Abstract:
A system is provided that includes a first device and a second device. The second device is configured to communicate wirelessly with the first device. The first and second devices selectively reduce an operational range for communications before sharing a secret, the secret related to data encryption.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a non-provisional application claiming priority to U.S. Provisional Pat. App. No. 60/706,170, entitled “Close Proximity Communications Using Multi-Band OFDM”, filed on Aug. 5, 2005, and U.S. Provisional Pat. App. No. 60/699,776, entitled “Close Proximity Communications Using Multi-Band OFDM”, filed on Jul. 15, 2005, both of which are incorporated herein by reference for all purposes. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0002]     Not applicable.  
       REFERENCE TO A MICROFICHE APPENDIX  
       [0003]     Not applicable.  
       FIELD OF THE INVENTION  
       [0004]     The present disclosure is directed to communication systems, and more particularly, but not by way of limitation, to communication systems where devices encrypt/decrypt data to enhance the security of communications between the devices.  
       BACKGROUND  
       [0005]     In order for electronic devices to communicate, a wireless or wired protocol (i.e., standard) defines hardware and software parameters that enable the devices to send, receive, and interpret data. The Federal Communications Commission (FCC) has allocated different frequency ranges (spectrums) for different wireless protocols. For example, the 802.11(a) protocol provided by the Institute of Electrical and Electronics Engineers (IEEE) specifies operating in a frequency range from 4.9-5.85 GHz (part of the Unlicensed National Information Infrastructure (U-NII) band). Also, the Worldwide Interoperability of Microwave Access (WiMAX) protocol specifies operating in frequency range from 3.3-3.8 GHz and from 5.4-5.825 GHz. More recently, the Ultra Wideband (UWB) protocol specifies operating in a frequency range from 3.1-10.6 GHz. The UWB protocol is based on Multi-band Orthogonal Frequency Division Multiplexing (OFDM) and is defined by the ECMA-368 specification provided by the WiMedia Alliance.  
         [0006]     At least one application of UWB involves Wireless Universal Serial Bus (WUSB) devices (e.g., printers, scanners, external hard drives, digital cameras or other devices) that communicate with a host system. To improve the security of communications between a WUSB device and the host system, a data encryption/decryption scheme can be implemented. In a data encryption/decryption scheme, the WUSB device and the host device share a secret (e.g., a security key) that is used to encrypt data at one device and decrypt data at the other device. If the secret becomes known to other entities, the security of communications between the WUSB and the host system can be compromised. Accordingly, methods and systems that protect the integrity of the secret are desirable.  
       SUMMARY  
       [0007]     In at least some embodiments, a system is provided that includes a first device and a second device. The second device is configured to communicate wirelessly with the first device. The first and second devices selectively reduce an operational range for communications before sharing a secret.  
         [0008]     In other embodiments, a transmitter is provided that includes close proximity transmission mode logic and extended proximity transmission mode logic. The close proximity transmission mode logic selectively reduces a transmission range before transmitting an encryption key.  
         [0009]     In still other embodiments, a receiver is provided that includes close proximity communication mode logic and extended proximity communication mode logic. The close proximity communication mode logic selectively bypasses a receiver component during a close proximity communication mode.  
         [0010]     In at least some embodiments, a method is provided that includes reducing an operational range for communications between two devices. The method further comprises sharing a secret between the two devices while the operational range for communications is reduced.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     For a detailed description of various embodiments of the invention, reference will now be made to the accompanying drawings in which:  
         [0012]      FIG. 1  illustrates a system in accordance with embodiments of the disclosure;  
         [0013]      FIG. 2  illustrates a block diagram of a transmitter in accordance with embodiments of the disclosure;  
         [0014]      FIG. 3  illustrates a block diagram of a receiver in accordance with embodiments of the disclosure; and  
         [0015]      FIG. 4  illustrates a method in accordance with embodiments of the disclosure. 
     
    
     NOTATION AND NOMENCLATURE  
       [0016]     Certain terms are used throughout the following description and claims to refer to particular system components. As: one skilled in the art will appreciate, companies may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . .”. Also, the term “couple” or “couples” is intended to mean either an indirect, direct, optical or wireless electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, through an indirect electrical connection via other devices and connections, through an optical electrical connection, or through a wireless electrical connection.  
       DETAILED DESCRIPTION  
       [0017]     It should be understood at the outset that although an exemplary implementation of one embodiment of the present disclosure is illustrated below, the present system may be implemented using any number of techniques, whether currently known or in existence. The present disclosure should in no way be limited to the exemplary implementations, drawings, and techniques illustrated below, including the exemplary design and implementation illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.  
