PATENT DOCUMENT

Publication Number: US-8249184-B2
Application Number: US-201113183112-A
Country: US
Kind Code: B2

Title: Content differentiated hierarchical modulation used in radio frequency communications

Abstract:
The present invention employs hierarchical modulation to simultaneously transmit data over different modulation layers using a carrier RF signal. Each modulation layer may be of a higher or lower order than the other modulation layers. Certain embodiments of the present invention may transmit different information on the different modulation layers. Other embodiments of the present invention may use the different layers for processing different information streams.

Claims:
1. A communication system comprising at least one base station, the at least one base station comprising transmit circuitry operable to:
 transmit first data using a first modulation layer of a first carrier radio frequency (RF) signal; 
 transmit second data using a second modulation layer of the first carrier RF signal during transmission of the first data; and 
 wherein the first and second modulation layers are hierarchical modulation layers of the carrier RF signal, and the first data comprises different content than the second data. 
 
     
     
       2. The system of  claim 1 , wherein the first data comprises data unrelated to the second data. 
     
     
       3. The system of  claim 1 , wherein the first data comprises a different type of media content than the second data. 
     
     
       4. The system of  claim 1 , wherein the first data comprises a different programming channel than the second data. 
     
     
       5. The system of  claim 1 , wherein the first data comprises a particular type of media content in a given program that is unrelated to the second data. 
     
     
       6. The system of  claim 5 , wherein the particular type of media content is one selected from a group consisting of audio content, video content, voice content, and specific data content. 
     
     
       7. The system of  claim 1 , wherein the first carrier RF signal comprises a plurality of modulation symbols, such that each of certain of the plurality of modulation symbols comprises first order bits that provide the first data and second order bits that provide the second data. 
     
     
       8. The system of  claim 7 , wherein the first order bits are of a higher order than the second order bits. 
     
     
       9. The system of  claim 7 , wherein the certain of the plurality of modulation symbols are quadrature amplitude modulation symbols, and the first order bits comprise phase information. 
     
     
       10. The system of  claim 1 , wherein the second modulation layer is time-shifted from the first modulation layer. 
     
     
       11. The system of  claim 10 , wherein a modulation rate of the first modulation layer is less than a modulation rate of the second modulation layer. 
     
     
       12. The system of  claim 1 , wherein the first data comprises first broadcast data and the second data comprises second broadcast data. 
     
     
       13. The system of  claim 1 , wherein the first data comprises first unicast data and the second data comprises second unicast data. 
     
     
       14. The system of  claim 1 , wherein the first data comprises broadcast data and the second data comprises unicast data. 
     
     
       15. The system of  claim 1 , wherein the first data comprises programming content. 
     
     
       16. The system of  claim 15 , wherein the programming content comprises content from at least one programming channel. 
     
     
       17. The system of  claim 15 , wherein the programming content is associated with at least one selected from a group consisting of audio content and video content. 
     
     
       18. The system of  claim 15 , wherein the second data comprises programming content. 
     
     
       19. The system of  claim 15 , wherein the second data comprises voice content. 
     
     
       20. The system of claim.  15  wherein the second data comprises specific data content. 
     
     
       21. The system of  claim 1 , wherein the first data comprises voice content. 
     
     
       22. The system of  claim 21 , wherein the second data comprises specific data content. 
     
     
       23. The system of  claim 21 , wherein the voice content is associated with a cellular telephone call. 
     
     
       24. The system of  claim 1 , wherein the first data comprises specific data content and the second data comprises specific data content. 
     
     
       25. The system of  claim 1 , further comprising another base station, the other base station comprising transmit circuitry operable to:
 transmit third data using a third modulation layer of a second carrier RF signal; 
 transmit the first data using a fourth modulation layer of the second carrier RF signal during transmission of the third data; and 
 wherein the third and fourth modulation layers are hierarchical modulation layers of the second carrier RF signal, and the first and third data are associated with different content. 
 
     
     
       26. The system of  claim 25 , wherein the first data is associated with content relating to a first geographic area and the second data is associated with content relating to a subset of the first geographic area. 
     
     
       27. The system of  claim 25 , wherein the first of the at least one base station is associated with transmitting to user equipment in a first geographic area and the second of the at least one base station is associated with transmitting to UE in a second geographic area. 
     
     
       28. The system of  claim 27 , wherein the first geographic area does not overlap with the second geographic area. 
     
     
       29. The system of  claim 1 , wherein the first data comprises broadcast data having national content and the second data comprises broadcast data having local content. 
     
     
       30. The system of  claim 1 , wherein the first data comprises broadcast data having regional content, and the second data comprises broadcast data having local content. 
     
     
       31. The system of  claim 1 , wherein the first data comprises at least one program channel for a basic program service and the second data comprises at least one program channel for a supplemental program service. 
     
     
       32. The system of  claim 1 , wherein the at least one base station forms a single frequency Network (SFN) by transmitting equivalent data on at least one equivalent modulation layer at the same time using a plurality of antennas. 
     
     
       33. The system of  claim 1 , wherein at least one of the first data and the second data is modulated onto at least one sub-carrier using one selected from a group consisting of orthogonal frequency division multiplexing (OFDM) and single-carrier frequency division multiplexing (SC-FDM). 
     
     
       34. The system of  claim 33 , wherein the first data is processed differently than the second data. 
     
     
       35. The system of  claim 1 , wherein the first of the at least one base station has a first antenna and a second antenna, wherein the first data is transmitted using the first and second antennas, and the second data is transmitted using only the first antenna. 
     
     
       36. The system of  claim 35 , wherein the first data is processed differently than the second data. 
     
     
       37. The system of  claim 35 , wherein the first data comprises content from at least one programming channel. 
     
     
       38. The system of  claim 1 , wherein at least one of the first data and second data comprises RF communications system control channel data. 
     
     
       39. The system of  claim 1 , further comprising at least one user equipment operable to receive the first carrier RF signal. 
     
     
       40. The system of  claim 1 , further comprising at least one relay station operable to receive the first carrier RF signal.

