  326  provides an interactive program guide that mainly includes listings of television channels provided by the primary STT  205 , but may also present additional services, such as an NMS interactive guide. The navigator application  322  is used to route user input commands to respective software applications that have registered with the navigator application  322  to receive the respective commands. The VOD application  325  provides a user with video-on-demand presentations, such as, for example, movies that are selected via an on-screen movie catalog. The PVR application  323  may provide user interface (UI) screens that can be used to manage (e.g., record, playback, and delete) the content of a storage device  330 . Accordingly, the PVR application  323  may record or delete data from the storage device  330  with the help of a software driver  324 , which controls read and write operations performed on the storage device  330 . In one preferred embodiment, the storage device  330  includes a hard drive that reads from and writes to a hard disk. It will be appreciated that other software applications may be included in memory  310 . 
     A tuner system  335  includes, in one implementation, an out-of-band tuner (not shown) for receiving out-of-band signals (e.g., administrative signals that were modulated using quadrature phase shift keying (QPSK)), and a plurality of in-band tuners  340 -n (e.g., quadrature amplitude modulation (QAM)/analog tuners) for receiving analog and/or digital in-band television channels. Alternatively, the tuner system  335  may only include one in-band tuner depending on a desired implementation. A signal processing system  345  may be capable of demodulating, demultiplexing, decrypting, and decoding signals that are tuned to by the tuner system  335 . Although shown as one module, the signal processing system may comprise multiple modules that are located in different parts of the primary STT  205 . It will be appreciated that in the preferred embodiment of the present invention the number of tuners  340 -n typically corresponds to at least the optional coupled local device(s)  225  and the storage device  330 . Further information regarding adding additional tuners can be found in copending U.S. patent application Ser. No. 10/263,449, which was filed on Oct. 2, 2002, the teachings of which are hereby incorporated by reference. 
     The primary STT  205  also includes an upstream transmitter  350  and a local transmitter  355 . The upstream transmitter  350 , which may alternatively be included in the tuner system  335 , preferably includes a QPSK/QAM modulator (not shown) that is used to transmit the upstream data to the CN  130  ( FIG. 1 ). The local transmitter  355  preferably includes a UHF (ultra high frequency) modulator for modulating, for example, a television channel that is output to the local device  255  ( FIG. 2 ) through an optional interface  365 , such as for example an Ethernet wireless device, depending on a desired implementation. 
     The primary STT  205  may also include an IR receiver  368 , a remote device command receiver  285 , and/or an RF receiver  375 , which detect respective signals (IR, electric, or wireless RF) having encoded remote control commands requesting television services, channels, or other NMS services. In one embodiment, the remote device command receiver  285  may forward received remote control signals from the plurality of remote devices  215 -n to the processor  305 , which then, for example, routes the commands to respective applications for processing. 
     An output system  380  may be used to encode television services that are to be output to, for example, local device  225  ( FIG. 2 ), which may be a television or computer, via the connection  111 . The output system  380  may provide a television  225  with signals that are in, for example, NTSC (National Television Standard Committee) format. In another embodiment, if the television  225  is a digital television, for example, a high definition television (HDTV), then the output system may include an MPEG (Motion Picture Expert Group) encoder for encoding television service signals in an MPEG-2 format. It will be appreciated that the primary STT  205  may also provide multimedia content signals to other remote devices (e.g., a computer, a remote set-top terminal, or a PDA) located in the network, such as illustrated in  FIG. 1 . 
     Referring to  FIG. 2  in conjunction with  FIG. 3 , the primary STT  205  receives via the SIM  210  downstream broadband signals (i.e., signals that are typically in the range from 45 MHz to 870 MHz). A low pass filter in diplex filter  235  provides the downstream signals to the tuner system  335  and the remote device command receiver  285 . Upon command from the processor  305 , the tuner system  335  may send the downstream signals to any local devices  225 , the storage device  330  for optional storage, and additionally to a modulator  240 . More specifically, the processor  305  instructs the tuner system  335  to extract specified content signals from the downstream signals. By way of example, a tuner  340  responsive to the coupled local device  225  provides selected content signals directly to the local device  225 . The tuner  340  or a plurality of tuners  340 -n that are responsive to a remote device  215 -n via the processor  305  may forward selected real-time presentations directly to the modulator  240  for transmission to the plurality of remote devices  215 -n. Furthermore, upon user input from the primary STT  205  or any one of the remote devices  215 -n, the processor  305  may instruct the tuner system  335  to provide content presentations to the storage device  330  for storage. The stored presentations are subsequently available for forwarding to any of the remote devices  215 -n and/or the local device  255  upon instruction from the processor  305 . User input signals will be discussed in further detail hereinbelow relating with a preferred embodiment of the remote devices  215 -n. 