         [0018]     Electronic devices that communicate wirelessly (or via a wired connection) implement a variety of techniques to prepare, send, receive, and recover data. For example, data preparation techniques may include data scrambling, error correction coding, interleaving, data packet formatting, and/or other techniques. The data to be transmitted is converted into blocks of data (i.e., bits) transmitted as information symbols. Each information symbol is associated with a constellation of complex amplitudes.  
         [0019]     If data communication is wireless, one or more antennas “pick up” the wireless signal, after which data is recovered by sampling the received signal and decoding each information symbol. To recover data, a receiving device may implement techniques such as signal amplification, digitization, sample rate conversion, equalization, demodulation, de-interleaving, de-coding, and/or de-scrambling.  
         [0020]     In some communication systems an encryption/decryption scheme is implemented to enhance the security of communications between a transmitting device and a receiving device. Encryption/decryption schemes can be based on a secret, such as but not limited to, a security key shared by the transmitting device and the receiving device. The secret used for or related to data encryption. Embodiments of the disclosure illustrate methods and systems that protect the integrity of the secret used for encryption/decryption. Alternatively, the methods and system could protect the integrity of any type of data transmitted between two devices. In other words, the protected data does not have to be limited to a secret or security key used for encryption/decryption.  
         [0021]     Embodiments such as those disclosed herein protect the integrity of data transferred between two devices by selectively limiting communications to within a close proximity (e.g., 5-10 cm). In at least some embodiments, a host device and a peripheral device are configured for wireless communication based on the Ultra Wideband (UWB) protocol. During an initialization mode, the transceivers of the host device and the peripheral device are configured such that communication is only possible within a limited range (i.e., communication is only possible if the devices are in close proximity to each other). For example, the initialization mode can be used to securely exchange a secret between the host device and the peripheral device.  
         [0022]     After the initialization mode is complete, the host device and the peripheral device can enter a functional mode where the transceivers of the host device and the peripheral device enable communications within an extended range (i.e., communication is possible with the devices being outside the limited range). In at least some embodiments, communications during the functional mode are protected (e.g., via encryption/decryption) using the secret that was shared between the devices during in the initialization mode.  
         [0023]      FIG. 1  illustrates a system  100  in accordance with embodiments of the disclosure. As shown in  FIG. 1 , the system  100  comprises a host device  102  in communication with a peripheral device  130 . The host device  102  may comprise, for example, a server, a desktop computer, a laptop computer, a vending machine, a kiosk, or a mobile device. The peripheral device  130  may comprise, for example, a printer, a scanner, a digital camera, a smartcard reader, a biometric reader, a Personal Digital Assistant (PDA), a cellular phone, portable or other storage devices, or some other peripheral device. In at least some embodiments, the host device  102  represents another peripheral device.  
         [0024]     As shown, the host device  102  and the peripheral device  130  communicate wirelessly. For example, in some embodiments, the host device  102  and the peripheral device  130  communicate using the UWB protocol. While embodiments illustrated herein are based on the UWB protocol, the host device  102  and the peripheral device  130  are not limited to communicating using the UWB protocol and could communicate wirelessly using another protocol now known or later developed.  
         [0025]     As shown, the host device  102  comprises a processor  104  coupled to a memory  106  and a transceiver  120 . The memory  106  stores applications  110  and encryption/decryption instructions  108  for execution by the processor  104 . If the host device  102  is a computer, the applications  110  could comprise any known or future applications useful for individuals or organizations. As an example, such applications  110  could be categorized as operating systems, device drivers, databases, presentation tools, emailers, file browsers, firewalls, instant messaging, finance tools, games, word processors or other categories. Regardless of the exact nature of the applications  110 , at least some of the applications  110  are involved in communications between the host device  102  and the peripheral device  130 .  
         [0026]     To enhance the security of communications between the host device  102  and the peripheral device  130 , the encryption/decryption instructions  108  are implemented. In the case of data encryption, the encryption/decryption instructions  108  direct the processor  104  to encrypt data based on a secret. The secret could be a key that is generated randomly or could be input by a user of the host device  102  (e.g., a user could input a password or biometric reading). After successful encryption, the encrypted data could be transmitted to the peripheral device  130  or stored for later use by the host device  102 . In the case of data decryption, the encryption/decryption instructions  108  direct the processor  104  to decrypt data based on the same secret that was used to encrypt the data. If the secret is not available, data decryption fails.  
