Abstract:
Systems and methods for wireless transmission of uncompressed HDTV signals are disclosed. In one embodiment, a method for transmitting an uncompressed HDTV signal over a wireless RF link, comprises providing a stream of regenerated data from the uncompressed HDTV signal; providing a first clock signal synchronized to said stream of regenerated data; encoding said stream of regenerated data, producing a stream of encoded data; providing a second clock signal synchronized to said stream of encoded data; demultiplexing said stream of encoded data, using said second clock signal, into an I data stream and a Q data stream; modulating a carrier with said I data stream and said Q data stream; and transmitting said carrier in a signal over the wireless RF link.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This patent application is a continuation of, commonly-owned U.S. patent application Ser. No. 10/406,931 entitled “Wireless RF Link for Uncompressed Transmission of HDTV Signals” filed on Apr. 3, 2003, (now U.S. Pat. No. 7,139,319) which application is incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The present invention generally relates to wireless radio frequency (RF) systems for RF transmission and reception of high definition television (HDTV) signals and, more particularly, to systems and methods for wireless transmission of uncompressed HDTV signals. 
   BACKGROUND OF THE INVENTION 
   Common approaches for RF transmission of HDTV signals digitally compress the HDTV signal to address problems due to bandwidth and modulation limitations. For example, uncompressed transmission of HDTV signals occurs at a data rate of 1.485 giga-bits per second (Gbps), a data rate that is too high to be accommodated by conventional, low-bandwidth RF transmission. Digital compression reduces the data rate so that conventional, low-bandwidth RF transmission can be used. The resulting HDTV signal may be decompressed at the destination or receiving end of the RF link. The signal compression and decompression can generate artifacts that degrade the signal quality, and begin to negate the high picture quality specified by HDTV. In addition, latency generated by compression/decompression, i.e., the time delay between generation of the uncompressed HDTV signal and reception of the decompressed HDTV signal after compression and decompression, creates a time delay unacceptable for live broadcast synchronization. 
   It can be impractical, however, to use current, lower bandwidth, wireless RF systems to transmit uncompressed HDTV signals because complex and costly modulation and coding schemes are required to achieve reasonable HDTV performance. The Society of Motion Pictures and Television Engineers (SMPTE) standard 292M defines the electrical characteristics of the high definition HDTV signal. SMPTE standards also define the acceptable transmission medium for HDTV. For example, fiber optic cable, coaxial cable, and RF wireless transmission are all acceptable transmission media for HDTV signals. 
   HDTV signal transmission, for example, at an event or filming site, using any of the current cable, fiber optic, or wireless RF transmission capabilities, is subject to a variety of shortcomings. For example, if fiber optic cables are used they usually must be pre-installed at the event or filming site. Cables generally require permits to be obtained in advance and the time and cost for installation of cables can impose constraints on televising the event or filming. Fiber optic cables can be aesthetically undesirable, frequently unsafe, and often logistically impossible. For example fiber optic cables are usually buried months in advance for some golf events, and television engineers complain that a major headache in covering stadium sports events is the problem of fans tripping over their cables. Wireless RF transmission typically suffers from the digital compression problems, as described above, due to the limited bandwidth available using conventional, low-bandwidth RF transmission. 
   Television studios are now in the process of converting all of their broadcast productions exclusively to HDTV. In order for a high definition RF camera system to provide the same functionality as standard definition (SD), it is necessary to use an uncompressed digital link. Using an uncompressed link eliminates delays introduced by compression encoding and decoding. Such delays are unacceptable because they introduce production difficulties. Although wireless RF transmission of uncompressed HDTV signals has been achieved, for example, at a recent Super Bowl event, the RF transmission of uncompressed HDTV signals has been accomplished using on/off keying modulation. On/off keying is an inefficient form of modulation which imposes several limitations, for example, limited range, and which requires employing extremely high frequency radio waves in the 71-76 gigahertz (GHz) range, also known as V band (40-75 GHz) and W band (75-110 GHz), in order to accommodate the high, 1.485 Gbps, data rate. 