     In accordance with the present invention, the modulator  240  modulates the selected content signals (i.e., NMS presentations) provided from either the tuner system  335  or the storage device  330  prior to forwarding to the SIM  210 . For example, a preferred embodiment of the present invention uses a QAM modulator, which may be used for effectively transmitting signals over coaxial cable in a cable television environment. Other embodiments may include a QPSK modulator in a satellite environment, an 8VSB (8-vestigial sideband) modulator in a digital terrestrial environment in the U.S., and a COFDM (coded orthogonal frequency division multiplexing) modulator in a digital terrestrial environment in Europe, or alternatively an analog modulator. The modulator  240  converts the signals to a predetermined intermediate frequency. Subsequently, the modulated presentations are up-converted to a predetermined higher frequency that is preferably greater than the highest frequency used in the system with, for example, a UHF converter  245 .  FIG. 4  illustrates an example of a graph of the conventional frequencies of the downstream broadband signals  403  and the predetermined frequencies of the up-converted NMS presentations  405 . A preferred embodiment of the present invention is to up-convert the NMS presentations to an available high frequency channel, for example, channel 134, which may have a frequency range from 852 MHz to 858 MHz. The service provider, therefore, would provide downstream signals in the range from 45 MHz to approximately 840 MHz, thereby leaving frequencies greater than 840 MHz available for the transmission of NMS presentations. Accordingly, the NMS presentations  405  do not interfere with the downstream signals that may be concurrently provided via the common coax  220 ,  221 -n to the primary STT  205  and the remote devices  215 -n. It will be appreciated that other frequency ranges can be used that are either in-band (e.g., from 45 MHz to 860 MHz) or out-of-band (e.g., from 865 MHz to 1 GHz) so long as the predetermined frequency range is not used for transmission of the downstream signals or is within the range that is tunable by the plurality of remote devices  215 -n. The up-converted NMS presentations are subsequently provided to the SIM  210  via a high pass filter in the diplex filter  235 . 
     Furthermore, the remote device command receiver  285  is included in the primary STT  205  for receiving reverse NMS command signals from the plurality of remote devices  215 -n. Command signals will be discussed further hereinbelow; however, the command signals can be transmitted in the form of on-off keying (OOK) signals, frequency shift keying (FSK) signals, or serial data transmissions, among others. The remote device command receiver  285 , therefore, includes the respective demodulator, such as an OOK demodulator or an FSK demodulator that demodulates the signals as known to one skilled in the art. 
     Additionally, an optional DC source  280 , which may supply, for example, 12 to 15 volts (V) and 200 milliamps (mA), may be provided to power an amplifier  275  located the SIM  210 , if necessary. If required, the amplifier  275  amplifies the downstream signals received from the CN  130 . It will be appreciated that if the SIM  210  is a passive splitter/isolation module, the DC source  280  is not necessary. 
     Preferred Embodiments of the SIM  210   
     Referring again to  FIG. 2 , the selected NMS presentations are provided by the primary STT  205  to the SIM  210  via the coaxial cable  220 . In a first embodiment of the lo SIM  210 , the selected NMS presentations are routed to the plurality of remote devices  215 -n via a diplex filter  250 . A splitter  266  provides the NMS presentations to HPF  255 , which subsequently provides the filtered NMS presentations to splitter  267 , diplex filter  260 , and splitter  265 . The high pass filter (HPF)  255  has low attenuation at the frequencies of the NMS presentation and high isolation at lower frequencies, and thus, provides high isolation between port  268  and ports  269 -n at these lower frequencies. It will be appreciated that a bandpass filter (BPF) can alternatively be used depending on the transmission frequencies of the NMS presentations. Splitter  265  provides the NMS presentations to the plurality of remote devices  215 -n. It will be appreciated that, at the frequencies of the NMS presentations, splitters  266  and  267  provide low insertion loss between port  268  and the splitter  265 , thereby ensuring the NMS presentations are routed to the plurality of remote devices  215 -n. Additionally, in an active SIM  210 , the amplifier  275  further prevents the NMS presentations from reaching the CN  130 . 
     Moreover, diplex filters  250  and  270  provide a path for upstream signals from the primary STT  205  to the headend. Similarly, diplex filters  260  and  270  provide a path for upstream signals from the plurality of remote devices  215 -n to the headend. A high pass filter  271  allows any upstream signals (e.g., signals ranging from 5 MHz to 45 MHz) to pass through to the diplex filter  270  on to the CN  130 . It will be appreciated that the reverse signals intended to remain in the NMS  200 , such as reverse command signals from the remote devices  215 -n, are reflected back and routed to the primary STT  205 . Furthermore, the SIM  210  receives the downstream broadband signals from the headend  110  at diplex filter  270 , which provides the downstream signals to the primary STT  205  or, alternatively, to both the primary STT  205  and the plurality of remote devices  215 -n. 
