Patent Application
20080010208
To address the above-mentioned need a method and apparatus is provided for allowing communication of a secondary communication device over spectrum allocated to a primary user. During operation a replica portion of a signal transmitted by the primary user will be periodically transmitted by a device within the secondary communication system. This test signal is used to exercise the primary user detection apparatus of transceivers utilizing the secondary communication system. Transceivers will report on the reception of the replica signal. If the detection fails, transmission by the transceiver is prohibited.
The present invention encompasses a method comprising the steps of creating a replicated signal and transmitting the replicated signal to a secondary user at known time periods, causing the secondary user to either prevent or allow the secondary user to transmit within the frequency band based on whether or not the replicated signal was received by the secondary user. The replicated signal is a copy of at least a portion of a signal that is transmitted by a primary user.
The present invention additionally encompasses a method for allowing or preventing communication within a communication system. The method comprises the steps of creating a replicated signal that is transmitted by a primary user within a frequency band, transmitting the replicated signal to a secondary user operating within the frequency band, and receiving an indication from the secondary user as to whether or not the replicated signal was received by the secondary user. The secondary user us allowed to transmit within the frequency band based on whether or not the replicated signal was received by the secondary user.
The present invention additionally encompasses a method comprising the steps of determining if a replicated signal was received from a secondary user, determining if a transmission from a primary user was received, and allowing or denying transmission for a secondary user based on whether or not the replicated signal was received, and whether or not the transmission from the primary user was received.
The present invention additionally encompasses an apparatus comprising logic circuitry creating a replicated signal, wherein the replicated signal is a copy of at least a portion of a signal that is transmitted by a primary user. The apparatus additionally comprises a transmitter transmitting the replicated signal to a secondary user at known time periods, causing the secondary user to either prevent or allow the secondary user to transmit within the frequency band based on whether or not the replicated signal was received by the secondary user.
The present invention additionally encompasses an apparatus comprising logic circuitry determining if a replicated signal was received from a secondary user and determining if a transmission from a primary user was received, the logic circuitry allowing or denying transmission for a secondary user based on whether or not the replicated signal was received, and whether or not the transmission from the primary user was received.
Turning now to the drawings, wherein like numerals designate like components,
In this illustration, it is assumed that devices within communication system 120 are authorized to transmit on a particular frequency as a primary user, and that users of communication system 121 operate under authorization on a secondary basis. Under these conditions, it is imperative that users of communication system 121 not interfere with the users of communication system 120.
As shown, communication system 120 comprises video distribution device (VDD) 101 that conforms to the Advanced Television Standards Committee (ATSC) standards and to the FCC rules concerning digital televisions. VDD 101 (acting as a transmitter) communicates with television 107 using an over-the-air ATSC-conforming transmission 104 as a composite multiplex on a broadcast television channel. Communication system 120 may also comprise transmitter 116 and transceiver 118, for example, a wireless microphone system compliant with FCC Part 74 regulations and operating on a broadcast television channel. In this example, in addition to receiving signal 117 from transmitter 116, transceiver 118 also transmits a beacon 119, advertising the presence of the communication system 120 to communication system 121.
Communication system 121 comprises base station 111 transmitting data to transceiver 105 via over-the-air downlink transmission 113. Transmissions may also be sent from transceiver 105 to base station 111 via transceiver 105 transmitting uplink communication signal 106.
Secondary radio system 121 will utilize spectrum assigned to a primary system 120 using an opportunistic approach. With this approach, the secondary radio system will share the spectrum with primary incumbents as well as those operating under authorization on a secondary basis. Under these conditions, it is imperative that any user in the cognitive radio system 121 not interfere with primary users of communication system 120.
In order for system 121 to operate as a secondary user in the broadcast television spectrum, both base station 111 and transceiver 105 must perform the necessary steps to determine an available channel for secondary operation. Particularly, both base station 111 and transceiver 105 serve as means for performing whatever determination is required by the FCC rules to ensure that their transmissions will not interfere with the users of communication system 120. This may comprise having logic circuitry determine if transmissions will cause interference by analyzing a received signal, or accessing an external database, or determining that no transmissions exist on the primary channel. After both base station 111 and transceiver 105 have determined that their transmissions on a particular channel will not interfere with communication system 120, transmissions may begin using the spectrum licensed to communication system 120.