Description:
RELATED APPLICATIONS 
     This application is a Continuation of U.S. patent application Ser. No. 11/618,774, entitled CONTENT DIFFERENTIATED HIERARCHICAL MODULATION USED IN RADIO FREQUENCY COMMUNICATIONS, filed Dec. 30, 2006, which is related to U.S. patent application Ser. No. 11/942,492, entitled MODULATION DIVISION MULTIPLE ACCESS, filed Nov. 19, 2007, currently pending, and is also related to U.S. patent application Ser. No. 11/945,162, entitled PROCESSING DIFFERENTIATED HIERARCHICAL MODULATION USED IN RADIO FREQUENCY COMMUNICATIONS, filed Nov. 26, 2007, currently pending, the disclosures of which are incorporated herein by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to radio frequency (RF) transmitter modulation techniques used in RF communications systems. 
     BACKGROUND OF THE INVENTION 
     With each successive generation of RF communications systems, modulation techniques, access schemes, and communications protocols become more sophisticated and demanding. One universal goal is to increase the amount of information transmitted in a given communications band, and to accommodate different types of information that must be communicated. For example, first generation cellular networks were designed to provide only voice services; however, these networks have evolved to provide a number of simultaneous services, including internet traffic, such as emails, and provide multi-media services, such as broadcast and on demand services in specific geographic areas. Each of these services may have its own specific requirements for bandwidth, latency, acceptable error rate, and locations of availability. As a result, different processing methods have been developed, including orthogonal frequency division multiplexing (OFDM), single carrier frequency division multiplexing (SC-FDM), single frequency networks (SFN), multiple input multiple output (MIMO), and multi-hop and relayed transmissions. OFDM and SC-FDM can distribute a high bandwidth signal onto multiple sub-carriers of lower bandwidth. SFNs improve signal coverage of broadcast data by transmitting the same information at the same time from multiple antennas. MIMO adds antennas to a system to provide spatial multiplexing, diversity, or both. Multi-hop and relayed transmissions provide broadcast data to multiple base stations. Therefore, as communications systems evolve, there is a need to increase the number and diversity of services by improving how bandwidth is utilized. 
     SUMMARY OF THE INVENTION 
     The present invention employs hierarchical modulation to simultaneously transmit data over different modulation layers using a carrier RF signal. Each modulation layer may be of a higher or lower order than the other modulation layers. Certain embodiments of the present invention may transmit different information on the different modulation layers. Other embodiments of the present invention may use the different layers for processing different information streams. 
     Transmitting different information on different modulation layers may provide many useful applications. Unicast data is transmitted to a single user, whereas broadcast data is transmitted to multiple users. The present invention includes any combination of unicast data and broadcast data to be transmitted using any combination of the different modulation layers. Unicast data and broadcast data include different types of content, including audio content, video content, voice content, and specific data content. 
     Audio content may provide at least one channel of audio programming, which may provide an on demand audio program that is unicast to a single user, or distributed audio programs that are broadcast to multiple users. Similarly, video content may provide at least one channel of video programming. Voice content may include individual cellular telephone calls. Specific data content may include internet data, including emails, short messaging service messages, or downloaded information. The present invention includes any combination of types of content to be transmitted using any combination of the different modulation layers. 
     In the present invention, the different information on different modulation layers may be transmitted to different geographic areas. The content of the different information may be associated with different geographic areas. One example is a national news program may be broadcast to a large geographic area from multiple base stations using one modulation layer, and a local traffic program may be broadcast to a subset of the large geographic area from one base station using a different modulation layer. 
     The present invention may include using the different modulation layers in conjunction with other techniques for processing different information streams. One modulation layer may be used to provide broadcast data to multiple base stations that form a single frequency network (SFN). A SFN may be used to improve signal coverage of broadcast data by transmitting the same information at the same time from multiple antennas. 
     MIMO adds antennas to a system to provide spatial multiplexing, diversity, or both. The information transmitted from MIMO antennas may be provided from any combination of the different modulation layers. The additional MIMO antennas may be used to strengthen a SFN. One modulation layer may be used to provide broadcast data, which is transmitted from multiple MIMO antennas simultaneously. Another modulation layer may be used to provide multiple channels of data, which are transmitted from different MIMO antennas. 
     Video broadcast data may have high bandwidth requirements. OFDM or SC-FDM can distribute a high bandwidth signal onto multiple sub-carriers of lower bandwidth. The present invention may be used to provide different sub-carriers using different modulation layers, or to provide at least one sub-carrier using one modulation layer, and other information using at least one other modulation layer. 
     Multi-hop and relayed transmissions provide broadcast data or other system data to multiple base stations. The present invention may be used to provide any combination of system data, relayed data, and end user data using any combination of modulation layers. Certain modulation techniques may include one or more modulation layers that are compatible with modulation techniques that are used in existing communications networks. Therefore, the present invention may provide compatibility between different communications systems by using compatible modulation layers, which may allow an upgraded communications system to be backward compatible with legacy user equipment (UE). 
     Those skilled in the art will appreciate the scope of the present invention and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in association with the accompanying drawing figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the invention, and together with the description serve to explain the principles of the invention. 
         FIG. 1  shows an RF communications system. 
         FIG. 2A  shows a modulation symbol having 4 bits of information. 
         FIG. 2B  shows one embodiment of the present invention wherein the modulation symbol illustrated in  FIG. 2A  is divided into a lower modulation symbol and a higher modulation symbol. 
         FIG. 3  shows the present invention used with quadrature modulation. 
         FIG. 4  shows the four constellation points used in quadrature phase shift keying (QPSK) modulation, and their relationship with the lower modulation symbol. 
         FIG. 5  shows the 16 constellation points used in rectangular sixteen quadrature amplitude modulation (16-QAM), and their relationship with the lower modulation symbol. 
         FIG. 6  shows the 4 constellation points used in the first quadrant of 16-QAM. 
         FIG. 7A  shows the alignment of lower modulation layer data with higher modulation layer data in one embodiment of the present invention. 
         FIG. 7B  shows the lower modulation layer data time-shifted from the higher modulation layer data in an alternate embodiment of the present invention. 
         FIG. 8A  shows time multiplexed data included in the higher modulation layer data. 
         FIG. 8B  shows two single-frequency OFDM sub-carriers included in the higher modulation layer data. 
         FIG. 9  adds MIMO antennas to the base stations and some of the terminals illustrated in  FIG. 1 . 
         FIG. 10  shows single input single output (SISO) data included in the lower modulation layer data, and two MIMO sub-channels included in the higher modulation layer data. 
         FIG. 11  shows the present invention used with MIMO transmitter circuitry. 
         FIG. 12  shows details of the first base station illustrated in  FIG. 1 . 
         FIG. 13  is a block representation of a cellular communication system. 
         FIG. 14  is a block representation of a base station according to one embodiment of the present invention. 
         FIG. 15  is a block representation of a mobile terminal according to one embodiment of the present invention. 
         FIG. 16  is a logical breakdown of an OFDM transmitter architecture according to one embodiment of the present invention. 
         FIG. 17  is a logical breakdown of an OFDM receiver architecture according to one embodiment of the present invention. 
         FIG. 18  illustrates a pattern of sub-carriers for carrying pilot symbols in an OFDM environment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The embodiments set forth below represent the necessary information to enable those skilled in the art to practice the invention and illustrate the best mode of practicing the invention. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. 
     The present invention employs hierarchical modulation to simultaneously transmit data over different modulation layers using a carrier RF signal. Each modulation layer may be of a higher or lower order than the other modulation layers. Certain embodiments of the present invention may transmit different information on the different modulation layers. Other embodiments of the present invention may use the different layers for processing different information streams. 
     Transmitting different information on different modulation layers may provide, many useful applications. Unicast data is transmitted to a single user, whereas broadcast data is transmitted to multiple users. The present invention includes any combination of unicast data and broadcast data to be transmitted using any combination of the different modulation layers. Unicast data and broadcast data include different types of content, including audio content, video content, voice content, and specific data content. 
     Audio content may provide at least one channel of audio programming, which may provide an on demand audio program that is unicast to a single user, or distributed audio programs that are broadcast to multiple users. Similarly, video content may provide at least one channel of video programming. Voice content may include individual cellular telephone calls. Specific data content may include internet data, including emails, short messaging service messages, or downloaded information. The present invention includes any combination of types of content to be transmitted using any combination of the different modulation layers. 
