Patent ID: 12261639

DETAILED DESCRIPTION

The principles of the present invention, as described in detail below, are directed to the implementation of frequency hopping in wireless communication systems in a manner that allows for the individual hops to take place across the wide (and relatively unused) frequency range available for wireless communication. A given hopping sequence is preferably generated as a random sequence, creating a unique frequency hopping map that is known by only a designated transmitter-receiver pair for an individual communication session. Applicant's previous work in the provision of frequency shifting for wireless communications (see, for example, U.S. Pat. No. 10,498,371 issued on Dec. 3, 2019 and assigned to the assignee of this invention) is based on the use of heterodyning a frequency-synthesized local oscillator (LO) and an input communication signal, and provides the basis for the application of frequency hopping, as described in detail below.

FIG.1is a simplified block diagram of an exemplary wireless transceiver10formed in accordance with the teachings of the present invention to provide frequency-hopped transmission (and reception) of wireless signals. Wireless transceiver10is shown as including a transmit section12and a receive section14.

Referring now to transmit section12of transceiver10, an input signal IF from a conventional wireless device) supplied as a first input to a mixer16, with a local oscillator (LO) signal used as the second input to mixer16. The LO signal is provided by a frequency synthesizer18that is able to generate an oscillating output operating at any desired frequency value. In accordance with the principles of the present invention and described in detail below, by virtue of using a frequency synthesizer to create the mixing signal, it is possible to provide the series of different, random LO frequencies required to perform frequency hopping on the IF input signal. Indeed, the use of a frequency synthesizer opens up the spectrum of available frequencies to be used for this purpose (e.g., anywhere within the spectrum from 10 MHz to 100,000 MHz). Alternatively, the frequency hopping may be applied to the incoming IF signal instead of the LO signal. For the sake of discussion, the hopping will be described below as used with the LO input, with the understanding that the same principles apply to the IF input.

In accordance with the principles of the present invention, a frequency controller20and a hopping sequence generator22are used in combination with LO frequency synthesizer18to perform frequency hopping on the IF input signal (or vice versa).FIG.2contains simplified diagrams illustrating the application of frequency hopping, where it is presumed in this example that the LO frequency is changed for each frame that is transmitted. A hopping sequence map M1is depicted as identifying a randomly-selected LO frequency to be used as an input to mixer16. In particular, M1shows the relationship between the frame of the IF input message and the LO frequency to be used for that frame. A graph depicting this use of different LO frequencies as a function of time is also shown inFIG.2, illustrating the “hopping” of the transmitted frames from using one frequency to the next.

It is also possible that further randomness may be added to the transmission by also changing the LO frequency at random points in time instead of the per-frame arrangement as shown in map M1. For example, map RM inFIG.2illustrates this use of a random “dwell time” for each LO frequency (dwell time measured in this case as a function of the number of frames to be transmitted using the same LO frequency). In general, as long as a paired transmitter and receiver are utilizing the same hopping sequence map, the receive is able to accurately recover the transmitted signal (the frequency hopping reducing transmission errors associated with noise and/or poor signal quality at certain frequencies, as well as frustrating unwanted third parties from accessing the transmitted message).

Returning to the description of wireless transceiver10ofFIG.1, hopping sequence generator22of transmit section12is used to create a hopping sequence map, such as map M1shown inFIG.2, of a random selection of LO frequencies to be used. Hopping sequence generator supplies the sequence of randomly-generated specific frequency values to frequency controller20. In turn, frequency controller20sends an instruction to frequency synthesizer18to create the “next” LO frequency to be used as an input to mixer16.

As a result of changing the LO frequency (perhaps on a frame-by-frame basis or, alternatively, on a random basis as illustrated by map RM ofFIG.2), the center frequency of the RF output from mixer16changes as well.

In order for a band-limited output signal to be created by transmit section12, a bandpass filter24is shown as positioned at the output of mixer16. Moreover, bandpass filter24must be a tunable device having an adjustable center frequency that spans the possible frequency spectrum that may be generated by frequency hopping. Therefore, as shown inFIG.1, frequency controller20also provides the frequency values associated with map M1as an input to bandpass filter24so that its center frequency will track with the changes produced by frequency synthesizer18. A control output from frequency controller20is also applied to antenna system26, so that tuning may take place prior to the RF transmission of the frequency-hopped version of the original input signal.