As discussed, a weakness of above technique is that a hardware or software failure within transceiver 105 can result in the non-detection of transmission 104 or beacon 119, leading to interference to the primary user. In order to address this need, a replica 114 of transmission 104 or beacon 119 (or alternatively, a portion of transmission 104 or beacon 119) is transmitted by cognitive radio system 121 and a determination is made as to whether or not transceiver 105 detects replica transmission 114. In a first embodiment, a burst of the protected digital television (DTV) pilot tone 103 is periodically inserted in a packet header. This test signal 114 is used to exercise the primary signal detection apparatus of transceiver 105. Transceiver 105 will report on the reception of signal 114. If the detection fails, transmission by transceiver 105 is prohibited.
The sample signal may be sent periodically in time (e.g., every hour), after every set number of received packets (e.g., sent in every Nth packet, where N is an integer), or some combination of both (e.g., every 100 packets, but at least once per hour). Additionally, a signal quality estimate of the inserted signal can be made and stored by base station 111, so changes over time may be monitored and gradual degradation, as opposed to outright failure, of the receiver may be detected.
Thus, in accordance with the present invention, base station 111 will duplicate a signal (or beacon) that is transmitted by the primary user within a frequency band and transmit the replicated signal to a secondary user (i.e., transceiver 105) operating within the frequency band. An indication will be received from transceiver 105 as to whether or not the replicated signal was received. Base station 111 will prevent or allow transceiver 105 to transmit within the frequency band based on whether or not the replicated signal was received by transceiver 105. In a preferred embodiment of the present invention, transceiver 105 will expect reception of replica transmission 114 as part of a message of known format sent by base station 111. Transceiver 105 will prevent or allow transceiver 105 to transmit within the frequency band based on whether or not replica transmission 114 was received by transceiver 105.
It should be noted that while base station 111 is shown with a unique antenna transmitting replica transmission 114, one of ordinary skill in the art will recognize that this need not be the case since a single antenna may be utilized for transmission of both downlink transmission 113 and replica transmission 114. Similarly, while transceiver 105 is shown with a single antenna, one of ordinary skill in the art will recognize that this need not be the case since two or more antennas may be utilized for reception of downlink transmission 113 and replica transmission 114.
It should be noted, that replica transmitter 205 is not simply a “repeater”, repeating transmissions of communication system 120. Replica transmitter 205 transmits replica signals 114 at known time intervals, regardless of what is being transmitted by communication system 120. Further, in a preferred embodiment replica signals 114 comprise signals that have similar properties to those of the primary user, but may or may not have been actually sent by the primary user. For example, replica signal 114 may comprise a 1-0 digital pattern with the same modulation format and data rate as the primary user, who of course is unlikely to send such a pattern on his own.
As discussed above, communication system 121 can operate such that transceiver 105 reports back to base station 111 on any replica signal received, having base station 111 determine whether or not to allow transceiver 105 to communicate. Alternatively (and preferably), base station 111 may simply transmit the replica signal or beacon at a known time and transceiver 105 will prevent or allow transceiver 105 to transmit within the frequency band based on whether or not replica transmission 114 was received by transceiver 105.
Continuing, at step 405 microprocessor 203 determines whether or not replica transmission 114 was received by transceiver 105 and either allows or denies transceiver 105 to communicate based on the determination (step 407). More specifically, if microprocessor 203 determines that the replica transmission 114 was not received, transceiver 105 will not be allowed to communicate via spectrum assigned to communication system 120.
As discussed above, in an alternate embodiment of the present invention transceiver 105 may report a received quality of replica transmission 114. The receive quality can be stored by base station 111, so changes over time may be monitored and gradual degradation, as opposed to outright failure, of the receiver may be detected. During this scenario, microprocessor 203 will track the receive quality of beacon signal 114 and if the quality shows degradation over time, or degradation below a threshold, transceiver 105 may be prevented from communicating via spectrum assigned to communication system 120.
While the invention has been particularly shown and described with reference to a particular embodiment, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. For example, transceiver 105 may transmit replica transmission 114, rather than base station 111, in which case transmission from base station 111 will depend upon proper reception of replica transmission 114. As a second example, to counteract the presence of fading, the decision to inhibit transmission may be made based on a number of reception results, not just one, and may consider other factors, such as a correlation value to a pseudo-noise sequence in replica transmission 114. It is intended that such changes come within the scope of the following claims.