     In the present invention, the different information on different modulation layers may be transmitted to different geographic areas. The content of the different information may be associated with different geographic areas. One example is a national news program may be broadcast to a large geographic area from multiple base stations using one modulation layer, and a local traffic program may be broadcast to a subset of the large geographic area from one base station using a different modulation layer. 
     The present invention may include using the different modulation layers in conjunction with other techniques for processing different information streams. One modulation layer may be used to provide broadcast data to multiple base stations that form a single frequency network (SFN). A SFN may be used to improve signal coverage of broadcast data by transmitting the same information at the same time from multiple antennas. 
     MIMO adds antennas to a system to provide spatial multiplexing, diversity, or both. The information transmitted from MIMO antennas may be provided from any combination of the different modulation layers. The additional MIMO antennas may be used to strengthen a SFN. One modulation layer may be used to provide broadcast data, which is transmitted from multiple MIMO antennas simultaneously. Another modulation layer may be used to provide multiple channels of data, which are transmitted from different MIMO antennas. 
     Video broadcast data may have high bandwidth requirements. OFDM or SC-FDM can distribute a high bandwidth signal onto multiple sub-carriers of lower bandwidth. The present invention may be used to provide different sub-carriers using different modulation layers, or to provide at least one sub-carrier using one modulation layer, and other information using at least one other modulation layer. 
     Multi-hop and relayed transmissions provide broadcast data or other system data to multiple base stations. The present invention may be used to provide any combination of system data, relayed data, and end user data using any combination of modulation layers. Certain modulation techniques may include one or more modulation layers that are compatible with modulation techniques that are used in existing communications networks. Therefore, the present invention may provide compatibility between different communications systems by using compatible modulation layers, which may allow an upgraded communications system to be backward compatible with legacy user equipment (UE). 
     The present invention may be used to simultaneously download information directly to user equipment (UE) and to transmit system information to system transceivers, such as repeaters, relays or base stations. The system information may include information for downloading by other system transceivers and synchronization information for broadcasting user information from multiple transceivers and antennas simultaneously. The present invention may provide compatibility between different communications systems having different modulation schemes, which may allow an upgraded communications system to be backward compatible with legacy UE. Additionally, low cost UE using the legacy modulation scheme could be feasible with such a system. For example, an upgraded system using multiple antennas, such as MIMO may be compatible with systems using single antennas, such as single input single output (SISO). A basic broadcast channel may be transmitted using one modulation layer from all of the MIMO antennas, and multiple supplemental broadcast channels may be transmitted using another modulation layer from different MIMO antennas. Legacy UE may receive the basic broadcast channel; however, upgraded UE is required to receive the supplemental broadcast channels. 
     Multiplexing is a processing technique for transmitting different streams of information using a common transmission entity. Frequency division multiplexing (FDM) transmits different streams of information using different frequencies. Time division multiplexing (TDM) interleaves different streams of information into a single combined information stream, which is then transmitted. Orthogonal frequency division multiplexing (OFDM) and single carrier frequency division multiplexing (SC-FDM) may combine FDM and TDM to create multiple sub-carriers for transmitting different streams of information. Other multiplexing techniques may be used with OFDM and SC-FDM to provide additional sub-carriers. Multiple input multiple output (MIMO) is a multiple antenna architecture, which may provide spatial multiplexing by allowing different information to be transmitted using different antennas. The present invention is associated with a new multiplexing technique called modulation division multiplexing (MDM), by transmitting different information on different modulation layers. MDM may be associated with a new multiple access technique called modulation division multiple access (MDMA). The present invention may be used with a single carrier RF signal, a multiple carrier RF signal, or both. Any frequency or bandwidth RF signal may be used with the present invention. 
     Existing user equipment may be able to receive and transmit only the lower modulation layer, and ignore the higher modulation layer. An upgraded system may be backward compatible with existing communications equipment using existing features, while adding additional features that may be supported with upgraded equipment. In one embodiment of the present invention, the hierarchical modulation method includes rectangular quadrature amplitude modulation (QAM), where lower layer modulation layer bits are encoded with only phase shifting, such as data used with quadrature phase shift keying (QPSK), and upper modulation layer bits are encoded with QAM; however, existing communications equipment may ignore the QAM data bits and receive only those bits encoded with quadrature phase shift keying. 
       FIG. 1  shows an RF communications system  10 , such as a cellular communications system, having a first base station  12  with a first antenna port ANT 1  coupled to a first base station antenna  14 , a second base station  16  with the first antenna port ANT 1  coupled to a second base station antenna  18 , a first mobile terminal  20  with the first antenna port ANT 1  coupled to a first mobile antenna  22 , a fixed terminal  24  with the first antenna port ANT 1  coupled to a fixed terminal antenna  26 , a second mobile terminal  28  with the first antenna port ANT 1  coupled to a second mobile antenna  30 , and a third mobile terminal  32  with the first antenna port ANT 1  coupled to a third mobile antenna  34 . The antennas  14 ,  18 ,  22 ,  26 ,  30 ,  34  transmit and receive radiated RF signals  36 . The base stations  12 ,  16  control information flow to and from the terminals  20 ,  24 ,  28 ,  32 , which ideally are controlled by whichever base station is the closest, presents the best quality RF link, or both. 
     The radiated RF signals  36  are modulated to encode digital information. A number of modulation and encoding techniques may be used, including frequency modulation (FM) with frequency shift keying (FSK), phase modulation (PM) with phase shift keying (PSK), amplitude modulation (AM) with amplitude shift keying (ASK), or any combination thereof. One common modulation technique in cellular communications systems is a combination of AM and PM, which is called quadrature amplitude modulation (QAM). One common modulation technique in early generations of cellular communications systems is quadrature phase shift keying (QPSK), which can encode 2 bits of information with each modulation symbol, or phase shift.  FIG. 2A  shows a modulation symbol  38  having 4 bits of information, including bit zero  40 , bit one  42 , bit two  44 , and bit three  46 . To encode 4 bits of information, 16 different possible modulation points are required for each modulation symbol  38 . 
       FIG. 2B  shows one embodiment of the present invention by dividing the modulation symbol  38  illustrated in  FIG. 2A  into a lower modulation symbol  48  and a higher modulation symbol  50 . The lower modulation symbol  48  includes bit two  44  and bit three  46 . The higher modulation symbol  50  includes bit zero  40  and bit one  42 . The lower and higher modulation symbols  48 ,  50  may encode information that is unrelated, that may be on different channels or sub-channels, or that may be differentiated in some manner. Other embodiments of the present invention may divide the modulation symbol  38  into more than two hierarchical modulation symbols, such as the lower modulation symbol  48 , the higher modulation symbol  50 , and at least one supplemental modulation symbol. 
       FIG. 3  shows one embodiment of the present invention used with quadrature modulation  52 , which is associated with phase modulation. Phase-shifts may be represented graphically on a two dimensional grid having an in-phase axis and a quadrature-phase axis. The two dimensional grid may be divided into four quadrants, including a first quadrant  54 , a second quadrant  56 , a third quadrant  58 , and a fourth quadrant  60 . If the four quadrants are used to represent four different possible modulation points, then two bits of information can be encoded, which could correspond with bits two and three  44 ,  46  of the lower modulation symbol  48 . The first quadrant  54  may be represented with bit two  44  equal to a zero and bit three  46  equal to a zero. The second quadrant  56  may be represented with bit two  44  equal to a one and bit three  46  equal to a zero. The third quadrant  58  may be represented with bit two  44  equal to a zero and bit three  46  equal to a one. The fourth quadrant  60  may be represented with bit two  44  equal to a one and bit three  46  equal to a one. 
       FIG. 4  shows the four constellation points used in quadrature phase shift keying (QPSK) modulation, and their relationship with the lower modulation symbol  48 , including bits two and three  44 ,  46 . The four constellation points include a first quadrant point  62 , a second quadrant point  64 , a third quadrant point  66 , and a fourth quadrant point  68 . The four constellation points used in QPSK have equal amplitudes and are differentiated only by phase; however, as long as the constellation points fall within the correct quadrant  34 ,  56 ,  58 ,  60 , the lower modulation symbol  48 , including bits two and three  44 ,  46  will be decoded correctly. This characteristic may be beneficial in mixing a system with phase and amplitude modulation, such as QAM, with a system having only phase modulation, such as QPSK. The QPSK system may be able to reliably receive and transmit the lower modulation symbol  48  in systems with QAM; therefore, upgraded communications equipment using QAM may be backward compatible with existing communications equipment using QPSK for certain features. In one embodiment of the present invention, a communications system may alternate between transmitting QAM signals and QPSK signals. Other embodiments of the present invention may use other combinations of FM, PM, and AM to provide hierarchical modulation systems. Some embodiments of such systems may be backward compatible. 