As will be discussed below in association withFIG.3, a remotely-located receiver needs to utilize this same frequency hopping map M1in order to properly recover the original data signal from the received frequency-hopped RF signal.

Continuing with the discussion ofFIG.1, receive portion14of wireless transceiver10functions in a manner similar transmit section12so as to be able to convert a frequency-hopped received signal back into a recovered baseband signal. The incoming signal is first captured by antenna system26and converted into an electrical version. The received signal is then applied as an input to a low noise amplifier (LNA)30to preferentially boost the power of the current center frequency (that is, associated with the relevant frequency hopping sequence) with respect to any other spurious signal (noise) outside of small band surrounding Rin(i.e., improving the signal-to-noise ratio for the received signal, which is typically of relatively low power).

The output from LNA30is then applied as a first input to a mixer32, with a second input to mixer32being a frequency synthesizer34. In the exemplary embodiment ofFIG.1, a frequency controller36is included in receive portion14of wireless transceiver10and is used to send instructions to frequency synthesizer34with respect to the sequence of frequency values to be used as the LO input. For proper operation of receive section14, the receive signal path must use the same frequency hopping sequence map that is used by a remotely-located transmitter (not shown) to create the frequency-hopped message in the first place. For the purposes of discussion, it will be presumed that a hopping sequence map M2was used by the remote transmitter. There are various ways that hopping sequence map M2may be provided to receive portion14, as will be discussed in detail below. For present purposes, frequency hopping sequence map M2is merely shown inFIG.1as applied as an input to frequency controller36.

Applying the same logic as discussed above in association with transmit portion12, the particular hopping sequence map M2used in receive portion14needs to control the operation of LNA30, so that the primary frequency being amplified properly tracks the hopping sequence. Similarly, antenna26needs to be continuously tuned to receive the proper frequency as well.

It is to be recalled that previous implementations of FHSS systems were somewhat limited by the expense and complexities associated with the ability to handle multiple frequencies. Here, however, by implementing frequency hopping through the use of frequency synthesizers18,34, a configuration is provided that allows for frequency hopping over a wide frequency range to be implemented in a system without extremes in additional cost or complexity. Indeed, it is contemplated that a frequency range spanning between 10 MHz and 100,000 MHz may be used as a source for randomly-selected LO frequency hopping values.

As mentioned above, in order for a frequency-hopped transmission to be properly recovered, the receiver needs to follow the same hopping sequence as used by the transmitter.FIG.3illustrates this process, using a pair of transceivers10, designated as “10 West” (10W) and “10 East” (10E). In this particular embodiment, transmit section12W further includes a power amplifier25W disposed beyond the output of bandpass filter24W and used to further amplify the signal in the filtered region around the defined center frequency. As with bandpass filter24W, power amplifier25W is a tunable device and controlled by frequency controller20W in order to maintain its center frequency (associated with amplification) in synch with the frequency-hopping sequence used to generate the IF signal to be transmitted.

For the sake of discussion, it will be presumed that a wireless transmission is in progress between transmit section12W of transceiver10W and receive section14E of transceiver10E, the transmission based on the hopping sequence map M1as discussed above. Therefore, in order for receive section14E to properly recover this transmission, mixer32E must use the same hopping sequence as its LO input. Map M1is thus shown as the input to frequency controller36E of receive portion14E. Frequency controller36E (using map M1) tunes antenna system26E is properly receive the incoming frequency-hopped signal Sout, and also adjusts the center frequency being amplified by LNA30E.

The output from LNA30E is then applied as a first input to mixer32E, with the second input to mixer342being frequency synthesizer34E, which is controlled by instructions from frequency controller36E (again, using hopping sequence map M1). As discussed above, the map used by transmit section12W (here, map M1) has previously been communicated to receive section14E. The IF output from mixer32E then passes through bandpass filter38E to recover the transmitted message signal.