         [0027]     In at least some embodiments, data from the host device  102  is transmitted to the peripheral device  130  via the transceiver  120 . In accordance with the UWB protocol, the transceiver  120  could have a PHY layer and a data link layer which are not shown for convenience. The PHY layer and the data link layer perform several functions such as preparing, transmitting, receiving, and decoding wireless signals. In at least some embodiments, the transceiver  120  implements a modulation technique such as Multi-band Orthogonal Frequency Division Multiplexing (Multi-band OFDM).  
         [0028]     As shown, the transceiver  120  comprises initialization mode logic  122  and functional mode logic  124 . The initialization mode logic  122  causes the transceiver  120  to operate in an initialization mode that limits wireless communications between the host device  102  and other devices to within an initialization range  150 . The initialization range  150  may be between 5-10 cm although other ranges are possible.  
         [0029]     To limit the initialization range  150  when the host device  102  is transmitting data, the initialization mode logic  122  may adjust the transceiver&#39;s transmission power level, data transfer rate, error correction encoding, interleaving, or zero-padded suffix content For example, the initialization range  150  could be minimized based on reducing the transmission power level, increasing the data transfer rate, bypassing error correction encoding, bypassing interleaving and inserting random data into zero-padded suffixes prepared by the transceiver  120 .  
         [0030]     To limit the initialization range  150  when the host device  102  is receiving data, the initialization mode logic  122  may adjust the transceivers low-noise amplification, de-interleaving, error correction decoding, or overlap-and-add operations. For example, the initialization range  150  could be minimized based on selecting low-noise amplification with a poor noise factor, bypassing de-interleaving, bypassing error correction decoding, or disabling overlap-and-add operations.  
         [0031]     One potential purpose for the limited initialization range  150  is to enable the host device  102  and another device (e.g., the peripheral device  130 ) to securely exchange data. For example, the host device  102  and the peripheral device  130  may exchange a secret that is later the basis for secure communications (e.g., data encryption/decryption) between the host device  102  and the peripheral device  130 . By limiting the initialization range  150  appropriately, maleficent entities are unlikely to capture the secret exchanged during the initialization mode (at least not without a user of the host device  102  noticing) since the entities would have to be in very close proximity. Accordingly, a presumably secure communication session between the host device  102  and the peripheral device  130  can be established based on the secret.  
         [0032]     The functional mode logic  124  causes the transceiver  120  to operate in a functional mode that extends wireless communications between the host device  102  and other devices (e.g., the peripheral device  130 ) to a functional range  160 . In some embodiments, the functional range  160  may be up to 10 meters although other ranges are possible.  
         [0033]     To extend the functional range  160  when the host device  102  is transmitting data, the functional mode logic  124  may adjust a transceivers transmission power level, data transfer rate, error correction encoding, interleaving, or zero-padded suffix content. For example, the functional range  160  could be maximized based on increasing the transmission power level, decreasing the data transfer rate, using error. correction encoding, using interleaving, and inserting zeros into zero-padded suffixes prepared by the transceiver  120 .  
         [0034]     To extend the functional range  160  when the host device  102  is receiving data, the functional mode logic  124  may adjust the transceiver&#39;s low-noise amplification, de-interleaving, error correction decoding or overlap-and-add operations. For example, the functional range  160  could be maximized based on selecting low-noise amplification with a good noise factor, using de-interleaving, using error correction decoding and enabling overlap-and-add operations.  
         [0035]     The purpose of the functional range  160  is to enable the host device  102  and another device (e.g., the peripheral device  130 ) to communicate within an extended range (within a home, office, or public location). In at least some embodiments, communications in the functional mode are encrypted/decrypted using the secret that was exchanged in the initialization mode.  
         [0036]     As shown in  FIG. 1 , the peripheral device  130  comprises a processor  134  coupled to a memory  136  and a transceiver  140 . The memory  136  stores applications  140  and encryption/decryption instructions  138  for execution by the processor  134 . The applications  140  could comprise any known or future applications related to operations of the peripheral device  134 . Regardless of the exact nature of the applications  140 , at least some of the applications  140  are involved in communications between the host device  102  and the peripheral device  130 .  
         [0037]     To enhance the security of communications between the host device  102  and the peripheral device  130 , the encryption/decryption instructions  138  are implemented. In the case of data encryption, the encryption/decryption instructions  138  direct the processor  134  to encrypt data based on a secret. As previously mentioned, the secret could be generated randomly or could be input by a user of the host device  102  (e.g., a user could input a password or biometric reading). If the secret is generated by or input to the host device  102 , the secret can be transferred to the peripheral device  130  during the initialization mode. Once the secret is successfully transferred to the peripheral device  130 , the secret can be used for data encryption/decryption. Data encrypted using the secret could be transmitted to the host device  102  or stored for later use by the peripheral device  130 . In the case of data decryption, the encryption/decryption instructions  138  direct the processor  134  to decrypt data based on the same secret that was used to encrypt the data. If the secret is not available, data decryption fails.  