       FIG. 5  shows the 16 constellation points used in rectangular sixteen quadrature amplitude modulation (16-QAM), and their relationship with the lower modulation symbol  48 . With 16 different possible modulation points, then 4 bits of information can be encoded, which could correspond with bits two and three  44 ,  46  of the lower modulation symbol  48  and bits zero and one  40 ,  42  of the higher modulation symbol  50 . The sixteen constellation points include a first quadrant first higher point  70 , a first quadrant second higher point  72 , a first quadrant third higher point  74 , a first quadrant fourth higher point  76 , a second quadrant first higher point  78 , a second quadrant second higher point  80 , a second quadrant third higher point  82 , a second quadrant fourth higher point  84 , a third quadrant first higher point  86 , a third quadrant second higher point  88 , a third quadrant third higher point  90 , a third quadrant fourth higher point  92 , a fourth quadrant first higher point  94 , a fourth quadrant second higher point  96 , a fourth quadrant third higher point  98 , and a fourth quadrant fourth higher point  100 . 
       FIG. 6  shows the 4 constellation points used in the first quadrant  54  of 16-QAM, which include the first quadrant points  70 ,  72 ,  74 ,  76 . If the four first quadrant points  70 ,  72 ,  74 ,  76  are used to represent 4 different possible modulation points, then 2 bits of information can be encoded, which could correspond with bits zero and one  40 ,  42  of the higher modulation symbol  50 . The first quadrant first higher point  70  may be represented with bit zero  40  equal to a zero and bit one  42  equal to a zero. The first quadrant second higher point  72  may be represented with bit zero  40  equal to a one and bit one  42  equal to a zero. The first quadrant third higher point  74  may be represented with bit zero  40  equal to a zero and bit one  42  equal to a one. The first quadrant fourth higher point  76  may be represented with bit zero  40  equal to a one and bit one  42  equal to a one. In one embodiment of the present invention, the phases and amplitudes separating the first quadrant points  70 ,  72 ,  74 ,  76  from each other may be less than the phases and amplitudes separating the groups of first quadrant points  70 ,  72 ,  74 ,  76 , second quadrant points  78 ,  80 ,  82 ,  84 , third quadrant points  86 ,  88 ,  90 ,  92 , and fourth quadrant points  94 ,  96 ,  98 ,  100  from each other; therefore, the reliability of data provided with the lower modulation symbol  48 , called lower modulation layer data, may be greater than that provided for the higher modulation symbol  50 , called higher modulation layer data, particularly with wireless communications links with low signal margins. In wireless communications links that operate with high signal margins most of the time, the difference in the reliabilities may be indetectable; however, the reliabilities over time, called average reliabilities will show differences due to those situations that may occasionally produce low signal margins. 
     Broadcast data is data that is intended to be received by more than one end user. Another frequently encountered term in communications is multicast. The only difference between broadcast data and multicast data is that broadcast data is intended for more end users than multicast data; however, since there is no accepted dividing line between multicast data and broadcast data, in this specification the term broadcast should be taken to mean broadcast, multicast, or both. Broadcast data may be audio, video, or both. Examples of broadcast data include video programs and audio programs. Broadcast data with national content may include network programs such as national newscasts or movies. Broadcast data with regional content may include regional newscasts or statewide information programs. Broadcast data with local content may include weather or traffic information. Broadcast data with basic content may include network channels or news channels. Broadcast data with supplemental content may include special interest channels, such as a sports channel or an educational channel. Unicast data is data that is intended to be received by one end user. Examples of unicast data include voice unicast data, such as cellular phone calls, specific unicast data, such as email messages, short message services, audio unicast data, such as an on-demand audio program, and video unicast data, such as an on-demand video program. 
     Broadcast data or unicast data may be transmitted using channels or sub-channels. A channel is a flow of information that contains all of the information associated with an information group, such as a video program together with its associated audio channels and sub-titles. Sub-channels are used to divide a channel into multiple flows of information for transmission over some medium, such as a cellular network. The information group is reconstructed by combining the sub-channels. Sub-channels are commonly used when communications channels in a communications system have inadequate bandwidth to handle the full bandwidth of the information being transmitted. 
     The present invention includes processing different information streams using different modulation layers. OFDM is a technique for distributing data over a number of OFDM sub-carriers, which can be created by a number of different methods, so long as each sub-carrier is orthogonal with respect to other sub-carriers. In this context, orthogonal means each sub-carrier does not interfere with the other sub-carriers. The OFDM data can be provided by using carriers at different frequencies, which is known as frequency division multiplexing (FDM) associated with frequency division multiple access (FDMA), time multiplexing, which is known as time division multiplexing (TDM) associated with time division multiple access (TDMA), spatial multiplexing, which is a associated with multiple input multiple output (MIMO) systems that have multiple antennas such that each antenna may have different information, or any combination thereof. The present invention includes dividing modulation symbols, called modulation division multiplexing (MDM) associated with a new access technique called modulation division multiple access (MDMA). Related to OFDM is single carrier frequency division multiplexing (SC-FDM). The present invention may be used to provide one or more sub-carriers in an OFDM or SC-FDM system. Additionally, the present invention may be used with numerous multiplexing techniques, including FDM, TOM, special multiplexing, MDM, OFDM, SC-FDM, or any combination thereof. 
     In one embodiment of the present invention, the modulation symbols  48 ,  50  may include different types of information selected from the following group, including video broadcast channels, video broadcast sub-channels, video unicast channels, video unicast sub-channels, audio broadcast channels, audio broadcast sub-channels, audio unicast channels, audio unicast sub-channels, voice unicast data, specific unicast data, OFDM data, and OFDM sub-carriers. Other embodiments of the present invention may include more than two different modulation layers. 
     In one embodiment of the present invention, the lower modulation symbol  48  includes broadcast data having national content, and the higher modulation symbol  50  includes broadcast data having local content. In an alternate embodiment of the present invention, the lower modulation symbol  48  includes broadcast data having basic content, and the higher modulation symbol  50  includes broadcast data having supplemental content. In an additional embodiment of the present invention, the lower modulation symbol  48  includes information intended to be directly received by user equipment (UE). The higher modulation symbol  50  includes information intended to be received by a relay station for forwarding to other relay stations, UE, or both. A base station may serve as a relay station. A synchronization signal may be included to synchronize transmissions to UE from multiple base stations or relay stations. The information included in the lower modulation symbol  48  may be repeated in the higher modulation symbol  50 . The synchronization signal may include a preamble to facilitate synchronization. 
     The present invention includes processing different information streams using different modulation layers. Such processing may include providing a single frequency network (SFN). An SFN may be formed when multiple antennas in an RF communications system  10  transmit the same information on the same modulation layer at the same time, which provides robust data transmission since the multiple signals may fill in coverage holes caused by shadowing and multi-path effects; therefore, higher broadcast data rates may be feasible with SFN. SFN data may be included in the lower modulation symbol  48 , the higher modulation symbol  50 , or both. Some or all of the broadcast data that incorporates the present invention may include SFN data. 
     The present invention employs hierarchical modulation to simultaneously transmit information on different modulation layers using a carrier RF signal. In one embodiment of the present invention, first data to be transmitted is assigned to a first modulation layer and second data is assigned to a second modulation layer based on reliability criteria. The first and second modulation layers are hierarchical modulation layers of the carrier RF signal. Once assigned, the first data is transmitted using the first modulation layer of the carrier RF signal and the second data is transmitted using the second modulation layer of the carrier RF signal. One modulation layer is generally a higher order than the other modulation layer. 
     In one embodiment of the present invention, all things being equal, the lower order modulation layer is generally less reliable than the higher order modulation layer. In general, the reliability criteria takes the reliability characteristics of the different modulation layers into account when assigning the first and second data to the different modulation layers. For example, reliability information may be derived from signal strength measurements or channel conditions to determine an appropriate modulation to use for transmitting certain data. Alternatively, different data may be associated with different priorities in general as well as different transmission priorities. Entertainment channels may have a lower priority than emergency service channels. Although maintaining data integrity is important for file transfers, the relative transmission priority for a file transfer is generally much lower than that for voice or other streaming media. In essence, the reliability criteria may relate to the communication channels, the data being transmitted, the transmission of the data, any combination thereof or the like. For the various data, the reliability information is used to assign the various data to the different modulation layers for transmission. 
     In certain embodiments of the present invention, different data is broadcast to multiple users using different modulation layers. The different data is assigned to specific modulation layers based on reliability criteria. In one embodiment of the present invention, a single program is broken into two different data streams. One provides basic resolution content while the other provides optional higher resolution content. Upon receipt of the lower resolution content, only the lower resolution version of the program is available. If the higher resolution content is available, the lower and higher resolution versions of the program are combined to form a composite program of high resolution. With the present invention, the higher resolution content is transmitted using the lower order modulation layers and the lower resolution content is transmitted using the higher order modulation layers. 