   RF transmission at such extremely high frequencies, however, also entails a number of technical difficulties. Technical difficulties for extremely high frequency RF transmission may include, for example, distortion due to the bandwidth required for high data rate, providing adequate transmit power, limitations on range, and antenna design tradeoffs. Link designs must trade between distance, effective radiated power (ERP), bit error rate (BER) performance, forward error correction, link margin, and component availability to develop a usable system. These technical difficulties become more critical in a portable wireless RF transmission system. Using modulators and receivers capable of performing at the 1.485 Gbps rate, an HDTV signal from a source—such as an HDTV camera or recorder—could be transmitted uncompressed to the proper facility for production—such as a local studio facility. Portable systems for transmission of uncompressed HDTV signals over wireless RF links could allow a portable hand-held camera to move from location to location within the receiver range, making HDTV transmission of sporting events or electronic newsgathering in real time possible. The ability to connect real-time to studios for instant direction and editing could offer the prospect of greatly reduced cost and cycle time for content creation. 
   As can be seen, there is a need for transmitting and receiving uncompressed HDTV signals over a wireless RF link. Also there is a need for high bandwidth, wireless RF links allowing the transmission of HDTV digital signals at the full 1.485 Gbps rate, that can be realized in a portable system that provides a quick, easy set-up where one HDTV signal can be transmitted and received over each link. 
   SUMMARY OF THE INVENTION 
   In one aspect of the present invention, a method for transmitting and receiving an uncompressed HDTV signal over a wireless RF link includes providing a clock signal synchronized to the uncompressed HDTV signal; and providing a stream of regenerated data from the uncompressed HDTV signal, with the clock signal synchronized to the stream of regenerated data. The clock signal is then used for demultiplexing the stream of regenerated data into an I data stream and a Q data stream. The method further includes modulating a carrier with the I data and the Q data stream; transmitting the carrier over the wireless RF link; demodulating the carrier so that the I data stream and the Q data stream are recovered; multiplexing the I data stream and the Q data stream into a single stream of HDTV data; and recovering the uncompressed HDTV signal from the single stream of HDTV data. 
   In another aspect of the present invention, a method for transmitting an uncompressed HDTV signal over a wireless RF link includes: providing a stream of regenerated data from the uncompressed HDTV signal; providing a first clock signal synchronized to the stream of regenerated data; encoding the stream of regenerated data, producing a stream of encoded data; providing a second clock signal synchronized to the stream of encoded data; demultiplexing the stream of encoded data, using the second clock signal, into an I data stream and a Q data stream; modulating a carrier with the I data stream and the Q data stream; and transmitting the carrier over the wireless RF link. 
   In still another aspect of the present invention, a method for receiving an uncompressed HDTV signal over a wireless RF link includes steps of: receiving the carrier over the wireless RF link; demodulating the carrier so that the I data stream and the Q data stream are recovered; multiplexing the I data stream and the Q data stream into a single stream of HDTV data; and decoding the single stream of HDTV data so that the uncompressed HDTV signal is recovered. 
   In yet another aspect of the present invention, a method for transmitting and receiving an uncompressed HDTV signal over a wireless RF link includes steps of: providing a stream of regenerated data having a first data rate of 1.485 Gbps from the uncompressed HDTV signal; providing a first clock signal, using edge detection of the stream of regenerated data to generate the first clock signal, and synchronize it to the stream of regenerated data; encoding the stream of regenerated data using a forward error correction code, producing a stream of encoded data having a second data rate higher than the first data rate by a coding overhead of the forward error correction code; providing a second clock signal using edge detection of the stream of encoded data to generate the second clock signal synchronized to the stream of encoded data, the second clock signal having a rate higher than the first clock signal by the coding overhead; demultiplexing the stream of encoded data, using the second clock signal, into an I data stream and a Q data stream; and QPSK modulating an IF carrier with the I data stream and the Q data stream. 