FIG.4is a block diagram illustrating an exemplary configuration that may be used to generate the random frequency hopping sequence maps that are used to control communications in accordance with the principles of the present invention.FIG.4illustrates wireless transceivers10W and10E, as discussed above in association withFIG.3. However, in this case, transmit portion12W of transceiver10W does not include a hopping sequence generator. Instead a network element40W is used to create frequency hopping sequence maps and provide them to wireless transceiver10W. Similarly, a network element40E provides frequency hopping sequence maps to wireless transceiver10E. In this example, each network elements40W and40E is shown as including a hopping sequence generator (designated as42W and42E, respectively) that creates all of the randomly-selected frequency hopping sequences to be used, with network elements40W,40E configuring the maps from this information and communicating them to transceivers10W and10E. By virtue of using a network-based component, the assurance that each randomly-generated sequence is unique. Here, network element40W is shown as providing generated map M1to transmit section12W and map M2to receive section14W. Each network element40is shown as further comprising a GPS component44, which may be used to synchronize their sequence generators42.

In some embodiments, network element40may have access to information with respect to the quality of transmission at certain frequencies, which may change over time. This information may be passed along to sequence generator42and used during the generation of a following sequence to avoid having a transmission include a “bad” frequency in the hopping sequence, the avoidance of bad LO frequencies contemplated as decreasing the chance of failed transmissions. The use of random frequency selection, as well as random dwell time (i.e., randomizing the number of frames transmitted with a particular hop frequency), in accordance with the present invention, is contemplated as increasing the resilience of the transmitted signals to jamming and/or detection by non-designated receivers.

In another implementation of providing the unique frequency hopping sequence from a transmitter to a designated receiver, the identity of the “next” frequency to be used in a defined sequence may be included within a control information portion (e.g., header) of a current frame being transmitted. This methodology is illustrated inFIG.5, which depicts the transmission of several frames in sequence (F1, F2, . . . ). The ability to transmit this frequency hopping information within the frame eliminates the need to maintain synchronization between the transmitter and receiver, or require the use of a network element to provide the frequency hopping maps.

In the particular arrangement as shown inFIG.5, it is presumed that an initial default frame F0uses a default (start-up) LO frequency. When assembling frame F0for transmission, a “next frequency” indicator in its header portion H0is set to the first frequency hop defined in map M1(i.e., f4). Thus, the following frame F1will use f4as its LO frequency. The process follows in a like manner, with header portion H1of frame F1including information for the next hop frequency; that is f1, as per map M1.

While the above discussion has referenced the use of frequency hopping in a wireless transmitter-receiver pair, it is to be understood that frequency hopping may be incorporated within any wireless transmission system that utilizes frequency shifting, such as described in several of the applicant's previously-issued patents, including the patents referenced above.

For example,FIG.6is a simplified diagram of a private network architecture60employing frequency hopping in accordance with the teachings of the present invention. A master device62, which may be at a fixed location, includes a transceiver10employing frequency hopping as described above in association withFIG.1, with the same reference numerals used to define the same elements. In this embodiment, master device62is in communication with a plurality of client devices64, with each client device having a similar frequency hopping transceiver, shown here as10c. The communications between master device62and client devices64is typically a “one-to-many” broadcast mode from the master device, with the individual client devices responding. However, it is contemplated that from time to time, various ones of client devices64may form an ad hoc mesh network to directly share communications.

The addition of frequency hopping in accordance with the principles of the present invention, therefore, relies on all of the transceivers using the same frequency hopping sequence, as supplied by a random hopping sequence generator66. In this particular arrangement master device62uses a first map MD1as its transmit hopping sequence, and therefore all of the receive sections14in client devices64must use this same map MD1to properly recover the transmitted message. In the other direction, it is presumed that all client devise64use the same transmit hopping sequence, which is defined here as following a hopping sequence map MD2. Thus, master device62is required to utilize map MD2as its receive hopping sequence map in order to properly recover transmissions from the individual client devices64. It is also possible that each individual client device64iuses its own transmit hopping sequence map (i.e., MD2i), where in that case master device62includes a plurality of receive hopping sequence maps and selects the proper map to use based on the identity of the particular client device sending a transmission.

Taken a step further, client-to-client communications may utilize yet a different frequency hopping sequence (established by a designated node in the ad hoc mesh network network).