     In voice applications, each modulation layer may support one or more voice calls. As such, the reliability criteria is used when assigning data for different voice calls to the different modulation layers. Some calls are supported on higher order modulation layers while others are supported on lower order modulation layers in light of the reliability criteria. 
     In one embodiment of the present invention, the base stations  12 ,  16  both transmit required broadcast data using the modulation layer with greater reliability, and transmit optional broadcast data using the modulation symbol with lesser reliability. In an alternate embodiment of the present invention, the base stations  12 ,  16  both transmit either national or regional data using the modulation layer with greater reliability, wherein the first base station  12  transmits first local data and the second base station  16  transmits second local data using the modulation layer with lesser reliability. In an additional embodiment of the present invention, the base stations  12 ,  16  both transmit nominal resolution broadcast data using the modulation layer with greater reliability, and transmit enhanced resolution broadcast data using the modulation layer with lesser reliability. In an alternate embodiment of the present invention, the base stations  12 ,  16  both transmit basic programming data using the modulation layer with greater reliability, and transmit supplemental programming data using the modulation layer with lesser reliability. In yet another embodiment of the present invention, the base stations  12 ,  16  both may transmit broadcast video data. In an alternate embodiment of the present invention, the base stations  12 ,  16  may both transmit broadcast audio data. 
     In one embodiment of the present invention, the higher modulation layer data may include RF communications system control channel data. The base stations  12 ,  16  may both transmit broadcast data using lower modulation symbols  48 , and the first base station  12  may transmit unicast data directed to the first mobile terminal  20  using higher modulation symbols  50 . In an alternate embodiment of the present invention, the second base station  16  may transmit unicast data directed to the second mobile terminal  28  using one of the modulation symbols  48 ,  50 , and transmit unicast data directed to the third mobile terminal  32  using the other of the modulation symbols  48 ,  50 . The modulation layer with greater reliability is used with the data link with the lower signal margin, and the modulation layer with lower reliability is used with the data link with the greater signal margin. 
     The present invention includes transmitting different information using different modulation layers. Different embodiments will allocate the different information to the different modulation layers in different ways. Those skilled in the art will understand the concepts of the invention and will recognize applications of these concepts beyond the specific examples given. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims. Specifically, the different information may be associated with any of the different modulation layers in any order. 
       FIG. 7A  shows the alignment of lower modulation layer data  102  with higher modulation layer data  104  in one embodiment of the present invention. The lower modulation layer data  102  includes a first lower layer sample  106 , a second lower layer sample  108 , a third lower layer sample  110 , and a fourth lower layer sample  112 . The higher modulation layer data  104  includes a first higher layer sample  114 , a second higher layer sample  116 , a third higher layer sample  118 , and a fourth higher layer sample  120 . The lower layer samples  106 ,  108 ,  110 ,  112  are time aligned with the higher layer samples  114 ,  116 ,  118 ,  120 . In mixing a system with phase and amplitude modulation, such as QAM, with a system having only phase modulation, such as QPSK, the constellation points of the QAM system may not directly align with the constellation points of the QPSK system; therefore, time-shifting the lower modulation layer data  102  from the higher modulation layer data  104  may improve signal margins. In an alternate embodiment of the present invention, the lower modulation layer data  102  is time-shifted from the higher modulation layer data  104  as illustrated in  FIG. 7B . The higher layer samples  114 ,  116 ,  118  are time-shifted from the lower layer samples  106 ,  108 ,  110 ,  112 , which may help average the higher layer samples  114 ,  116 ,  118  to make the lower layer samples  106 ,  108 ,  110 ,  112  line up closer to nominal constellation points of the QPSK system. A lower modulation rate for the lower modulation layer data  102  may further improve the impact of averaging. Even though the lower modulation layer data  102  is time-shifted from the higher modulation layer data  104 , which means the lower modulation symbol  48  is time-shifted from the higher modulation symbol  50 , both modulation symbols  48 ,  50  fall within one modulation symbol period and are effectively transmitted simultaneously. 
       FIG. 8A  shows time multiplexed or TDM data included in the higher modulation layer data  104 . The higher modulation layer data  104  includes a first sample of first time multiplexed data  122 , a first sample of second time multiplexed data  124 , a second sample of first time multiplexed data  126 , and a second sample of second time multiplexed data  128 . The samples  122 ,  126  of the first time multiplexed data are interspersed with the samples  124 ,  128  of the second time multiplexed data. Different channels, sub-channels, or unrelated data streams may be included in the higher modulation layer data  104 . Other embodiments of the present invention may include TDM data in the higher modulation layer data  104 , the lower modulation layer data  102 , or both. 
       FIG. 8B  shows two single-carrier orthogonal frequency division multiplexing (OFDM) sub-carriers included in the higher modulation layer data  104 . The higher modulation layer data  104  includes a first sample of a first OFDM sub-carrier  130 , a first sample of a second OFDM sub-carrier  132 , a second sample of the first OFDM sub-carrier  134 , and a second sample of the second OFDM sub-carrier  136 . The samples  130 ,  134  of the first OFDM sub-carrier are interspersed with the samples  132 ,  136  of the second OFDM sub-carrier. Other embodiments of the present invention may include OFDM data in the higher modulation layer data  104 , the lower modulation layer data  102 , or both. 
       FIG. 9  adds MIMO antennas to the base stations and some of the terminals illustrated in  FIG. 1 . The first base station  12  includes a second antenna port ANT 2  coupled to a first MIMO base station antenna  138 . The second base station  16  includes a second antenna port ANT 2  coupled to a second MIMO base station antenna  140 . The first mobile terminal  20  includes a second antenna port ANT 2  coupled to a first MIMO mobile terminal antenna  142 . The fixed terminal  24  includes a second antenna port ANT 2  coupled to a fixed MIMO antenna  144 . The third mobile terminal  32  includes a second antenna port ANT 2  coupled to a second MIMO mobile terminal antenna  146 . The second mobile terminal  28  does not have a MIMO antenna. The RF communications system  10  illustrated in  FIG. 9  may represent a communications system that has been upgraded to include MIMO capability. The second mobile terminal  28  does not have MIMO capability and may represent a previous generation UE, or may be a low cost, reduced functionality UE sold for use in the MIMO RF communications system  10 . By using the present invention, the second mobile terminal  28  may be able to transmit and receive lower modulation layer data  102  to and from the base stations  12 ,  16 , and the other terminals  20 ,  24 ,  32  may be able to transmit and receive both modulation layer data  102 ,  104  to and from the base stations  12 ,  16 . 
     The present invention includes processing different information streams using different modulation layers, such as MIMO. MIMO systems use multiple antennas for each base station or terminal. The multiple antennas may provide spatial diversity, which allows spatial multiplexing. Spatial multiplexing may allow different information to be transmitted and received from each of the multiple antennas. Other systems may use multiple antennas for diversity. Data from single antenna systems, such as the RF communications system  10  illustrated in  FIG. 1  is known as single input single output (SISO) data. Data from multiple antenna systems that has different information associated with each antenna, such as the RF communications system  10  illustrated in  FIG. 9  is known as MIMO data. By using SISO data with the lower modulation layer data  102  and MIMO data with the higher modulation layer data  104 , the RF communications system  10  may be backward compatible by supporting previous generation communications protocols and present communications protocols. 
       FIG. 10  shows SISO data included in the lower modulation layer data  102 , and two MIMO sub-channels included in the higher modulation layer data  104 . The lower modulation layer data  102  includes a first SISO data sample  148 , a second SISO data sample  150 , a third SISO data sample  152 , and a fourth SISO data sample  154 . The higher modulation layer data  104  includes a first sample of a first MIMO sub-channel  156 , a first sample of a second MIMO sub-channel  158 , a second sample of the first MIMO sub-channel  160 , and a second sample of the second MIMO sub-channel  162 . The samples  156 ,  160  of the first MIMO sub-channel are interspersed with the samples  158 ,  162  of the second MIMO sub-channel. Other embodiments of the present invention may include MIMO data in the higher modulation layer data  104 , the lower modulation layer data  102 , or both. 
