Patent Publication Number: US-2015085801-A1

Title: Wireless local area network using tv white space spectrum and long term evolution system architecture

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/597,607, filed Aug. 29, 2012, titled “Wireless Local Area Network Using TV White Space Spectrum and Long Term Evolution System Architecture”, which is a continuation of U.S. patent application Ser. No. 12/363,319, filed Jan. 30, 2009, titled “Wireless Local Area Network Using TV White Space Spectrum and Long Term Evolution System Architecture”, now U.S. Pat. No. 8,335,204, which are hereby incorporated by reference as if fully set forth herein. 
    
    
     BACKGROUND 
     This invention relates in general to data communications within a wireless local area network (WLAN) and, in particular, to a WLAN using available TV white space spectrum and Long Term Evolution (LTE) system architecture for data communications. 
     Data communication within WLANs is now generally accomplished using WiFi implemented using one of the IEEE 802.11 standards. The 802.11b and 802.11g standards are designed to operate in the 2.4 GHz band using Direct Sequence Spread Spectrum (DSSS) technology. The 802.11 n standard is designed to operate in the 2.4 GHz or the 5 GHz bands. 
     While WiFi works well, the high frequency signals do not readily penetrate obstructions, so a high transmit power must be used. This has raised health concerns that remain unaddressed. Furthermore, the wireless distribution of new data-intensive services such as High Definition Television (HDTV) and multimedia communications signals can undesirably degrade WLAN performance; and, the quality of service (QoS) of the HDTV or multimedia signals can be adversely affected if the WLAN is simultaneously used for the delivery of other data intensive services, such as internet access. 
     A radio standard called Long Term Evolution (LTE) has been developed by the 3rd Generation Partnership Project (3GPP). The goals of LTE are the provision of an all Internet Protocol (IP) packet network with faster download and upload speeds and reduced latency. 
       FIG. 1  is a schematic diagram of an LTE generic downlink radio frame structure  100 . Each downlink radio frame  100  includes twenty time slots  102  numbered from 0 to 19 having a duration of 0.5 ms each. Two adjacent time slots make up a subframe  104  having a duration of 1 ms. Each downlink frame  100  has a duration of 10 ms. 
       FIG. 2  is a schematic diagram of the structure of each LTE downlink time slot  102 . The smallest time-frequency unit for downlink transmission is called a resource element  106 , which constitutes one symbol on one sub-carrier. A group of 12 sub-carriers that are contiguous in frequency within the time slot  102  form a resource block  108 . When the downlink frame structure  100  uses a normal cyclic prefix, the 12 contiguous sub-carriers in the resource block  108  have a sub-carrier spacing of 15 kHz with 7 consecutive symbols in each downlink time slot 102. The cyclic prefix is appended to each symbol as a guard interval. The symbol plus the cyclic prefix form the resource element  106 . Consequently, the resource block  108  has 84 resource elements (12 sub-carriers×7 symbols) corresponding to one time slot  102  in the time domain and 180 kHz (12 sub-carriers×15 kHz spacing) in the frequency domain. The size of a resource block  108  is the same for all bandwidths. In the frequency domain, the number of available sub-carriers can range from 76 sub-carriers when the transmission bandwidth is 1.25 MHz, to 1201 sub-carriers when the transmission bandwidth is 20 MHz. 
     LTE has been designed to be very robust and supports data rates of up to 100+ Mbps on the downlink and 50+ Mbps on the uplink. Although it is optimized for user equipment travel speeds of 0-15 km/h, travel speeds of 15-120 km/h are supported with high efficiency. To accomplish this level of performance, “reference” or “pilot” symbols are inserted in predetermined resource element positions within each transmitted resource block  108 . The pilot symbols are used by receiver channel estimation algorithms to correct for received signal distortions. 
       FIG. 3  is a schematic diagram of some of the pilot symbols  120  transmitted in the LTE downlink frame  100 , for a single antenna case. The pilot symbols  120  are transmitted at OFDM symbol positions 0 and 4 of each time slot  102 . 