FIG.7illustrates, again in simplified form, an N-channel MIMO transceiver70that may also use frequency hopping in accordance with the teachings of the present invention. In contrast to prior art multi-channel MIMO configurations where each channel is assigned its own (limited) frequency band to use for transmissions, the addition of frequency hopping allows for all channels to make use of the complete, wide frequency band available for wireless communication. This is considered as a significant advance, both in terms of expanding the set of frequencies available for each channel as well as improving the security of the individual communication links.

As shown inFIG.7, system70includes a plurality of N individual channels72that may be used to support MIMO communication, where each channel72iincluding a transmit section12iand a receive section14i, similar in form and function to transmit section12and receive section14as discussed above. The use of frequency hopping is illustrated in this embodiment by the presence of transmit mixers161-16Nand receive mixers321-32Nin channels721-72N, respectively. Channel721explicitly indicates the presence of transmit section121and receive section141; for the sake of clarity, the remaining channels do not particularly illustrate this detail.

In this embodiment, a transmit LO frequency synthesizer74is configured to provide a set of N separate LO frequency inputs to mixers161-16Nof transmit sections121-12N, based on commands supplied by a transmit frequency controller76. An included frequency hopping sequence generator78is shown as creating a set of transmit hopping sequence maps A1-AN that are provided to transmit frequency controller76. A separate transmit hopping sequence is utilized, as shown, as the LO input to each mixer161-16N, respectively.

A receive LO frequency synthesizer80is similarly used to provide a set of N separate LO frequency inputs to mixers321-32Nof receive sections141-14Nof channels721-72N, based on commands from receive frequency controller82. As discussed above, receive frequency controller82is supplied with hopping sequence maps B1-BN via any suitable means (e.g., directly sent from remotely-located transmitters, using next-hop information in the header portion of a received frame, supplied from a network element, etc.). Again, a separate receive hopping sequence is utilized as the LO input to each mixer321-32N.

The inclusion of frequency hopping in the MIMO context is therefore quite advantageous in that the “next frequency” is selected from over the wide frequency spectrum available for use. By virtue of opening up the possibilities of using frequency hops over such a wide range, the possibility of untoward detection (or jamming) is significantly decreased. Moreover, inasmuch as the transmit and receive portions of an individual radio may be using different hopping sequences, it becomes very difficult to “spoof” the system. Additionally, when utilized in a Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) system, the transceiver may disable its Clear Channel Assessment (CCA) in a high interference environment to avoid having its transmission being shut down. The radio can use AES256 encryption for inter-node messaging to prevent hacking. The radio can use beam steering to increase its immunity to potentially jamming of the transmission frequency by outsiders. The radio can lower the transmitter power to maintain a good link quality and high modulation rates. Reduction of transmitter power is further considered to reduce the possibility of detection. High modulation rate makes the packet transmission time short and hence reduces the possibility of detection. The radio can go into complete silence mode for a specified period of time or until it receives the wake up command to avoid detection

Summarizing, the application of frequency hopping to the previously presented frequency-shifted capability may be used in any FDD or TDD wireless system (e.g. LTE, Wi-Fi or 5G/6G). The transmitted signal may change (hop) frequencies in a random sequence through the control of included frequency synthesizers to change the LO frequency (or by changing the IF frequency from the modem). The transmitter and associated receiver synchronize the random channel map at the power up time (and perhaps periodically thereafter) to ensure that all radios in the network are using a unique sequence. The channel map includes information about the next hop frequency and perhaps the dwell time to use at the start of the next frame. Thus, the channel map eliminates the need to precisely synchronize the transmitter and the receiver of each radio in the network.

Advantageously, the “next” frequency to be used is selected from a large spectrum of a multiple bands (i.e. not limited to the current operating band). Transmission spread over a wide frequency range minimizes the probability of jamming and detection. Further, the utilization of a random next frequency and dwell time selection increases the resilience to jamming and detection, all in accordance with the principles of the present invention.

While the present invention has been described with respect to a limited number of embodiments, those skilled in the art will appreciate numerous modifications and variations that may be related thereto. It is intended that the appended claims cover all such modifications and variations so as to fall within the true spirit and scope of the present invention.