       FIG. 11  shows one embodiment of the present invention used with MIMO transmitter circuitry  164 . First transmit circuitry  166  receives both lower modulation layer data LML and first higher modulation layer data HML 1 . The first transmit circuitry  166  provides a first modulated RF signal to a first power amplifier  168 , which provides an amplified first modulated RF signal to the first antenna port ANT 1 . The first modulated RF signal is based on both the lower modulation layer data LML and the first higher modulation layer data HML 1 . Second transmit circuitry  170  receives both the lower modulation layer data LML and second higher modulation layer data HML 2 . The second transmit circuitry  170  provides a second modulated RF signal to a second power amplifier  172 , which provides an amplified second modulated RF signal to the second antenna port ANT 2 . The second modulated RF signal is based on both the lower modulation layer data LML and the second higher modulation layer data HML 2 . The lower modulation layer data LML is sent to both antenna ports ANT 1 , ANT 2 . The first higher modulation layer data HML 1  is sent to only the first antenna port ANT 1 . The second higher modulation layer data HML 2  is sent to only the second antenna port ANT 2 . In one embodiment of the present invention, the lower modulation layer data LML includes basic broadcast data, the first higher modulation layer data HML 1  includes first supplemental data, and the second higher modulation layer data HML 2  includes second supplemental data. The second mobile terminal  28  may receive the basic broadcast data, and the other terminals  20 ,  24 ,  32  may receive the basic broadcast data, the first supplemental data, and the second supplemental data. All of the modulation layer data LML, HML 1 , HML 2  is transmitted simultaneously. Each of the first and second higher modulation layer data HML 1 , HML 2  is a MIMO sub-channel. The RF communications system  10  may have multiple base stations such that each base station has multiple antennas providing MIMO capability. All of the base stations and antennas may be used to form an SFN using the same lower modulation layer data LML. The first and second higher modulation layer data HML 1 , HML 2  may be transmitted from different base stations, or an antenna on one base station may transmit the first higher modulation layer data HML 1  and an antenna on a different base station may transmit the second higher modulation layer data HML 2 . 
       FIG. 12  shows details of the first base station  12  illustrated in  FIG. 1 . The basic architecture of the first base station  12  may include a receiver front end  174 , a radio frequency transmitter section  176 , an antenna  178 , a duplexer or switch  180 , a baseband processor  182 , a control system  184 , and a frequency synthesizer  186 . The receiver front end  174  receives information bearing radio frequency signals from one or more remote transmitters provided by other base stations, terminals, or other user equipment. A low noise amplifier (LNA)  188  amplifies the signal. A filter circuit  190  minimizes broadband interference in the received signal, while down conversion and digitization circuitry  192  down converts the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. The receiver front end  174  typically uses one or more mixing frequencies generated by the frequency synthesizer  186 . The baseband processor  182  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor  182  is generally implemented in one or more digital signal processors (DSPs). 
     On the transmit side, the baseband processor  182  receives digitized data, which may represent voice, data, or control information, from the control system  184 , which it encodes for transmission. The encoded data is output to the transmitter  176 , where it is used by a modulator  194  to modulate a carrier signal that is at a desired transmit frequency. Power amplifier circuitry  196  amplifies the modulated carrier signal to a level appropriate for transmission, and delivers the amplified and modulated carrier signal to the antenna  178  through the duplexer or switch  180 . 
     The following description provides an overview of a wireless communication environment and the architecture of a base station, or like access point, and a mobile terminal, which may be used in an OFDM and MIMO environment. 
     With reference to  FIG. 13 , a base station controller (BSC)  198  controls wireless communications within multiple cells  200 , which are served by corresponding base stations (BS)  202 . In general, each base station  202  facilitates communications using OFDM with mobile terminals  204 , which are within the cell  200  associated with the corresponding base station  202 . The movement of the mobile terminals  204  in relation to the base stations  202  results in significant fluctuation in channel conditions. As illustrated, the base stations  202  and mobile terminals  204  may include multiple antennas to provide spatial diversity for communications. 
     A high level overview of the mobile terminals  204  and base stations  202  of the present invention is provided prior to delving into structural and functional details. With reference to  FIG. 14 , a base station  202  configured according to one embodiment of the present invention is illustrated. The base station  202  generally includes a control system  206 , a baseband processor  208 , transmit circuitry  210 , receive circuitry  212 , multiple antennas  214 , and a network interface  216 . The receive circuitry  212  receives radio frequency signals bearing information from one or more remote transmitters provided by mobile terminals  204  (illustrated in  FIG. 15 ). Preferably, a low noise amplifier and a filter (not shown) cooperate to amplify and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
     The baseband processor  208  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations. As such, the baseband processor  208  is generally implemented in one or more digital signal processors (DSPs) or application-specific integrated circuits (ASICs). The received information is then sent across a wireless network via the network interface  216  or transmitted to another mobile terminal  204  serviced by the base station  202 . 
     On the transmit side, the baseband processor  208  receives digitized data, which may represent voice, data, or control information, from the network interface  216  under the control of the control system  206 , and encodes the data for transmission. The encoded data is output to the transmit circuitry  210 , where it is modulated by a carrier signal having a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas  214  through a matching network (not shown). Modulation and processing details are described in greater detail below. 
     With reference to  FIG. 15 , a mobile terminal  204  configured according to one embodiment of the present invention is illustrated. Similarly to the base station  202 , the mobile terminal  204  will include a control system  218 , a baseband processor  220 , transmit circuitry  222 , receive circuitry  224 , multiple antennas  226 , and user interface circuitry  228 . The receive circuitry  224  receives radio frequency signals bearing information from one or more base stations  202 . Preferably, a low noise amplifier and a filter (not shown) cooperate to amplify and remove broadband interference from the signal for processing. Downconversion and digitization circuitry (not shown) will then downconvert the filtered, received signal to an intermediate or baseband frequency signal, which is then digitized into one or more digital streams. 
     The baseband processor  220  processes the digitized received signal to extract the information or data bits conveyed in the received signal. This processing typically comprises demodulation, decoding, and error correction operations, as will be discussed on greater detail below. The baseband processor  220  is generally implemented in one or more digital signal processors (DSPs) and application specific integrated circuits (ASICs). 
     For transmission, the baseband processor  220  receives digitized data, which may represent voice, data, or control information, from the control system  218 , which it encodes for transmission. The encoded data is output to the transmit circuitry  222 , where it is used by a modulator to modulate a carrier signal that is at a desired transmit frequency or frequencies. A power amplifier (not shown) will amplify the modulated carrier signal to a level appropriate for transmission, and deliver the modulated carrier signal to the antennas  226  through a matching network (not shown). Various modulation and processing techniques available to those skilled in the art are applicable to the present invention. 
     In OFDM modulation, the transmission band is divided into multiple, orthogonal carrier waves. Each carrier wave is modulated according to the digital data to be transmitted. Because OFDM divides the transmission band into multiple carriers, the bandwidth per carrier decreases and the modulation time per carrier increases. Since the multiple carriers are transmitted in parallel, the transmission rate for the digital data, or symbols, on any given carrier is lower than when a single carrier is used. 
     OFDM modulation may require the performance of an Inverse Fast Fourier Transform (IFFT) on the information to be transmitted. For demodulation, the performance of a Fast Fourier Transform (FFT) on the received signal is required to recover the transmitted information. In practice, the IFFT and FFT are provided by digital signal processing carrying out an Inverse Discrete Fourier Transform (IDFT) and Discrete Fourier Transform (DFT), respectively. Accordingly, the characterizing feature of OFDM modulation is that orthogonal carrier waves are generated for multiple bands within a transmission channel. The modulated signals are digital signals having a relatively low transmission rate and capable of staying within their respective bands. The individual carrier waves are not modulated directly by the digital signals. Instead, all carrier waves are modulated at once by IFFT processing. 
     In one embodiment, OFDM is used for at least the downlink transmission from the base stations  202  to the mobile terminals  204 . Each base station  202  is equipped with n transmit antennas  214 , and each mobile terminal  204  is equipped with m receive antennas  226 . Notably, the respective antennas can be used for reception and transmission using appropriate duplexers or switches and are so labeled only for clarity. 
     With reference to  FIG. 16 , a logical OFDM transmission architecture is provided according to one embodiment. Initially, the base station controller  198  may send channel quality indicator (CQI) information based on carrier-to-interference ratios (CIR) to the base station  202 . Additionally, the base station controller  198  will send data to be transmitted to various mobile terminals  204  to the base station  202 . The base station  202  may use the CQIs associated with the mobile terminals to schedule the data for transmission as well as select appropriate coding and modulation for transmitting the scheduled data. The CQIs may be directly from the mobile terminals  204  or determined at, the base station  202  based on information provided by the mobile terminals  204 . In either case, the CQI for each mobile terminal  204  is a function of the degree to which the channel amplitude (or response) varies across the OFDM frequency band. 
     Scheduled data  230 , which is a stream of bits, is scrambled in a manner reducing the peak-to-average power ratio associated with the data using data scrambling logic  232 . A cyclic redundancy check (CRC) for the scrambled data is determined and appended to the scrambled data using CRC adding logic  234 . Next, channel coding is performed using channel encoder logic  236  to effectively add redundancy to the data to facilitate recovery and error correction at the mobile terminal  204 . Again, the channel coding for a particular mobile terminal  204  is based on the CQI. The channel encoder logic  236  uses known Turbo encoding techniques in one embodiment. The encoded data is then processed by rate matching logic  238  to compensate for the data expansion associated with encoding. 