     In May of 2004, the Federal Communications Commission (FCC) approved a Notice of Proposed Rulemaking to allow a new generation of wireless devices to use vacant television frequencies (TV white spaces) on an unlicensed basis. These TV white spaces are frequency channels allocated for television broadcasting that will not be used in given geographic areas after Feb. 17, 2009. Specifically, the FCC will allow unlicensed operation in the spectrum used by TV channels 5 and 6 (76-88 MHz); 7 through 13 (174-213 MHz); 14 through 36 (470-608 MHz); and, 38 through 51 (614-698 MHz). 
     Many proposals exist for using the unlicensed TV white space spectrum. For example, it has been suggested that Wireless Regional Area Networks (WRANs) could be established to provide high-speed internet access to single family dwellings, multiple dwelling units and small businesses. The WRANs would operate using the IEEE 802.22 architecture over the TV white space spectrum with a fixed deployment and a larger coverage (25˜30 km range). 
     While these proposals have merit, they do not provide an efficient solution to the developing congestion in WLANs due to the emerging requirement to distribute HDTV signals wirelessly in a home environment. Furthermore, they do not provide interoperability with other systems or devices that use the LTE system architecture. 
     Therefore there exists a need for a local area network that uses the TV white space spectrum and the LTE system architecture. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a wireless local area network a method of data communications within the wireless local area network using the TV white space spectrum and the LTE system architecture. 
     The invention therefore provides a wireless local area network, comprising: a local area network gateway that transmits modified Long Term Evolution (LTE) downlink frames in which at least a predetermined subset of pilot symbol positions used in the LTE downlink frames to transmit pilot symbols for channel estimation are filled with control data symbols; and a data sink that receives the modified LTE frames and extracts the control data symbols from the predetermined subset of pilot symbol positions. 
     The invention further provides a local area network gateway comprising a transceiver that transmits modified Long Term Evolution (LTE) downlink frames in which a predetermined subset of the pilot symbols used for channel estimation in the modified LTE downlink frames are replaced with control data symbols. 
     The invention yet further provides a data sink in a local area network, comprising a Long Term Evolution (LTE) frame processor that processes modified LTE downlink frames transmitted by a local area network gateway and extracts control data from a subset of pilot symbol positions used to carry the control data in the modified LTE downlink frame. 
     The invention still further provides a method of data communications in a wireless local area network, comprising: transmitting within the wireless local area network modified Long Term Evolution (LTE) downlink frames in which at least a predetermined subset of the pilot symbol positions used in the LTE downlink frames to transmit pilot symbols for channel estimation are filled with control data symbols; and on receipt at a data sink in the wireless local area network of a one of the modified LTE downlink frames, demodulating the modified LTE downlink frame and extracting the control data symbols from the predetermined subset of the pilot symbol positions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, in which: 
         FIG. 1  is a schematic diagram of a prior art LTE downlink frame structure of type-1; 
         FIG. 2  is a schematic diagram of a prior art downlink slot structure for the downlink frame shown in  FIG. 1 ; 
         FIG. 3  is a schematic diagram of some of the pilot (reference) symbols transmitted in two of the prior art downlink slots shown in  FIG. 2 ; 
         FIG. 4  is a schematic diagram of one embodiment of a WLAN in accordance with the invention; 
         FIG. 5  is a flow diagram illustrating a high-level overview of some of the actions performed during startup and downlink frame processing by a WLAN gateway shown in  FIG. 4 ; 
         FIG. 6  is a flow diagram illustrating a high-level overview of some of the actions performed during startup and downlink frame processing by a WLAN receiver shown in  FIG. 4 ; 
         FIG. 7  is a schematic diagram of a proportion of the pilot symbols transmitted in a LTE downlink frame structure in accordance with the invention showing released pilot symbol positions used for control data transmission in the WLAN in accordance with the invention; 
         FIG. 8  is a schematic diagram illustrating a first step in one method of interpolating channel estimates using the LTE downlink frame structure in accordance with the invention; 
         FIG. 9  is a schematic diagram illustrating the results of a second step in the method of interpolating channel estimates shown in  FIG. 8 ; 
         FIG. 10  is a schematic diagram illustrating a third step of the method of interpolating channel estimates shown in  FIG. 8 ; 
         FIG. 11  is a schematic diagram illustrating the results of the second step of the method of interpolating channel estimates shown in  FIG. 10 ; 
         FIG. 12  is a schematic diagram illustrating a method of interpolating channel estimates in the time domain using linear interpolation between computed channel estimates; 
         FIG. 13  is a schematic diagram illustrating a method of interpolating channel estimates in the time domain using cubic spline interpolation between computed channel estimates; 
         FIG. 14  is a schematic diagram illustrating a first step in another method of interpolating channel estimates using the LTE downlink frame structure in accordance with the invention, and the results of the first step; and 
         FIG. 15  is a schematic diagram illustrating the results of the first step of the method of interpolating channel estimates shown in  FIG. 14 , and a second step in that method of interpolating the channel estimates in the time domain. 