   The method also includes steps of: up converting the IF carrier to an RF carrier; transmitting the RF carrier over the wireless RF link; receiving the RF carrier over the wireless RF link; down converting the RF carrier to an IF frequency signal having frequency greater than 1.5 GHz and less than 6 GHz; demodulating the IF frequency signal so that the I data stream and the Q data stream are recovered; generating a third clock signal from the I data stream and the Q data stream, the third clock signal synchronized to the I data stream and the Q data stream; multiplexing the I data stream and the Q data stream, using the third clock signal, into a single stream of HDTV data; and decoding the single stream of HDTV data, using the third clock signal, so that the uncompressed HDTV signal is recovered. 
   In a further aspect of the present invention, a method of providing a wireless RF link for an HDTV system includes steps of: performing data regeneration on an uncompressed HDTV signal that produces a stream of regenerated HDTV data; synchronizing a first clock signal to the stream of regenerated HDTV data; encoding the stream of regenerated HDTV data, producing a stream of encoded data; synchronizing a second clock signal to the stream of encoded data; demultiplexing the stream of encoded data, using the second clock signal, into an I data stream and a Q data stream; and modulating a carrier with the I data stream and the Q data stream. The method further includes steps of: transmitting the carrier over the wireless RF link; receiving the carrier over the wireless RF link; demodulating the carrier so that the I data stream and the Q data stream are recovered; generating a third clock signal from the I data stream and the Q data stream, the third clock signal being synchronized to the I data stream and the Q data stream; using the third clock signal to multiplex the I data stream and the Q data stream into a single stream of HDTV data; and decoding the single stream of HDTV data so that the uncompressed HDTV signal is recovered. 
   These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention are described in detail below with reference to the following drawings. 
       FIG. 1  is a system diagram showing an exemplary HDTV system using dual polarization (i.e. frequency re-use) to transmit two uncompressed HDTV signals over a single RF channel, according to an embodiment of the present invention; 
       FIG. 2  is a system diagram showing an exemplary HDTV system with a wireless RF link transmitting uncompressed HDTV signals, according to an embodiment of the present invention; 
       FIG. 3  is a block diagram illustrating transmission of uncompressed HDTV signals, according to an embodiment of the present invention; 
       FIG. 4  is a block diagram illustrating single-polarization reception of uncompressed HDTV signals, according to one embodiment of the present invention; 
       FIG. 5  is a block diagram illustrating dual polarization signal reception of uncompressed HDTV signals over a single channel, according to another embodiment of the present invention; and 
       FIG. 6  is a flow chart illustrating a method for transmitting and receiving uncompressed HDTV signals, in accordance with an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. 
   Broadly, embodiments of the present invention provide systems and methods for transmitting and receiving uncompressed high definition television (HDTV) signals over a wireless RF link. The HDTV digital signals may be generated, for example, from an HDTV camera, stored HDTV source or memory, or recorded images. One embodiment provides high bandwidth, wireless RF links allowing the transmission of HDTV digital signals at the full 1.485 giga-bit per second (Gbps) rate, according to the Society of Motion Pictures and Television Engineers (SMPTE) standard 292M, for a portable system where one HDTV signal can be transmitted and received over each link. One embodiment may incorporate high-speed modulation to achieve line of sight RF links up to 10 kilometers in range. Such high speed modulation is described in U.S. patent application Ser. No. 10/071,954, now U.S. Pat. No. 7,065,153 filed Feb. 6, 2002, titled “High Speed QPSK MMIC and QAM Modulator”, having assignee in common with the present invention, and incorporated herein by reference. One embodiment may also incorporate an apparatus for wireless RF transmission of uncompressed HDTV signals as described in now abandoned U.S. patent application Ser. No. 10/408,002, filed Apr. 3, 2003, having assignee in common with the present invention, and incorporated herein by reference. 