     Bit interleaver logic  240  systematically reorders the bits in the encoded data to minimize the loss of consecutive data bits. The resultant data bits are systematically mapped into corresponding symbols depending on the chosen baseband modulation by mapping logic  242 . Preferably, Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Key (QPSK) modulation is used. The degree of modulation is preferably chosen based on the CQI for the particular mobile terminal. The symbols may be systematically reordered to further bolster the immunity of the transmitted signal to periodic data loss caused by frequency selective fading using symbol interleaver logic  244 . 
     At this point, groups of bits have been mapped into symbols representing locations in an amplitude and phase constellation. When spatial diversity is desired, blocks of symbols are then processed by space-time block code (STC) encoder logic  246 , which modifies the symbols in a fashion making the transmitted signals more resistant to interference and more readily decoded at a mobile terminal  204 . The STC encoder logic  246  will process the incoming symbols and provide n outputs corresponding to the number of transmit antennas  214  for the base station  202 . The control system  206  and/or baseband processor  208  will provide a mapping control signal to control STC encoding. At this point, assume the symbols for the n outputs are representative of the data to be transmitted and capable of being recovered by the mobile terminal  204 . See A. F. Naguib, N. Seshadri, and A. R. Calderbank, “Applications of space-time codes and interference suppression for high capacity and high data rate wireless systems,” Thirty-Second Asilomar Conference on Signals, Systems &amp; Computers, Volume 2, pp. 1803-1810, 1998, which is incorporated herein by reference in its entirety. 
     For the present example, assume the base station  202  has two antennas  214  (n=2) and the STC encoder logic  246  provides two output streams of symbols. Accordingly, each of the symbol streams output by the STC encoder logic  246  is sent to a corresponding IFFT processor  248 , illustrated separately for ease of understanding. Those skilled in the art will recognize that one or more processors may be used to provide such digital signal processing, alone or in combination with other processing described herein. The IFFT processors  248  will preferably operate on the respective symbols to provide an inverse Fourier Transform. The output of the IFFT processors  248  provides symbols in the time domain. The time domain symbols are grouped into frames, which are associated with a prefix by like insertion logic  250 . Each of the resultant signals is up-converted in the digital domain to an intermediate frequency and converted to an analog signal via the corresponding digital up-conversion (DUC) and digital-to-analog (D/A) conversion circuitry  252 . The resultant (analog) signals are then simultaneously modulated at the desired RF frequency, amplified, and transmitted via the RF circuitry  254  and antennas  214 . Notably, pilot signals known by the intended mobile terminal  204  are scattered among the sub-carriers. The mobile terminal  204 , which is discussed in detail below, will use the pilot signals for channel estimation. 
     Reference is now made to  FIG. 17  to illustrate reception of the transmitted signals by a mobile terminal  204 . Upon arrival of the transmitted signals at each of the antennas  226  of the mobile terminal  204 , the respective signals are demodulated and amplified by corresponding RF circuitry  256 . For the sake of conciseness and clarity, only one of the two receive paths is described and illustrated in detail. Analog-to-digital (A/D) converter and down-conversion circuitry  258  digitizes and downconverts the analog signal for digital processing. The resultant digitized signal may be used by automatic gain control circuitry (AGC)  260  to control the gain of the amplifiers in the RF circuitry  256  based on the received signal level. 
     Initially, the digitized signal is provided to synchronization logic  262 , which includes coarse synchronization logic  264 , fine synchronization logic  266 , and frequency offset and clock estimation logic  268 : The coarse synchronization logic  264  buffers several OFDM symbols and calculates an auto-correlation between the two successive OFDM symbols. A resultant time index corresponding to the maximum of the correlation result determines a fine synchronization search window, which is used by fine synchronization logic  266  to determine a precise framing starting position based on the headers. The output of the fine synchronization logic  266  facilitates frame acquisition by frame alignment logic  270 . Proper framing alignment is important so that subsequent FFT processing provides an accurate conversion from the time to the frequency domain. The fine synchronization algorithm is based on the correlation between the received pilot signals carried by the headers and a local copy of the known pilot data. Once frame alignment acquisition occurs, the prefix of the OFDM symbol is removed with prefix removal logic  272  and resultant samples are sent to frequency offset correction logic  274 , which compensates for the system frequency offset caused by the unmatched local oscillators in the transmitter and the receiver. The synchronization logic  262  may include the frequency offset and dock estimation logic  268 , which is based on the headers to help estimate such effects on the transmitted signal and provide those estimations, to the correction logic  274  to properly process OFDM symbols. 
     At this point, the OFDM symbols in the time domain are ready for conversion to the frequency domain using FFT processing logic  276 . The results are frequency domain symbols, which are sent to processing logic  278 . The processing logic  278  extracts the scattered pilot signal using scattered pilot extraction logic  280 , determines a channel estimate based on the extracted pilot signal using channel estimation logic  282 , and provides channel responses for all sub-carriers using channel reconstruction logic  284 . In order to determine a channel response for each of the sub-carriers; the pilot signal is essentially multiple pilot symbols that are scattered among the data symbols throughout the OFDM sub-carriers in a known pattern in both time and frequency.  FIG. 18  illustrates an exemplary scattering of pilot symbols among available sub-carriers over a given time and frequency plot in an OFDM environment. Continuing with  FIG. 17 , the processing logic compares the received pilot symbols with the pilot symbols that are expected in certain sub-carriers at certain times to determine a channel response for the sub-carriers in which pilot symbols were transmitted. The results are interpolated to estimate a channel response for most, if not all, of the remaining sub-carriers for which pilot symbols were not provided. The actual and interpolated channel responses are used to estimate an overall channel response, which includes the channel responses for most, if not all, of the sub-carriers in the OFDM channel. 
     The frequency domain symbols and channel reconstruction information, which are derived from the channel responses for each receive path are provided to an STC decoder  286 , which provides STC decoding on both received paths to recover the transmitted symbols. The channel reconstruction information provides equalization information to the STC decoder  286  sufficient to remove the effects of the transmission channel when processing the respective frequency domain symbols 
     The recovered symbols are placed back in order using symbol de-interleaver logic  288 , which corresponds to the symbol interleaver logic  244  of the transmitter. The de-interleaved symbols are then demodulated or de-mapped to a corresponding bitstream using de-mapping logic  290 . The bits are then de-interleaved using bit de-interleaver logic  292 , which corresponds to the bit interleaver logic  240  of the transmitter architecture. The de-interleaved bits are then processed by rate de-matching logic  294  and presented to channel decoder logic  296  to recover the initially scrambled data and the CRC checksum. Accordingly, CRC logic  298  removes the CRC checksum, checks the scrambled data in traditional fashion, and provides it to the de-scrambling logic  300  for de-scrambling using the known base station de-scrambling code to recover the originally transmitted data  302 . 
     In parallel to recovering the data  302 , a CQI, or at least information sufficient to create a CQI at the base station  202 , is determined and transmitted to the base station  14 . As noted above, the CQI in a preferred embodiment is a function of the carrier-to-interference ratio (CIR), as well as the degree to which the channel response varies across the various sub-carriers in the OFDM frequency band. For this embodiment, the channel gain for each sub-carrier in the OFDM frequency band being used to transmit information are compared relative to one another to determine the degree to which the channel gain varies across the OFDM frequency band. Although numerous techniques are available to measure the degree of variation, one technique is to calculate the standard deviation of the channel gain for each sub-carrier throughout the OFDM frequency band being used to transmit data. 
     Continuing with  FIG. 17 , a relative variation measure may be determined by providing the channel response information from the channel estimation function  282  to a channel variation analysis function  304 , which will determine the variation and channel response for each of the sub-carriers in the OFDM frequency band, and if standard deviation is used, calculate the standard deviation associated with the frequency response. As noted, channel gain is a preferred measure of the channel response for calculating a CQI  306 . The channel gain may be quantified based on a relative amplitude of the channel frequency response in decibels (dB), and as such, the amplitude of the channel frequency response may be represented by H dB (k), which is a function of a sub-carrier index k, where k=1 . . . k MIN , . . . k MAX , . . . k FFT . Notably, k FFT  is the number of sub-carriers in the entire OFDM frequency band, and the sub-carriers k MIN  through k MAX  represent the sub-carriers within the OFDM frequency band that are actually used to transmit data. Typically, a range of sub-carriers at either end of the range of sub-carriers are not used, in order to minimize interference with other transmissions. As such, the degree of variation of the amplitude of the channel response may be determined only for the range of sub-carriers being used to transmit data (k MIN  through k MAX ). The standard deviation of the channel response across the usable range of sub-carriers is calculated as follows: 
                     std   =         1       N   u     -   1       ⁢       ∑     k   MIN       k   MAX       ⁢       (         H   dB     ⁡     (   k   )       -       H   _     dB       )     2             ,           Eq   .           ⁢   1               
where N u  is the number of usable sub-carriers, H db (k) is the log amplitude of the channel frequency response, and  H   db , is the mean of the log amplitude of the channel response across the usable range of sub-carriers or a subset thereof.
 