       FIG. 9  illustrates a block diagram of a second embodiment of a SIM  210  comprising passive splitter/isolation components in accordance with the present invention. More specifically, the NMS presentations from the primary STT  205  are provided to SIM  210  via port  268 . A band reject filter (BRF)  910  rejects the frequencies of the selected NMS presentations (e.g., from 852 MHz to 858 MHz), thereby not allowing the presentations to leave the network  200 . It will be appreciated that the NMS presentations are reflected off the BRF  910  and routed to the splitter  265  for transmission to the plurality of remote devices  215 -n. It will be appreciated that there is a high insertion loss between a SIM port  269 -n and the primary STT input port  268  at all other frequencies. A high pass filter (HPF)  915  is included to ensure that the reverse command signals provided by the plurality of remote devices  215 -n are reflected and routed to the primary STT  205  and not transmitted to the CN  130 . 
     Notably, the preferred embodiments of the SIM  210  provide protection against any of the reverse command signals from leaving the NMS  200 , thereby ensuring proper delivery to the primary STT  205  while also avoiding any interference with separate networked multimedia systems that may be in close proximity. A further advantage is that the SIM  210  enhances privacy and security by making the NMS  200  unobservable to any upstream devices in the CN  130 . 
     A Preferred Embodiment of a Remote Device  215 -n 
       FIG. 5  is a simplified diagram of one preferred embodiment of a remote STT device  215 -n. It will be appreciated that the remote devices  215 -n may be identical to the primary STT  205  and just share the storage device contents of the primary STT  205 . Alternatively, the remote devices  215 -n may be a simplified or conventional version of the primary STT  205 . A processor  305  and a tuner system  335 , which may be a simplified processor and only one tuner, may be included to extract channels from the received downstream broadband signals. Additionally, decryptors and decoders (not shown) may be included to decode encoded signals for proper processing and display. Furthermore, the remote devices  215 -n may or may not include memory. Preferably, the remote devices  215 -n include a user input receiver  368 , such as an IR receiver or an RF receiver, that receives signals from a remote control, such as an IR remote control or an RF remote control. It will be appreciated that the remote control  505  is not required, and any user input device could be incorporated in the remote devices  215 -n. 
     As mentioned, the reverse command signals, which typically originate from user input signals (e.g., tuned channels, NMS functions, or IPG display) or generated administrative signals (e.g., turn-on signals), could be processed using various methods depending upon the type of remote control used. By way of example, if an RF remote control is used, the RF signals could be modulated to a desired frequency that does not interfere with any downstream or upstream signals that are transmitted via the common coaxial cable  221 -n. There may be, however, RF interference issues between the remote control and other RF devices in the area. Alternatively, if an IR remote control device is used, RF interference is not an issue. The IR signals do, however, require modulation with a carrier frequency and subsequently multiplexed onto the coaxial cable  221 -n. Accordingly, this will prevent the requirement of running separate reverse command transmission media to accommodate the serial data streams, such as twisted pair cable, from each remote device  215 -n to the SIM  210 . It will be appreciated that if the user input signals indicate non-NMS signals, for example, a channel change or volume change, the remote device  215 -n processes and performs the operation internally. In other words, these types of user input signals are not routed throughout the NMS  200 . 
     Notably, in accordance with the present invention, the reverse command signals are transmitted via the coaxial cable  221 -n that is routed between each remote device  215 -n and the SIM  210 . A preferred embodiment of the present invention processes and transmits the reverse command signals that are indicative of user input commands using frequency shift keying (FSK) and utilizes existing components that are typically included in a conventional remote set-top terminal. As mentioned, a QPSK modulator is typically included in the upstream transmitter  350  for modulating conventional upstream signals, which are signals ranging from 5 MHz to 40 MHz, for transmission to the headend and, in accordance with the present invention, for modulating the reverse command signals that are routed throughout the NMS  200 . Preferably, the existing QPSK modulator modulates the reverse command signals to an FSK signal at a frequency that is below the conventional upstream signals (i.e., below 5 MHz). In this manner, the reverse command signals do not interfere with conventionally transmitted upstream signals that may be provided from the remote devices  215 -n. 