   HDTV systems as specified by SMPTE standard 292M are clockless systems, i.e., the HDTV signal is not accompanied by a synchronous clock. In one embodiment of the present invention, clock synchronization is provided to an HDTV signal so that efficient modulation schemes—such as QPSK and QAM—may be used to modulate the RF carrier with the HDTV data. Thus, the high data rate HDTV data at 1.485 Gbps may be efficiently modulated so that less bandwidth is required to transmit the signal over an RF link in accordance with an embodiment of the present invention. Therefore, in contrast to the prior art, RF links in accordance with an embodiment of the present invention may operate at a variety of frequency bands from 18 GHz up to 110 GHz. The RF links may be implemented as fixed or portable operation, and links may be one way (simplex) or full two-way (duplex). HDTV signals may be transmitted on the RF links from cameras or other HD sources to recorders, local studio facilities, or between studios for processing or distribution. 
   Referring now to  FIGS. 1 and 2 ,  FIG. 1  illustrates an exemplary HDTV system  100   a  according to one embodiment and  FIG. 2  illustrates an exemplary HDTV system  100   b  according to another embodiment. System  100   a  may include an RF channel  102   a . A dual polarization technique may be used with RF channel  102   a  to provide signal transmission via left-hand circular polarization (LHCP)  104  and right-hand circular polarization (RHCP)  106  for frequency re-use over a single channel. System  100   b  may include an RF channel  102   b . A single polarization or a conventional technique may be used with RF channel  102   b , allowing one signal to be transmitted over the RF channel  102   b.    
   System  100   a  may transmit an uncompressed HDTV signal  108   a  from source  110   a , which may be, for example, an HDTV camera as shown in  FIG. 1 . System  100   a  may transmit uncompressed HDTV signal  108   a  using transmitter  112   a  with the dual polarization technique to provide transmission via LHCP  104  over RF channel  102   a  to receiver  114   a . Similarly, system  100   a  may transmit an uncompressed HDTV signal  118   a  from source  120   a , which may be, for example, an HDTV tape source as shown in  FIG. 1 . System  100   a  may transmit uncompressed HDTV signal  118   a  using transmitter  122   a  with the dual polarization technique to provide transmission via RHCP  106  over RF channel  102   a  to receiver  114   a . HDTV signals  108   a  and  118   a  may conform to SMPTE standard 292M, and may have a data rate of 1.485 Gbps. 
   Receiver  114   a  may provide the received signal  124   a  corresponding to uncompressed HDTV signal  108   a  transmitted via LHCP  104 , using dual polarization technique, over RF channel  102   a  to demodulator  128   a . Similarly, receiver  114   a  may provide the received signal  126   a  corresponding to uncompressed HDTV signal  118   a  transmitted via RHCP  106 , using dual polarization technique, over RF channel  102   a  to demodulator  130   a . Demodulator  128   a  may provide an HDTV signal  132   a  to an HDTV device  136   a , which may be, for example, an HDTV monitor as shown in  FIG. 1 . Demodulator  130   a  may provide an HDTV signal  134   a  to an HDTV device  138   a , which may be, for example, an HDTV recorder as shown in  FIG. 1 . HDTV signals  132   a  and  134   a  may conform to Society of Motion Pictures and Television Engineers (SMPTE) standard 292M, and may have a data rate of 1.485 Gbps. HDTV signals  132   a  and  134   a  may be recovered, respectively, from HDTV signals  108   a  and  118   a.    
   Single channel system  100   b  is simpler but operates similarly to system  100   a . Thus, system  100   b  may transmit an uncompressed HDTV signal  108   b  from source  110   b , which may be, for example, an HDTV camera as shown in  FIG. 2 . System  100   b  may transmit uncompressed HDTV signal  108   b  using transmitter  112   b , using conventional or single polarization techniques, over the link  105  of RF channel  102   b  to receiver  114   b . HDTV signal  108   b  may conform to Society of Motion Pictures and Television Engineers (SMPTE) standard 292M, and may have a data rate of 1.485 Gbps. 