     In a multiple-input multiple-output (MIMO) system where there are multiple transmit and multiple receive antennas  214 ,  226  each link corresponding to transmit/receive antenna pairs will have a unique CQI. An aggregate CQI, or set of aggregate CQIs, may be required for the overall MIMO set of links. To determine the aggregate CQIs, the channel frequency response and CIR for each transmit and receive antenna pair is determined. 
     For multiple receive antennas  226 , the multiple channel frequency responses are combined, to provide for the diversity achieved from the multiple receive antennas  226 . This combining is an averaging of the power of the respective channel frequency responses across the OFDM frequency band. The channel variation measure is then determined across the combined channel frequency response. The CIR values for the respective multiple receive antennas  226  are combined by summing. 
     For multiple transmit antennas  214 , the modification to the CQI will depend on the particular space time coding technique employed to reflect the method by which the transmit diversity is being achieved by the code and used by the system. Some schemes, such as transmit diversity, will require that the respective channel frequency responses from the multiple transmit antennas  214  be combined as described for the multiple receive antennas  226  by averaging the power of the channel frequency responses across the OFDM frequency band. The channel variation measure is made across the combined frequency response. Further, the CIR values for the multiple transmit antennas  214  are also combined. For other schemes, a separate CQI may be determined for each transmit antenna  214  and relayed back to the base station  202 . The base station  202  may use the CQI per transmit antenna  214  to separately adapt the modulation and coding on the data transmitted on the respective transmit antennas  214 . 
     Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present invention. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

Metadata:
Filing Date: 20110714
Publication Date: 20120821
Grant Date: 20120821
Priority Date: 20061230
Inventors: STEER DAVID G.
Assignee: APPLE INC
CPC Classifications: [{"code": "H04L27/2604", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0224", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0202", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/3488", "inventive": true, "first": true, "tree": "[]"}, {"code": "H04L27/183", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0202", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L25/0224", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/183", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/2604", "inventive": true, "first": false, "tree": "[]"}, {"code": "H04L27/3488", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 39583828