         [0038]     In at least some embodiments, data from the peripheral device  130  is transmitted to the host device  102  via the transceiver  140 . Similar to the transceiver  120  of the host device  102 , the transceiver  140  may operate in accordance with the UWB protocol and may have a PHY layer and a data link layer which are not shown for convenience. The PHY layer and the data link layer perform several functions such as preparing, transmitting, receiving, and decoding wireless signals. In at least some embodiments, the transceiver  140  implements a modulation technique such as Multi-band Orthogonal Frequency Division Multiplexing (Multi-band OFDM).  
         [0039]     As shown, the transceiver  140  comprises initialization mode logic  142  and functional mode logic  144 . The initialization mode logic  142  causes the transceiver  140  to operate in an initialization mode that limits wireless communications between the peripheral device  130  and other devices to within an initialization range  150 . As previously mentioned, the host device&#39;s transceiver  120  can also operate in an initialization mode. Accordingly, the initialization range  150  can be affected by the initialization mode logic  122  of the host device  102 , the initialization mode logic  142  of the peripheral device  130 , or both. Again, the initialization range  150  may be between 5-10 cm although other ranges are possible. Likewise, the functional range  160  can be affected by the functional mode logic  124  of the host device  102 , the functional mode logic  144  of the peripheral device  130 , or both. Again, the functional range  160  may be up to 10 meters although other ranges are possible.  
         [0040]     To limit the initialization range  150  when the peripheral device  130  is transmitting data, the initialization mode logic  142  may adjust the transceivers transmission power level, data transfer rate, error correction encoding, interleaving, or zero-padded suffix content. For example, the initialization range  150  could be minimized based on reducing the transmission power level, increasing the data transfer rate, bypassing error correction encoding, bypassing interleaving, and inserting random data into zero-padded suffixes prepared by the transceiver  140 .  
         [0041]     To limit the initialization range  150  when the peripheral device  130  is receiving data, the initialization mode logic  142  may adjust the transceiver&#39;s low-noise amplification, de-interleaving, error correction decoding, or overlap-and-add operations. For example, the initialization range  150  could be minimized based on selecting low-noise amplification with a poor noise factor, bypassing de-interleaving, bypassing error correction decoding and disabling overlap-and-add operations.  
         [0042]     The functional mode logic  144  causes the transceiver  140  to operate in a functional mode that extends wireless communications between the peripheral device  130  and other devices (e.g., the host device  102 ) to a functional range  160 . In some embodiments, the functional range  160  may be up to 10 meters although other ranges are possible.  
         [0043]     To extend the functional range  160  when the peripheral device  130  is transmitting data, the functional mode logic  144  may adjust the transceiver&#39;s transmission power level, data transfer rate, error correction encoding, interleaving, or zero-padded suffix content. For example, the functional range  160  could be maximized based on increasing the transmission power level, decreasing the data transfer rate, using error correction encoding, using interleaving and inserting zeros into zero-padded suffixes prepared by the transceiver  140 .  
         [0044]     To extend the functional range  160  when the peripheral device  130  is receiving data, the functional mode logic  144  may adjust the transceiver&#39;s low-noise amplification, de-interleaving, error correction decoding or overlap-and-add operations. For example, the functional range  160  could be maximized based on selecting low-noise amplification with a good noise factor, using de-interleaving, using error correction decoding and enabling the overlap-and-add operations.  
         [0045]     In at least some embodiments, other peripheral devices (in addition to the peripheral device  130 ) could be associated with and communicate with the host device  102 . In such case, each peripheral device could exchange a secret with the host device  102  during separate initialization modes. Each initialization mode would involve placing a corresponding peripheral device within the initialization range  150  as described previously. The secret for each peripheral device enables secure communications (e.g., data encryption/decryption) between the host device  102  and the peripheral devices. To organize secure communications with multiple peripheral devices, the host device  102  may store a table (or other data format) that tracks which peripheral devices have been associated with the host device  102  as well as any secrets corresponding to each peripheral device.  
         [0046]     If the host device  102  needs to transmit data to a particular peripheral device, the host device  102  identifies the particular peripheral device and/or identifies the secret that corresponds to the particular peripheral device (e.g., by searching the table). The host device  102  can then encrypt data using the secret that corresponds to that particular peripheral device and transmit the encrypted data. Presumably, only the intended recipient of the encrypted data is able to decrypt the data. When the host device  102  receives encrypted data from the peripheral devices, the host device  102  identifies the source of the encrypted data and/or identifies the secret needed to decrypt the data (e.g. by searching the table). If the host device  102  receives encrypted data and is unable to identify a corresponding peripheral device and/or a corresponding secret, the host device is unable to decrypt the encrypted data.  