   Receiver  114   b  may provide the received signal  124   b  corresponding to uncompressed HDTV signal  108   b  received over link  105  of RF channel  102   b  to demodulator  128   b . Demodulator  128   b  may provide an HDTV signal  132   b  to an HDTV device  136   b , which may be, for example, an HDTV recorder as shown in  FIG. 2 . HDTV signal  132   b  may conform to Society of Motion Pictures and Television Engineers (SMPTE) standard 292M, and may have a data rate of 1.485 Gbps. HDTV signal  132   b  may be recovered from HDTV signal  108   b.    
   Referring now to  FIG. 3 , transmission system  200  illustrates RF transmission of an uncompressed HDTV signal  202 —such as signal  108   a  or  108   b  seen in FIGS.  1  and  2 —according to one embodiment. Uncompressed HDTV signal  202  may be equalized at module  204  to compensate for any cable distortions due to cable length or type that, for example, may cause signal  202  to not meet SMPTE 292M requirements. For example, equalization may be performed using commercially available equalization devices, as known in the art, so that equalized signal  206  meets the SMPTE 292M requirements. Data from equalized signal  206  may be regenerated at module  208  to provide regenerated data  210  so that a clock signal  214  synchronized to regenerated data  210  may be provided by clock  212 . For example, clock recovery at clock  212  may be provided by edge-detection of regenerated data  210 . Also, for example, clock recovery at clock  212  may be provided by passing regenerated data  210  through a squaring multiplier to generate a clock signal  214  synchronized to regenerated data  210 . 
   Regenerated data  210  and clock signal  214  may be used to perform forward error correction coding (FEC) at module  216  to improve link performance. For example, Reed-Solomon coding, interleaving coding, or turbo product codes (TPC), as known in the art, may be used. FEC coding at module  216  requires adding redundancy to the signal (i.e. coding overhead) by intentionally adding bits to correct errors at the receiver without having to communicate back and forth with the transmitter for additional information on which bits are in error. Depending on the type of code used this can entail a coding overhead due to the additional capacity, increasing the data rate. Thus, encoded data  218  may be provided at a higher data rate, for example, 1.607 Gbps, and clock signal  220  is provided at the higher rate to match the higher rate encoded data  218 , so that the rate of clock signal  220  is higher than the rate of clock signal  214  by the coding overhead. For example, a phase-locked loop (PLL) included in module  216  may be used to generate the higher rate clock signal  220  and synchronize clock signal  220  to encoded data  218 . 
   Clock signal  220  may be used as a timing source to demultiplex encoded data  218  into two data streams, an in-phase (I) data stream  224  and a quadrature (Q) data stream  226  at block  222  as shown in  FIG. 3 . The two synchronized data streams  224  and  226 , which contain the data of the original uncompressed HDTV signal  202 , may be used to provide efficient modulation of a carrier by the data of signal  202 . For example, the amplitude and offset of the voltages representing the data streams  224  and  226  may be adjusted as illustrated by block  228  and appropriate inputs  230  may be provided to a modulator  232 . Modulator  232  may be, for example, a quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) implementation on a monolithic microwave integrated circuits (MMIC) chip, as described above. For example, an oscillator (i.e. frequency source) may provide the center frequency at which modulator  232  operates, typically between 18 GHz and 23 GHz depending on frequency upconversion spur analysis, as known in the art. Modulator  232  output may be a QPSK waveform that may then be frequency upconverted at block  234  to an appropriate transmit frequency. The frequency translation at block  234  may combine a QPSK waveform with a converting oscillator to generate a desired transmit frequency. For example, the minimum required bandwidth necessary for a 1.485 Gbps QPSK waveform with error correction coding overhead may be approximately 900 MHz. The modulated carrier  238  may be broadcast by an antenna  236  over a wireless RF link—such as link  102   a  or  102   b , seen in  FIGS. 1 and 2 . 