       FIG. 6  is a block diagram illustrating one preferred embodiment of a QPSK transmitter  600  that converts user input command signals into FSK signals for transmission to the SIM  210 . The user input command signals, such as a channel change, request for an IPG display, request for a stored presentation, etc., are presented from the user input receiver  368  to the QPSK transmitter  600  as serial data. In conventional QPSK transmitters, the input serial data is converted to parallel signals (A, B), and the parallel signals are subsequently mapped directly to a phase change A(p by a differential encoder. An example is shown in Table 1. 
                                 TABLE 1                       Input Serial               Data               A B   Δφ                          0 0   0           0 1   +π/2           1 0   −π/2           1 1   π                        
The output of the conventional QPSK transmitter is, therefore, a QPSK modulated output signal. Disadvantageously, however, the receiving equipment, such as would be required in the primary STT  205 , is complex and expensive. On the other hand, the present invention includes a precoder  605  that precodes the input serial data to generate a frequency shift keyed signal, thereby requiring a less complex, inexpensive receiver in the primary STT  205 .
 
     In accordance with the present invention, the precoder  605  operates on the input serial data to produce, for example,  2  symbols for each input bit. By way of example, the input serial data, x(n), may be changed to output serial data, x′(n), as follows:
 
when  x ( n )=1:  x′ ( n )=[01 01]; and
 
when  x ( n )=0:  x′ ( n )=[10 10],
 
where the sample time of the input x is, in this example, 4 times that of the output x′. For x(n)=1, therefore, the precoder  605  generates two symbols with each symbol producing a phase change of +π/2 (as shown in Table 1), and a total phase change of π. Similarly, for x(n) = 0 , the precoder  605  generates two symbols with each symbol producing a phase change of −π/2, and a total phase change of −π. It will be appreciated that the output serial data, x′(n), may be any arbitrary number of symbols, such as four symbols for an input bit, and the phase changes may be different than shown in Table 1 so long as the change is significant enough that the FSK demodulator in the command receiver  285  in the primary STT  205  can detect the change in frequency. Additionally, the precoder  605  does not have to be a dedicated piece of hardware; the precoder  605  can be used elsewhere within the remote terminal  215 -n. Furthermore, the precoder  605  can be, for example, a look-up table that is stored in memory, or it can be hardware, such as logic gates. The precoded signals are provided to a serial-to-parallel (S/P) converter  610  for providing parallel signals (A, B). A differential encoder  615  receives the A and B bits and encodes them according to the phase changes shown in the example Table 1 to provide mapped I and Q bits. An optional filter  620  may be used to shape the I/Q pulse. A carrier frequency is modulated by the I and Q bits via a QPSK modulator  625  to provide the FSK output signals at a desired frequency, such as, for example, in the range from 2 MHz to 4.5 MHz.
 
     It will be appreciated that the QPSK transmitter  600  may be enabled only when there are reverse command signals being transmitted, thereby enabling a way of preventing collisions between remote devices  215 -n. Further embodiments of collision avoidance will be discussed further below. Additionally, the remote command signals may be encrypted and, therefore, decrypted accordingly in the command receiver  285 . Further information regarding encryption/decryption can be found in copending U.S. patent application Ser. No. 10/154,495, which was filed on May 24, 2002 and is assigned to a common assignee, the teachings of which are hereby incorporated by reference. 
       FIG. 7  illustrates generation of an FSK signal for input serial data x(n)=[10010]. Graph  7 ( a ) illustrates the phase vs. the time over the duration of each symbol, which is shown to be linear, however, this is not required. As per the previous example, x(1)=[01 01], which corresponds to a total phase change of +π. The next input serial bit, x(0), is converted to [10 10], which corresponds to a total phase change of −π. Similarly, the next input serial bit, x(0), corresponds to a total phase change of −π, and so forth. As can be seen, graph  7 ( b ) illustrates a single positive value when x(n)=1, and a single negative value when x(n)=0. This constitutes the FSK signal. Note that, since the phase of the signal is continuous, the FSK signal generated may be designated as a continuous-phase FSK signal (CPFSK). It will be appreciated that there are further embodiments of an FSK transmitter. By way of example, an FSK transmitter could include a direct digital frequency synthesizer with two selectable frequency words. 
       FIG. 8  illustrates a second embodiment of the present invention for transmitting reverse command signals as OOK signals over the coaxial cable  221 -n to the SIM  210 . An on-off keying (OOK) inserter device  805  is either internally or externally added to the conventional remote device  215  for producing a modulated serial data stream that is suitable for transmission over coaxial cable. A logic gate  810  receives the serial data stream, which is indicative of the user input command signals, and an oscillator  815  provides an oscillated input signal at a specified frequency, such as 2 MHz. The logic gate  810  essentially gates the serial data stream to provide a modulated signal according to the user input signals for transmission over the coaxial cable  221 -n. 