     
    
    
     DETAILED DESCRIPTION 
     The invention provides a wireless local area network (WLAN) in which a modified LTE downlink frame and the TV white space spectrum are used for data communications. A WLAN gateway is connected to at least one data source. The WLAN gateway wirelessly distributes source data and/or control data to a LTE transceiver or receiver associated with each data sink in the WLAN. In the modified LTE downlink frame a predefined subset of the pilot (reference) symbol positions are used to carry the control data to the data sinks. The source data (payload) capacity of each modified LTE radio frame is unaffected by the transmission of the control data, so control data may be distributed without affecting network throughput. The data capacity and the efficiency of the WLAN are thereby improved. The WLAN gateway has an effective transmit range of up to 30 meters at a fraction of the transmit power of most 802.11 access points (AP) currently in use. The WLAN gateway can also operate in the same environment as an 802.11 AP without interference because of the significant difference in operating frequencies. The WLAN has many benefits and uses, including in-home wireless distribution of high definition television (HDTV) signals, and compatibility with other LTE systems and devices. 
       FIG. 4  is a schematic diagram of a WLAN  400 , in accordance with one embodiment of the invention. A WLAN gateway  402  has input ports  403  that are connected to at least one data source  404 . The data source(s)  404  delivers “source data” to the WLAN  400 . 
     The term “source data” means any information in any format derived from any data source  404 , including but not limited to: customer premises equipment that receives any one or more of telephone, radio, television, multimedia, data or internet content in any protocol delivered via a telephone line, coaxial cable, optical fiber, microwaves, radio waves, television signals or satellite signals. 
     The WLAN gateway  402  includes a spectrum sensing unit  406  equipped with a spectrum sensing antenna  408 . The spectrum sensing antenna  408  is used by the spectrum sensing unit  406  to detect over-the-air TV band signals in the TV white space spectrum. Information about the detected over-the-air TV band signals is passed by the spectrum sensing unit  406  to a spectrum manager  410 . The spectrum manager  410  uses the detected signal information to select available TV white space spectrum for unlicensed use by the WLAN  400 , as will be explained in more detail below with reference to  FIG. 5 . 
     The TV white space spectrum selected by the spectrum manager  410  is passed to a white space LTE transceiver  412 , which receives, via a white space LTE Tx/Rx Antenna  414 , source data requests sent from data sinks  416 ,  418  in LTE uplink frames (not shown). The LTE transceiver  412  distributes the source data in LTE downlink frames prepared by a frame processor  413 . The LTE downlink frames are transmitted to the data sinks  416 ,  418  using the TV white space LTE Tx/Rx antenna  414 . 
     The term “data sink” means any piece of user equipment in the WLAN  400  equipped with a TV white space LTE transceiver/receiver. A data sink may include, but is not limited to: any computer; any entertainment or home theatre component or device, including a HDTV; any commercial or household appliance; any environmental control system, device or sensor; any security control system, device or sensor; any entrance control system, device or sensor; or, any access control system, device or sensor. 
     The WLAN gateway  402  also distributes control data to the data sinks  416 ,  418 , as required, using the white space LTE Tx/Rx antenna  414 . 
     The term “control data” means any information in any format transmitted in a predetermined subset of pilot positions in the modified LTE downlink frames. The control data may communicate information of any kind to the data sink, and/or control the configuration, operation or behavior of the data sink. For example, the control data may be used to enable: an identification signal for co-existence of two or more WLANs  400  that operate in close proximity; provide a Consumer Electronic Control (CEC) compliant interaction channel with a home entertainment network; provide a High-bandwidth Digital Content Protection (HDCP) or Digital Transmission Content Protection (DTCP) type content protection scheme with Copy Protection for Recordable Media (CPRM) support; provide remote appliance or system control; or, permit remote monitoring of appliance or system output or status. 