   Referring now to  FIGS. 4 and 5 , reception system  300  shown in  FIG. 4 , illustrates RF reception, according to one embodiment, of an uncompressed HDTV signal—such as signal  108   a  or  108   b  seen in FIGS.  1  and  2 —that may be transmitted via a modulated carrier—such as modulated carrier  238 —that may be received by a receiving antenna  302 . The received uncompressed HDTV signal  304  may be passed to a low noise amplifier (LNA)  306 . 
   In an alternative embodiment, illustrated by reception system  301  in  FIG. 5 , uncompressed HDTV signal  304  may comprise an LHCP signal  304   a  and an RHCP signal  304   b —such as signals  108   a  and  118   a  sent over a single RF channel  102   a  using a dual polarization technique. The two signals, LHCP signal  304   a  and RHCP signal  304   b , may be separated by an ortho-mode transducer  305 , so that LHCP signal  304   a  may be passed to low noise amplifier (LNA)  306   a  and RHCP signal  304   b  may be passed to low noise amplifier (LNA)  306   b . The alternative embodiment shown in  FIG. 5  uses dual polarization to allow two transmitters to broadcast to a single receiver site. The two transmitters must operate on different polarizations, right-hand circular and left-hand circular, in order to take advantage of frequency reuse. The receive antenna utilizes an ortho-mode transducer  305  to separate the left and right polarization for low noise amplification, frequency down conversion, and data recovery. This method allows for transmitting two signals each from a different transmitter over the same frequency region. The single polarization down converter of the embodiment shown in  FIG. 4  may simplify the electronics for single channel use. 
   Referring again to  FIGS. 4 and 5 , the amplified signal  308  may be down converted at block  310  by multiplying amplified signal  308 , for example, using a multiplier  312  by the output of a local oscillator—such as local oscillator  314 —to produce a down converted intermediate frequency (IF) signal or carrier  316  at a lower frequency than that of signal  304 . For example, an IF between 1.5 GHz and 6 GHz may typically be chosen, so that a 2-GHz IF may be chosen to illustrate the present embodiment. In a practical implementation, for example, the functions of receiving antenna  302 , LNA  306 , and frequency down conversion of block  310  may be remotely located to provide optimum line-of-sight to a transmitter—such as transmitter  112   a  shown in  FIG. 1 . The correct local oscillator source—such as local oscillator  314 —may be combined with the incoming RF signal  308  to shift the signal  308  down to a 2 GHz IF carrier  316  at the output of block  310 . Since the transmit frequency may not be fixed there can be numerous values for the local oscillator  314  in order to achieve the 2 GHz for IF carrier  316 . A 2-GHz IF may be selected, for example, for simplification of routing. A 2-GHz IF may allow for significant distance between the receive antenna, which could be located on a crane or pole, and the baseband hardware, used to implement demodulation and decoding as further described below, located on the ground. A 2-GHz IF signal output can typically drive up to 100 feet of coaxial cable or be converted to an optical signal. 
   IF carrier  316  may be passed to demodulator  318  for recovery of the baseband digital signals corresponding to I data stream  224  and Q data stream  226 . Demodulator  318 , for example, may take a coherent carrier recovered from IF carrier  316  and mix the coherent carrier with the modulated IF carrier  316  to generate baseband I data stream  324  and Q data stream  326 . 
   Bit synchronization and clock recovery may be performed on I data stream  324  and Q data stream  326 , respectively, at blocks  328  and  330  to generate a clock  332  that is synchronized with I data stream  324  and Q data stream  326 . Clock  332  may provide clock signal  334 , providing a timing source for the 2:1 multiplexing at block  336  multiplexing I data stream  324  and Q data stream  326  to obtain a single stream of encoded HDTV data  338  corresponding to encoded data  218 . Single stream of HDTV data  338  may be provided at a rate of 1.485 Gbps plus coding overhead. For example, the data rate with coding overhead given in the example above for encoded data  218  was 1.607 Gbps and, following that example, the data rate of single stream of HDTV data  338  may also be 1.607 Gbps. The encoded HDTV signal, i.e., HDTV data  338 , may be supplied a timing source from clock signal  334 , for example, at block  340 , for decoding single stream of encoded HDTV data  338  to generate the error corrected 1.485 Gbps HDTV signal  342 . 