     Referring again to  FIG. 2 , the reverse command signals from each of the plurality of remote devices  215 -n are provided to the primary STT  205  via the diplex filters  260 ,  250  in the SIM  210 . The remote device command receiver  285  receives the reverse command signals and instructs the primary STT  205  to provide return NMS presentations accordingly. A preferred embodiment of the command receiver  285  includes an FSK demodulator. It will be appreciated, however, that the receiver  285  can include any demodulator that is in accordance with the reverse command signal transmission technique. 
     After processing, the command receiver  285  sends signals indicative of the reverse command signal to the processor  305 . By way of example, if a remote device  215 -n requests the latest IPG or a list of the stored presentations, the processor  305  accesses the IPG display or the list via the navigational interface  322 , which subsequently forwards the IPG or the list to the requesting remote device  215 -n. The remote device  215 -n may then, upon user input, select a presentation from the IPG or the stored presentations. For example, upon receipt of the reverse command signals indicative of a selected stored presentation, the processor  305  extracts the selected presentation from the storage device  330  and transmits the presentation to the remote device  215 -n via the modulator  240 . The remote device  215 -n tunes to the modulator frequency and waits for the response (i.e., the stored presentation). Notably, in accordance with the present invention a remote device  215 -n that views a stored presentation is capable of utilizing advanced features via the primary STT  205 , such as play, pause, fast-forward, or rewind functions, with the selected presentation. More specifically, a remote device  215 -n receives user input indicating one of the play, pause, fast-forward, or rewind signals and forwards the reverse command signals indicative of the user input signals to the primary STT  205 . The processor  305  subsequently performs the function relating to the user input signals on the stored presentation that is being viewed, such as, for example, pausing transmission of the stored presentation until further commands are received. 
     A further example is a remote device  215 -n that requests a video-on-demand (VOD) presentation from a headend server via the primary STT  205 . It will be appreciated that if the remote device  215 -n is a broadcast-only device, it is incapable of transmitting upstream signals to the headend. In this case and in accordance with the present invention, the broadcast-only device  215 -n may transmit reverse command signals to the primary STT  205 , which acts as a gateway device. Subsequent to processing the command signals, the primary STT  205  may transmit upstream signals that are indicative of the command signals to the headend server. For instance, the remote device  215 -n selects a presentation from a displayed VOD list and transmits the reverse command signals to the primary STT  205 . The primary STT  205  processes the signals and subsequently transmits upstream signals to the headend server requesting the particular VOD presentation. The VOD presentation is then transmitted along with the downstream signals to the primary STT  205 , which may optionally store the presentation on the storage device  330 , and, either concurrently or subsequently, forward the VOD presentation to the requesting broadcast-only remote device  215 -n. Alternatively, the requesting remote device  215 -n can extract the VOD presentation with an included tuner from the downstream signals using, for example, a predetermined channel frequency or other identifying convention. 
     Collision avoidance between the remote devices  215 -n can be significantly improved in several ways. A preferred embodiment of the present invention, however, utilizes the asynchronous input data bits as an inexpensive way to transmit the reverse command signals from the plurality of remote devices  215 -n to the primary STT  205 . More specifically, the user input data is a sequence of asynchronous characters called a cell. Each cell contains a preamble, which is followed by several characters. The characters include, for example,one start bit, eight data bits, and one stop bit. An example may be that a low logical level represents a start bit or a data bit  0 ; a high logical level represents a stop bit or data bit  1 . The eight data bits are the reverse command signals. After modulation by the QPSK transmitter  600 , the FSK asynchronous signals are provided to the primary STT  205 . A demodulator (not shown) included in the command receiver  285  demodulates the signals and provides the demodulated signals to a universal asynchronous receiver/transmitter (UART) (not shown) for framing into data bytes using the asynchronous characters. Advantageously, by using the asynchronous data, the command receiver  285  does not need time to synchronize with a remote device&#39;s reference clock. It will be appreciated that other collision avoidance and collision recovery methods exist and can replace or further enhance the above-described embodiment of the present invention. These methods are known to one skilled in the art. 
     It should be emphasized that the above-described embodiments of the invention are merely possible examples, among others, of the implementations, setting forth a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without departing substantially from the principles of the invention. All such modifications and variations are intended to be included herein within the scope of the disclosure and invention and protected by the following claims. In addition, the scope of the invention includes embodying the functionality of the preferred embodiments of the invention in logic embodied in hardware and/or software-configured mediums.