     In this exemplary embodiment of the WLAN  400 , the data sink  416  is a high definition television (HDTV). A white space LTE transceiver  420  associated with the HDTV  416  may be a stand-alone device, or connected to or incorporated into, for example, a television set-top box of any type, a DVD or a Blu-Ray player, or any other HDTV adjunct or controller. By way of example, the white space LTE transceiver  420 , or the component to which it is connected, is connected to the HDTV by a High-Definition Multi-media Interface (HDMI). Any other suitable type of interface may also be used. The type of interface between the LTE transceiver  420  and the HDTV has no effect on the operation of the invention. The white space LTE transceiver  420  is provisioned with a frame processor  421 . The frame processor  421  inspects received LTE radio frames for control data and source data addressed to the HDTV  416 , as will be explained below in more detail with reference to  FIGS. 5 and 6 . The white space LTE transceiver  420  also has a channel estimator  423 , which performs channel estimation, as will be explained below with reference to  FIGS. 8-15 . The white space LTE transceiver  420  is also equipped with a white space LTE Tx/Rx antenna  422  that provides a wireless link  433  to the WLAN gateway  400 . The white space LTE Tx/Rx antenna  422  receives LTE radio frames transmitted by the WLAN gate  402  over the wireless link  433 . The white space LTE transceiver  420  transmits source data requests to the WLAN gateway  402  over the wireless link  433  using LTE uplink frames (not shown), the description of which is not within the scope of this invention. 
     The HDTV  416  may be controlled directly by a remote control device  424 , well known in the art. The HDTV  416  may also be controlled by any appropriate LTE-enabled device  426  (cellular telephone, PDA or the like) programmed to transmit control data (channel selection, volume control, input selection, on/off commands, etc.) to the white space LTE transceiver  420  via the white space LTE Tx/Rx antenna  414  of the WLAN gateway  402  using LTE uplink frames  440 , the description of the which is not within the scope of this invention. 
     The data sink  418  may be any computer, HDTV, appliance device or sensor, as defined above. A white space LTE transceiver or receiver  428  is connected to, or integrated into, the data sink  418 . The LTE transceiver/receiver  428  is equipped with a frame processor  429 . The frame processor  429  inspects received LTE frames for source data and/or control data addressed to the data sink  418 , as will be explained below in more detail with reference to  FIGS. 5 and 6 . The LTE transceiver/receiver  428  is also provisioned with a channel estimator  431 , which performs channel estimation, as will be explained below with reference to  FIGS. 8-15 . A white space LTE Tx/Rx or Rx only antenna  430  provides a wireless link  432  to the WLAN gateway  402 . If the white space LTE transceiver/receiver  428  can process source data, it transmits source data requests to the WLAN gateway  402  over the wireless link  432  using LTE uplink frames, the description of which is not within the scope of this invention 
       FIG. 5  is a flow diagram presenting a high-level overview of some of the functions performed on startup and downlink frame processing by the WLAN gateway  402  shown in  FIG. 4 . On startup, as described above, the spectrum sensing unit  406  scans the TV band spectrum ( 500 ) to detect unused spectrum in the predefined TV white space. The scan may be delimited by reference to a table or a database (not shown) that provides a list of channels that have been assigned to other TV white space services operating within a geographic area in which the WLAN  400  is located. After the TV band spectrum scan is complete the spectrum sensing unit  406  passes information about the scan to the spectrum manager  400  (see  FIG. 1 ). In accordance with one embodiment of the invention, the spectrum sensing manager searches the scan information for a minimum of 5 MHz unused TV white space spectrum, but any other suitable piece of vacant white space spectrum can also be used. If a piece of vacant white space spectrum of a desired bandwidth is detected ( 502 ), information about that piece of white space spectrum is passed by the spectrum manager  410  to the LTE white space transceiver  412 , as described above with reference to  FIG. 4 . After information about the available white space spectrum has been passed to the white space LTE transceiver  412 , the WLAN gateway  402  begins the execution of an endless operation loop that terminates only when the WLAN gateway  402  is switched off. 