         [0047]      FIG. 2  illustrates a transmitter  200  in accordance with embodiments of the disclosure. The transmitter  200  can be implemented, for example, by the transceivers described previously for the host device  102  and the peripheral device  130 . As shown in  FIG. 2 , the transmitter  200  comprises a scrambler block  202  that receives input data. If the device implementing the transmitter  200  is operating in the initialization mode as previously described, the input data may comprise a secret to be exchanged between a host device and a peripheral device. If the device implementing the transmitter  200  is operating in the functional mode as previously described, the input data may comprise data that has been encrypted using a secret exchanged during the initialization mode.  
         [0048]     The scrambler block  202  outputs scrambled data to a multiplexer (“mux”)  230 A which either forwards the scrambled data to a convolutional encoder block  204  and a puncturer block  206  or bypasses the convolutional encoder block  204  and the puncturer block  206 . The convolutional encoder block  204  and the puncturer block  206  provide error correction encoding for the transmitter  200 . Another mux  232 A receives the output of the mux  230 A and the output of the puncturer block  206  and forwards one of these outputs. Accordingly, the error correction encoding provided by the convolutional encoder block  204  and the puncturer block  206  can be selectively bypassed based on the control signals (“CTL1” and “CTL2”) for the muxes  230 A and  232 A. In at least some embodiments, the CTL 1  and CTL 2  signals direct the muxes  230 A and  232 A to bypass the convolutional encoder block  204  and the puncturer block  206  during an initialization mode of a host device or a peripheral device that implements the transmitter  200 . Also, the CTL 1  and CTL 2  signals may direct the muxes  230 A and  232 A to utilize the convolutional encoder block  204  and the puncturer block  206 : during a functional mode of a host device or a peripheral device that implements the transmitter  200 .  
         [0049]     As shown, another mux  230 B receives the output from the mux  232 A. The mux  230 B either forwards:data to an interleaver block  208  or bypasses the interleaver block  208 . In at least some embodiments, the interleaver block  208  comprises a six symbol OFDM interleaver although other interleavers could be used. Another mux  232 B receives the output from the mux  230 B and the output from the interleaver block  208  and forwards one of these outputs. Accordingly, the interleaving provided by the interleaver block  208  ran be selectively bypassed based on the control signals (“CTL3” and “CTL4”) for the muxes  230 B and  232 B. In at least some embodiments, the CTL 3  and CTL 4  signals direct the muxes  230 B and  232 B to bypass the interleaver block  208  during an initialization mode of a host device or a peripheral device that implements the transmitter  200 . Also, the CTL 3  and CTL 4  signals may direct the muxes  230 B and  232 B to utilize the interleaver block  208  during a functional mode of a host device or a peripheral device that implements the transmitter  200 .  
         [0050]     The output of the mux  232 B is provided to a constellation mapping block  210  which converts bits into complex constellation points. In at least some embodiments the data transfer rate of the transmitter  200  can be controlled by adjusting the number of tones per bit that the constellation mapping block  210  will map. As shown, a control signal (“CTL5”) is provided to the constellation mapping block  210  for selecting the number of tones per bit. In at least some embodiments, the CTL 5  signal directs the constellation mapping block  210  to map one tone per bit during an initialization mode of a host device or a peripheral device that implements the transmitter  200 . Also, the CTL 5  signal may direct the constellation mapping block  210  to map two or more tones per bit during a functional mode of a host device or a peripheral device that implements the transmitter  200 . Stated another way, the control signal CTL 5  may direct the constellation mapping block  210  to increase the data transfer rate during the initialization mode and to decrease the data transfer rate during the functional mode.  
         [0051]     The data transfer rate of the transmitter  200  could also be affected by implementing different puncturer blocks (in addition to the puncturer block  206 ). The different puncterer blocks could be bypassed or selected using muxes controlled by control signals. In such embodiments, the control signals could direct the muxes to select a puncturer that increases the data transfer rate during the initialization mode of a host device or a peripheral device that implements the transmitter  200 . Also, the control signals could direct the muxes to select a puncturer that decreases the data transfer rate during the functional mode of a host device or a peripheral device that implements the transmitter  200 .  