   The logic levels of error corrected HDTV signal  342  may be shifted, for example, at block  344  after decoding to provide appropriate logic levels for adapting HDTV signal  342  to drive an electrical interface  346  or electrical to optical conversion may be performed at block  348  to drive optical interface  350 . 
   Referring now to  FIG. 6 , an exemplary embodiment of a method  400  for transmitting and receiving an uncompressed HDTV signal—such as signal  108   a  or  108   b  seen in FIGS.  1  and  2 —is illustrated in flowchart form. Exemplary method  400  may include blocks  402 ,  404 ,  406 ,  408 ,  410 ,  412 ,  414 , and  416 , which conceptually delineate method  400  for purposes of conveniently illustrating method  400  according to one embodiment. Exemplary method  400  is illustrated with reference to  FIGS. 3 ,  4  and  5 . 
   Method  400  may begin at block  402 , in which a clock signal may be synchronized to an HDTV signal. For example, data regeneration of equalized HDTV signal  206 , or HDTV signal  108   a  or  108   b , may be used with edge detection to provide synchronized clock signal  214 . 
   Method  400  may continue with block  404 , in which a synchronized clock signal may be used as a timing source for an encoder to encode the HDTV signal into an encoded data stream. For example, forward error correction coding—such as Reed-Solomon coding or turbo product coding—may be performed, in which synchronized clock signal  214  may be used as a timing source for the encoder to provide a stream of encoded data  218  from HDTV signal  206 . A higher rate clock signal  220  may be generated from encoder block  216  using a PLL, in which higher clock rate signal  220  may be synchronized to the higher rate stream of encoded data  218 . 
   Method  400  may continue with block  406 , in which the encoded HDTV data stream may be demultiplexed into I and Q data streams. For example, higher rate synchronized clock signal  220  may enable demultiplexing of stream of encoded data  218  into I data stream  224  and Q data stream  226 . 
   Method  400  may continue with block  408 , in which an RF carrier may be efficiently modulated by the HDTV data stream. For example, an RF carrier may be QPSK modulated by I data stream  224  and Q data stream  226  to provide modulated carrier  238 . Other types of efficient modulation may also be used, for example, 16 QAM or other higher orders of modulation. 
   Method  400  may continue with block  410 , in which the HDTV data stream may be transmitted over a wireless RF link. For example, modulated carrier  238  may be transmitted from a transmit antenna  236  to a receiving antenna  302 . 
   Method  400  may continue with block  412 , in which an HDTV data stream may be demodulated from a carrier to recover I and Q data streams. For example, an IF carrier  316  may be demodulated to recover an I data stream  324  and a Q data stream  326 . 
   Method  400  may continue with block  414 , in which I and Q data streams may be multiplexed into a single encoded HDTV data stream. For example, I data stream  324  and Q data stream  326  may be multiplexed into a single stream of encoded HDTV data  338 , which effectively recovers the transmitted encoded data  218 . I data stream  324  and Q data stream  326  may be multiplexed with the aid of a clock signal  334  generated by clock data recovery using edge detection, for example, from I data stream  324  and Q data stream  326 . 
   Method  400  may continue with block  416 , in which HDTV data stream may be decoded into an error corrected HDTV signal—such as HDTV signal  342 , meeting the SMPTE 292M standard—that effectively recovers the original HDTV signal—such as signal  108   a  or  108   b.    
   While preferred and alternate embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of these preferred and alternate embodiments. Instead, the invention should be determined entirely by reference to the claims that follow.