     In a first step of the endless operation loop, the WLAN gateway  402  determines whether there is a pending or unfulfilled source data request ( 506 ) received from any of the data sinks  416 ,  418  in the WLAN  400 . If a pending or unfulfilled source data request exists, the required source data is captured ( 508 ) from an appropriate data source  404 . The source data is then processed ( 510 ) by the frame processor  413  as required (demodulated and reformatted, for example) and inserted ( 512 ) by the frame processor  413  into a LTE downlink frame in accordance with the invention. The WLAN gateway  402  then determines ( 514 ) whether it has control data to transmit. If so, the frame processor  413  inserts ( 516 ) the control data into a predetermined subset of pilot positions in the modified LTE frame, as will be explained below with reference to  FIG. 7 . The WLAN gateway  402  then transmits ( 518 ) the LTE frame. If it is determined at  506  that no unfulfilled or pending source data request exists, the WLAN gateway  402  determines whether there is control data to transmit ( 514 ). If so, steps  516  and  518  are performed as described above. If there is no control data to transmit, an LTE frame containing idle cells is transmitted at  518 . 
       FIG. 6  is a flow diagram presenting a high-level overview of some of the actions performed by the white space LTE transceivers/receivers  420 ,  428  shown in  FIG. 4  during startup and frame processing. On startup the LTE transceiver/receiver scans ( 600 ) the TV band spectrum to identify TV white space transmission channel(s) currently being used by the WLAN gateway  402 , using methods well known in the art. Once the TV white space channel(s) have been identified, the LTE transceiver/receiver begins an endless operational loop that continues until the scheduled task is completed. In a first step of the endless operational loop, the LTE transceiver/receiver receives and demodulates ( 602 ) the next transmitted LTE frame. The frame processor  421 ,  429  then inspects ( 604 ) a predefined subset of the pilot positions in the LTE frame to determine if the LTE frame carries control data. If control data exists there will be some identifier (address) in the control data to indicate its intended receiver. Consequently, the LTE transceiver/receiver tests ( 606 ) for an address match. The implementation of the address and the address match test is a matter of design choice. If there is an address match, the control data is passed ( 608 ) to a control data handler. If there is not an address match, the process proceeds to optional process  610 , or loops back to  602 . 
     Any given transceiver/receiver in the WLAN  400  may or may not be configured to process source data. Some transceivers/receivers, such as household appliances, etc. may only be configured to process control data. If the transceiver/receiver is configured to process source data, the frame processor  421 ,  429  inspects ( 610 ) the LTE frame for source data. If source data is present, the frame processor  421 ,  429  extracts the source data from the LTE frame. The frame processor then performs a source data address match test ( 612 ). As understood by those skilled in the art, the source data is delivered in internet protocol (IP) packets, the addressing of which is well known in the art. If it is determined that a source data address match exists, the source data is passed to a source data handler ( 614 ) and the process loops back to  602 . Likewise, if as determined at  610  that the frame does not contain a source data packet, or it is determined at  612  that the source data address does not match that of the data sink  420 ,  428 , the process loops back to  602 . 
       FIG. 7  is a schematic diagram of a proportion of the pilot symbols transmitted in the modified LTE downlink frame in accordance with the invention, showing released pilot symbol positions  700  used for control data transmission in the WLAN  400 . As explained above with reference to  FIG. 3 , the LTE system architecture provides a very robust downlink structure designed to provide excellent QoS to highly mobile user devices. In the WLAN  400  environment, the wireless channel can be characterized as a slowly time-varying channel. Experimentation has established that the frequency and spacing of channel estimations in the standard LTE pilot (reference) symbol structure displays redundancy that can be exploited to enhance performance within the WLAN  400 . A predetermined subset  700  of at least one half of the pilot positions  120  can be used to carry control data without adversely affecting QoS in the WLAN  400 . To ensure a high level of QoS in the WLAN  400 , channel estimation interpolation is performed in the frequency domain and the time domain to provide a channel estimate at each received symbol position in the modified LTE downlink frame, so that the predetermined subset of the pilot positions  700  can carry the control data. 
       FIG. 8  is a schematic diagram illustrating a first step in one method of interpolating channel estimates using the LTE downlink frame structure in accordance with the invention. In a first step of this method, channel estimates  801 ,  804  are computed for each existing pilot symbol in an LTE downlink frame received by an LTE transceiver/receiver in accordance with the invention. The channel estimates  804  in the 4 th  symbol position are then interleaved with the channel estimates  801  in the 1 st  symbol position, as shown in  FIG. 8 . 