         [0052]     The data transfer rate could also be affected based on time-domain spreading and frequency-domain spreading which may, for example, be implemented between the interleaver block  208  and the constellation mapping block  210 . In time-domain spreading, each symbol is effectively transmitted twice (i.e., an original symbol is transmitted, then a permutated symbol of the original symbol is transmitted). In frequency-domain spreading, data is effectively repeated twice (i.e. the same information is placed on both the lower half of the frequencies and the upper half of the frequencies). During the initialization mode, a control signal could increase the data transfer rate by decreasing the order of time-domain spreading and/or frequency-domain spreading from two to one. During the functional mode, a control signal could decrease the data transfer rate by increasing the order of time-domain spreading and/or frequency-domain spreading from one to two.  
         [0053]     The output of the constellation mapping block  210  is provided to an Inverse Fast Fourier Transform (IFFT) block  212  which performs an inverse FFT function. The IFFT block  212  may also perform other functions such as inserting pilots, adding cyclic prefixes (CPs), adding zero-padded suffixes (ZPSs) or adding guard intervals (GIs). In at least some embodiments, the IFFT block  212  selectively inserts random data into zero-padded suffixes based on a control signal (“CTL6”). For example, the CTL 6  signal may direct the IFFT block  212  to insert random data (zeros, ones, or complex numbers) into zero-padded suffixes during an initialization mode of a host device or a peripheral device that implements the transmitter  200 . Also, the CTL 6  signal may direct the IFFT block  212  to insert zeros into zero-padded suffixes during a functional mode of a host device or a peripheral device that implements the transmitter  200 .  
         [0054]     In at least some embodiments, the random data inserted into the zero-padded suffixes can be generated as a specified pseudo-noise (PN) sequence or as the output of an encryption engine that uses a private key. In this manner, a maleficent entity is unable to generate some arbitrary random data and dupe a receiving device.  
         [0055]     The output of the IFFT block  212  is received by a digital-to-analog converter (DAC)  214  which converts digital data to an analog signal. The analog signal output from the DAC  214  is provided to a multiplier  216  which multiples the analog signal by a signal “exp(j2πf c t)” from a time-frequency kernel  218 . The output of the multiplier  216  is provided to a transmitter power level block  220  that selectively controls a transmission power level based on a control signal (“CTL7”). In at least some embodiments, the CTL 7  signal directs the transmitter power level block  220  to decrease the transmission power level during an initialization mode of a host device or a peripheral device that implements the transmitter  200 . Also, the CTL 7  signal may direct the transmitter power level block  220  to increase the transmission power level during a functional mode of a host device or a peripheral device that implements the transmitter  200 . The output of the transmitter power level block  220  is received by an antenna  222  which propagates a wireless signal.  
         [0056]      FIG. 3  illustrates a receiver  300  in accordance with embodiments of the disclosure. The receiver  300  can be implemented, for example, by the transceivers described previously for the host device  102  and the peripheral device  130 . As shown in  FIG. 3 , the receiver  300  comprises an antenna  302  that receives or “picks up” a wireless signal. The received: signal is input to a pre-select filter  304  which filters the signal and outputs the filtered signal to a mux  340 A. The mux  340 A either forwards the filtered signal to a Low-Noise Amplifier (LNA)  306  having a first noise factor (NF) or to a LNA  308  having a second NF where the first NF is superior to the second NF. As an example, the first NF may correspond to a 3 to 6 dB NF and the second NF may correspond to a 16 to 28 dB NF. Another mux  242 A receives the outputs from the LNA  306  and the LNA  308  and forwards one of these outputs. Accordingly, different quality amplifications provided by the LNA  306  and the LNA  308  can be selected based on the control signals (“CTL1” and “CTL2”) for the muxes  340 A and  342 A. In at least some embodiments, the CTL 1  and CTL 2  signals direct the muxes  340 A and  342 A to select the LNA  308  (the lower quality LNA) during an initialization mode of a host device or a peripheral device that implements the receiver  300 . Also, the control signals CTL 1  and CTL 2 : may direct the muxes  340 A and  342 A to select the LNA  306  (the higher quality LNA) during a functional mode of a host device or a peripheral device that implements the receiver  300 .  
         [0057]     In alternative embodiments, a LNA that is capable of providing both a good NF and a poor NF could be implemented in place of the LNAs  306  and  308 . In such case, a control signal could direct the LNA to provide a poor NF during an initialization mode of a host device or a peripheral device that implements the receiver  300 . Also, the control signal could direct the LNA to provide a good NF during a functional mode of a host device or a peripheral device that implements the receiver  300 .  