       FIG. 9  is a schematic diagram illustrating the results of a second step in the method of interpolating channel estimates shown in  FIG. 8 . In the second step, interpolation is performed in the frequency domain between the interleaved channel estimates. The interpolation in the frequency domain may be performed using, for example: a linear interpolation between channel estimates; a quadratic interpolation between channel estimates; or a spline interpolation between channel estimates, all of which are known in the art. 
       FIG. 10  is a schematic diagram illustrating a third step in the method of interpolating channel estimates shown in  FIG. 8 . After the channel estimates  801  are interleaved with the channel estimates  804  and the interpolation in the frequency domain has been completed, an interpolation in the time domain is performed to complete the channel estimate computations. The interpolation in the time domain may be performed using, for example: polynomial interpolation such as cubic spline interpolation between channel estimates, which is also known in the art. 
       FIG. 11  is a schematic diagram illustrating two results  810 ,  812  of the third step of the method of interpolating channel estimates in the time domain shown in  FIG. 10  using linear, polynomial or cubic spline interpolation between frequency domain interpolations performed in the second step of this method. Although time domain interpolation is performed for all sub-carriers, and for the duration in time of the entire frame, for simplicity of illustration only the time domain interpolation for one sub-carrier in two time slots is shown. 
       FIG. 12  is a schematic diagram illustrating interpolation of channel estimates in the time domain using linear interpolation between computed (E) or frequency domain interpolated (I) channel estimates. The linear interpolation is performed using the known equation: 
     
       
         
           
             
               
                 
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     where: ĥ j (n k−1 ), ĥ j (n k ) represent the computed (E) or frequency domain interpolated (1) channel estimates as illustrated in  FIG. 9 . ĥ j (n) represents the time domain interpolated channel estimates  810  computed using the above linear interpolation formula at positions illustrated in  FIG. 11 . j=1, . . . , L, and L is the number of sub-carriers in the LTE frame. 
       FIG. 13  is a schematic diagram illustrating interpolation of channel estimates in the time domain using cubic spline interpolation between computed and interpolated frequency domain channel estimates. The cubic spline interpolation is performed using the known equations: 
         ĥ   j ( n )= a   k−1 ( n−n   k−1 ) 3   +b   k−1 ( n−n   k−1 ) 2   +c   k−1 ( n−n   k−1 )+ d   k−1   ; n   k−1   i≦n&lt;n   k    
       and 
         ĥ   j ( n )= a   k ( n−n   k ) 3   +b   k ( n−n   k ) 2   +c   k ( n−n   k )+ d   k   ;n   k   ≦n&lt;n   k+1 . 
     where: j=1, . . . , L, and L is the number of sub-carriers in the LTE frame. 
       FIG. 14  is a schematic diagram illustrating a first step in another method of interpolating channel estimates using the modified LTE downlink frame structure in accordance with the invention, and the results of the first step in this method. In accordance with this method, interpolation in the frequency domain is performed without interleaving the channel estimates in the 4 th  character position with those in the 1 st  character position. Consequently, the channel estimates are computed at their transmitted pilot symbol positions. As noted above, the interpolation in the frequency domain can be performed using any known method, for example a polynomial interpolation such as cubic spline interpolation between channel estimates. 
       FIG. 15  is a schematic diagram illustrating the results of a second step of the method shown in  FIG. 14 , in which the channel estimates are interpolated in the time domain. Although time domain interpolation is performed for all sub-carriers, and for the duration in time of the entire frame, for simplicity of illustration only the time domain interpolation for one sub-carrier in two time slots is shown. In the first time slot, the interpolations  816  and  818  are computed. In the second time slot, the interpolations  820  and  822  are computed. As noted above, the interpolation in the time domain can be performed using any one of: linear interpolation between channel estimates; polynomial interpolation between channel estimates; or, cubic spline interpolation between channel estimates. 
     The embodiments of the invention described above are only intended to be exemplary of the WLAN  400 , WLAN gateway  402 , the data sinks  416 ,  418  and the modified LTE downlink frame structure in accordance with the invention, and not a complete description of every possible configuration of any one of those. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.