         [0058]     The output from the mux  342 A is provided to two multipliers  310  and  312 . The multiplier  310  multiplies the output of the mux  342 A by a cosine signal “cos(2πf c t)”. The output from the multiplier  310  is input to a low-pass filter (LPF)  316 A, then a variable gain amplifier (VGA)  318 A, then an analog-to-digital converter (ADC)  320 A. The output of the ADC  320 A is provided to an amplifier gain control (AGC) block  322  which provides an amplifier gain control signal. In at least some embodiments, this amplifier gain control signal affects the LNAs  306  and  308  and/or the variable gain amplifiers  318 A and  318 B.  
         [0059]     The multiplier  312  (sometimes referred to as a “mixer”) multiplies the output of the mux  342 A by a sine signal “sin(2πf c t)” provided by a time-frequency kernel  314 . The output from the multiplier  312  is input to a low-pass filter (LPF)  316 B, then a variable gain amplifier (VGA)  318 B, then an analog-to-digital converter (ADC)  320 B. The outputs of the ADCs  320 A and  320 B are provided to a Fast Fourier Transform (FFT) block  324  which performs a FFT function. The FFT block  324  may also perform other functions such as synchronization and overlap-and-add operations. In at least some embodiments, the FFT block  324  receives a control signal (“CTL7”) that selectively enables the overlap-and-add operation. For example, the CTL 7  signal may disable the overlap-and-add operation during an initialization mode of a host device or a peripheral device that implements the receiver  300 . Also, the CTL 7  signal may enable the overlap-and-add operation during a functional mode of a host device or a peripheral device that implements the receiver  300 .  
         [0060]     The output of the FFT block  324  is provided to a frequency equalizer (FEQ) block  326  that performs frequency equalization of the received signal and removes pilots. In at least some embodiments, the FEQ block  326  functions in conjunction with a carrier-phase and time tracking block  328 . The output of the FEQ block  328  is provided to a mux  340 B that either forwards the received signal to a de-interleaver block  330  or bypasses the de-interleaver block  330 . Another mux  342 B receives the output from the mux  340 B and the output from the de-interleaver block  330  and forwards one of these outputs. Accordingly, the de-interleaving provided by the de-interleaver block  330  can be selectively bypassed based on the control signals (“CTL3” and “CTL4”) for the muxes  340 B and  342 B. In at least some embodiments, the CTL 3  and CTL 4  signals direct the muxes  340 B and  342 B to bypass the de-interleaver block  330  during an initialization mode of a host device or a peripheral device that implements the receiver  300 . Also, the CTL 3  and CTL 4  signals may direct the muxes  340 B and  342 B to utilize the de-interleaver block  330  during a functional mode of a host device or a peripheral device that implements the receiver  300 .  
         [0061]     The output of the mux  342 B is provided to another mux  340 C that either forwards the received signal to a de-puncture/decoder block  332  or bypasses the de-puncture/decoder block  332 . In at least some embodiments, the de-puncture/decoder block  332  performs forward error correction (FEC) decoding and/or dual-carrier modulation (DCM). For example, FEC could be used for data transfer rates less than or equal to 200 Mbps and DCM could be used for data transfer rates greater than or equal to 320 Mbps. In at least some embodiments, the de-puncture/decoder block  332  may implement a Viterbi decoder. As shown, another mux  342 C receives the output from the mux  340 C and the output from the de-puncture/decoder block  332  and forwards one of these outputs. Accordingly, the de-puncturing/decoding provided by the de-puncture/decoder block  332  can be selectively bypassed based on the control signals (“CTL5” and “CTL6”) for the muxes  340 C and  342 C. In at least some embodiments, the CTL 5  and CTL 6  signals direct the muxes  340 C and  342 C to bypass the de-puncture/decoder block  332  during an initialization mode of a host device or a peripheral device that implements the receiver  300 . Also, the CTL 5  and CTL 6  signals may direct the muxes  340 B and  342 B to utilize the de-puncture/decoder block  332  during a functional mode of a host device or a peripheral device that implements the receiver  300 .  
         [0062]     The output of the mux  342 C is provided to a de-scrambler  334  which descrambles the received signal. The received signal is then output from the de-scramber  334  for further processing by the recipient device. For example, if the received data is the secret (e.g., during an initialization mode), the recipient device may store the secret in a secure location and acknowledge receipt of the secret to the sender. If the received data is encrypted data (e.g., during a functional mode), the recipient device could decrypt the data based on a secret that was previously received during an initialization mode.  
         [0063]     As an example, Table 1 illustrates a “link budget” for an initialization mode. As used herein a link budget refers to a calculation of power and noise levels between a transmitter and receiver.  
                                             TABLE 1                                   Parameter   Value                                    Add White   Information Data Rate   200   Mb/s       Gaussian Noise   Average TX Power   −10.3   dBm       (AWGN) Link   Total Path Loss @20 cm   30.2   dB       Budget   Average RX Power   −40.5   dBm           Noise Power Per Bit   −91.0   dBm           CMOS RX Noise Figure   6.6   dB           Total Noise Power   −84.4   dBm           Required Eb/N0 (Uncoded)   9.6   dB           Implementation Loss   2.5   dB           Link Margin   31.8   dB           Fading Margin   3.0   dB           TX Pad (Low Attenuation +   22.0   dB           10 dB extra pad)           Intercarrier Interference   x   dB           (ICI) Loss Due           to Transmitting Random           Data In ZPS           Interleaver Loss   y   dB           Final Link Margin   6.8 − x − y   dB                   (≦0 desired)                  
 
         [0064]     As shown in Table 1, several parameters and values are suggested for determining an appropriate link budget for the initialization mode. The parameters and values represent an approximation and not intended to limit embodiments of the disclosure to any particular set of parameters or values. As shown in  FIG. 1 , a value is approximated for all parameters except unknown losses due to transmitting random data in the zero-padded suffixes (labeled “x”) and losses due to bypassing an interleaver (labeled “y”). Thus, the final link margin is estimated as 6.8−x−y dB where a final link margin that is less than or equal to 0 dB is desired.  
         [0065]     While the parameters and values of Table 1 do not necessarily illustrate preferred parameters and values, Table 1 does illustrate that some flexibility is advantageous when configuring a transmitter and receiver to function in the initialization mode. For example, perhaps only the transmitters interleaver should be bypassed and random data need not be inserted into the zero-padded suffixes. Alternatively, perhaps only random data should be inserted into the zero-padded suffixes and bypassing the transmitter&#39;s interleaver is not needed.  
         [0066]     The goal of the link budget is to achieve a close proximity communication for two devices operating in the initialization mode (i.e., the desired link budget for the initialization mode is approximately 0 dB). In at least some embodiments, selectively adjusting the features of transmitters and receivers such as the transmitter  200  (shown in  FIG. 2 ) and the receiver  300  (shown in  FIG. 3 ) should enable a close proximity initialization mode as is desired.  
         [0067]      FIG. 4  illustrates a method  400  in accordance with embodiments of the disclosure. As shown in  FIG. 4 , the method  400  comprises requesting an association between two devices (block  402 ). At block  404 , the devices exchange a secret or security key during a close proximity communication mode. In at least some embodiments, the close proximity communication mode involves adjusting features of a transmitter (e.g., a Multi-band OFDM transmitter) such as bypassing a convolutional encoder and puncturer, bypassing an interleaver, selecting a puncturer that increases a transmitter&#39;s data transfer rate, selecting a constellation mapping that increases a transmitter&#39;s data transfer rate, inserting random data into zero padded prefixes at the transmitter, or reducing a transmission power level of the transmitter.  
         [0068]     The close proximity communication mode may also involve adjusting features of a receiver (e.g., a Multi-band OFDM receiver) such as selecting a LNA having a poor noise factor, disablng an overlap-and-add operation, bypassing a de-interleaver or bypassing a de-puncturer/decoder. By adjusting the transmitter and receiver features appropriately a desired communication range (e.g., 5-10 cm) can be achieved for secure exchange of the secret during the close proximity communication mode.  
         [0069]     At block  406 , the devices communicate using the secret during an extended proximity communication mode. In at least some embodiments, the secret enables the devices to participate in a secure session where the secret is used to encrypt/decrypt data transmitted between the two devices. In at least some embodiments, the extended proximity communication mode involves adjusting features of a transmitter (e.g., a Multi-band OFDM transmitter) such as utilizing a convolutional encoder and puncturer, utilizing an interleaver, selecting a puncturer that decreases a transmitter&#39;s data transfer rate, selecting a constellation mapping that decreases a transmitter&#39;s data transfer rate, inserting zeros into zero padded prefixes at the transmitter, or increasing a transmission power level of the transmitter.  
         [0070]     The extended proximity communication mode may also involve adjusting features of a receiver (e.g., a Multi-band OFDM receiver) such as selecting a LNA having a good noise factor, enabling an overlap-and-add operation, utilizing a de-interleaver, or utilizing a de-puncturer/decoder. By adjusting the transmitter and receiver features appropriately a desired communication range (e.g., up to 10 meters) can be achieved for communications during the extended proximity communication mode.  
         [0071]     While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented  
         [0072]     Also, techniques, systems, subsystems and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as directly coupled or communicating with each other may be coupled through some interface or device, such that the items may no longer be considered directly coupled to each other but may still be indirectly coupled and in communication, whether electrically, mechanically, or otherwise with one another. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein.