Patent Description:
One way to attempt to keep the signals from being detectable by other entities is to send signals using direct sequence spread spectrum (DSSS) as part of a CDMA system. For example, a transmitter may be configured to use a communication signal to modulate a pseudo-noise signal to create a DSSS signal. The pseudo-noise comprises a continuous sequence of pulses, where each pulse is referred to as a chip, and where the chip rate is the frequency of pulses. The chip rate is typically significantly higher than the symbol rate of the communication signal. This results in a signal that exists beneath the noise floor. In particular, the signal is a low probability of detection (LPD) signal that is not readily detectable without specialized detection circuitry and techniques.

Often, when signals cannot be decoded by a legitimate receiver, the sender will increase the power of the signal to increase the signal-to-noise ratio of the signal to allow the receiver to detect and decode the signal. An adversary may use this information to create a situation where the adversary can detect the signal. In particular, the adversary may use "Jam, Blank and Observe" detectors to attempt to detect the signals. A "Jam, Blank and Observe" detector sends a jamming signal, which typically causes a sender to increase signal power. The detector then blanks the jamming signal, and observes the signal being sent from the sender to the receiver at higher power before the sender has a chance to lower the power of the signal.

Document <CIT> discloses apparatus, method and software for secure short-range wireless communication.

One embodiment illustrated herein includes a method as defined in independent claim <NUM>.

Some embodiments illustrated herein use closed-loop rate control, with constant (or at least limited) power to increase signal-to-noise ratio for signals. This can be done, for example, to prevent signals from becoming detectable by an adversary.

Closed-loop rate control dynamically alters the rate of communication signals sent by a receiver in an attempt to properly balance the energy per bit received by a receiver to achieve some desired signal-to-noise ratio. This can be particularly useful in CDMA systems, when covertness is considered important. When the energy per bit perceived by the receiver is determined to deviate from a target level, the data rate of that channel is adjusted through feedback to the transmitter, thus keeping the power transmitted by the receiver constant (or at least below some predetermined threshold) while increasing the energy per bit by reducing the data rate. A "Jam, Blank and Observe" detector therefore is rendered ineffective, as a jamming signal by an adversary would simply result in a reduction of the data rate of the data signal being transmitted by the transmitter, rather than an increase in power for the data signal being transmitted by the transmitter. Thus, when the adversary blanked the jamming signal, the data signal would still not be detectable by the adversary.

Additionally, embodiments may be implemented where information about a transmitter's priorities and knowledge of the applications carried over communication links can be used to constrain the rate control algorithm to give preference to certain channels' rates over other channels.

Closed-loop rate control is a countermeasure that can be used to keep a communication link more covert on fading channels than is possible with closed-loop power control. Closed-loop rate and power control can be used together if desired to form a more comprehensive energy control function that operates with constraints not usually found in commercial systems.

Referring now to <FIG>, an example is illustrated of a point-to-point link in which it is desirable to keep the transmission covert (low probability of being detected - LPD). In particular, <FIG> illustrates an example where a transmitter <NUM> is sending a signal <NUM> intended for a receiver <NUM>. As illustrated in <FIG>, the signal <NUM> decreases in spectral flux density as the signal moves away from the transmitter <NUM>. Spectral flux density defines a rate of electromagnetic radiation at a given physical location, and is typically measured in an amount of energy per surface area, per wavelength. Spectral flux density can be conceptualized as the amount of "power" for a given wavelength of a signal, at a given location. As systems attempt to manage spectral flux density, the system will need to manage the competing goals of having a sufficient spectral flux density for the receiver <NUM> to be able to receive and decode the signal <NUM> while preventing an adversary <NUM> at a physical location <NUM> from being able to detect the signal <NUM>.

Note that the receiver <NUM> has the advantage of knowing the spreading codes used to transmit the signal <NUM> by the transmitter <NUM>, such that the receiver <NUM> can despread the signal using appropriate codes, and thus the receiver <NUM> is able to recover the signal <NUM> even when the signal <NUM> is below the noise floor in an environment. That is, as the receiver <NUM> applies despreading codes, the signal <NUM> will become detectable to the receiver <NUM> as the despreading codes cause the signal to concentrate power over a narrower spectral bandwidth, causing the signal in that spectral bandwidth to be above the noise floor, and therefore detectable by the receiver <NUM>.

In contrast, the adversary <NUM> at the physical location <NUM> will need to attempt to use specialized techniques to detect the signal below the noise floor, which would be very difficult if not impossible, or to cause the transmitter <NUM> to increase power of the signal <NUM> to cause the signal, even though spread by spread-spectrum, to be transmitted in a fashion that is more detectable by the adversary <NUM> at the physical location <NUM>.

Thus, embodiments herein attempt to transmit the signal <NUM> in a way such that the spectral flux density of the signal <NUM> remains below some predetermined threshold at a particular point. In particular, the transmitter <NUM> may have some information indicating that the adversary <NUM> exists at the physical location <NUM>, or in proximity to the physical location <NUM>. The transmitter <NUM> then transmits the signal <NUM> such that the signal <NUM> is below a predetermined spectral flux density at the physical location <NUM>. This threshold takes into account channel conditions, such as an ambient noise floor such as an average magnitude of the noise floor <NUM>, and such that an increase in the magnitude of the noise floor will not increase the threshold spectral flux density for the signal <NUM> transmitted by the transmitter <NUM>. That is, other noise whether caused by the adversary <NUM> or other sources, will not cause the transmitter <NUM> to increase the power of the signal <NUM> thereby increasing the spectral flux density of the signal <NUM> at the physical location <NUM>.

For example, reference is now made to <FIG>, which illustrates the signal <NUM> in a graph <NUM>-<NUM> showing the signal <NUM>, graphing power versus frequency, with respect to the noise floor <NUM>. When the signal <NUM> is first generated at the transmitter <NUM> or related circuitry, the signal <NUM> will be above the noise floor <NUM> and will be readily detectable by receivers or other entities. However, the transmitter <NUM> applies spreading codes <NUM> to the signal <NUM> which causes the signal <NUM> to be spectrally spread such that the signal <NUM> exists below the noise floor <NUM> as illustrated in the graph <NUM>-<NUM>. This is the state of the signal shown in <FIG> being perceived by the receiver <NUM> or adversary <NUM>. That is, generally entities will not be able to detect the signal <NUM> as it will be below the noise floor <NUM> as illustrated at the graph <NUM>-<NUM>.

However, the receiver <NUM> implements despreading codes <NUM>, which cause the signal <NUM> to have a narrower spectral bandwidth causing signal power to be concentrated within a narrower range of frequencies, causing the signal power to be above the noise floor <NUM> as illustrated in the graph <NUM>-<NUM>. Due to the fact that the receiver <NUM> is able to implement these despreading codes <NUM>, the receiver <NUM> can then receive and decode the signal <NUM>.

In contrast, the adversary <NUM> at the physical location <NUM> does not have the despreading codes, and thus does not have the ability to concentrate the power within a particular spectral bandwidth to be able to intercept the signal <NUM>. That is, the adversary <NUM> will be in an environment with the signal <NUM> that is characterized by the signal power and noise floor <NUM> illustrated in the graph <NUM>-<NUM>. Note that while the graph <NUM>-<NUM> shows the signal <NUM> below the noise floor <NUM>, conditions may occur which cause the signal <NUM>, even though the signal has been spread, to be above the noise floor <NUM>. In particular, if the transmitter <NUM> sends the signal <NUM> with sufficient power, then the signal <NUM> may be above the noise floor <NUM> even though the signal has been spread. As noted previously, an adversary may attempt to elicit this behavior by attempting to jam the signal <NUM> by transmitting additional noise signals to decrease the signal-to-noise ratio with respect to the receiver <NUM> to attempt to cause the transmitter <NUM> to increase the signal power for the signal <NUM> in hopes that the signal <NUM> will be transmitted above the noise floor <NUM> when the adversary <NUM> blanks the jamming signal to reduce the noise floor.

For example, reference is now made to <FIG> illustrates a graph <NUM>-<NUM>. In the graph <NUM>-<NUM> the noise floor <NUM> is at a level Ln1. The signal <NUM> is at a level Ls. The adversary <NUM> begins transmitting a jamming signal <NUM>. This causes the level of the noise floor <NUM> to be raised to level Ln2 as illustrated in the graph <NUM>-<NUM>. However, the transmitter <NUM> will not respond with an increase in the power of the signal <NUM>, but will rather maintain the signal <NUM> at the level Ls. Transmitting the signal at the level Ls allows the signal to be transmitted such that a particular spectral flux density is achieved at the physical location <NUM>. That spectral flux density will be the same whether the noise floor is at the level illustrated in the graph <NUM>-<NUM>, or at the level illustrated in the graph <NUM>-<NUM>.

However, to combat the increased noise from the jamming signal <NUM>, the transmitter <NUM> reduces the bit rate of the signal <NUM>. This increases the power per bit of the signal <NUM> (thereby increasing the signal-to-noise ratio) by having fewer bits received by the receiver <NUM> per period of time with the same power. This results in a spectral flux density of the signal <NUM> that does not change at the physical location <NUM> even though the signal-to-noise ratio is increased with respect to the receiver <NUM>. Thus, the transmitter <NUM> is able to transmit a signal <NUM> to the receiver <NUM> without making the signal <NUM> more visible by the adversary <NUM> at the physical location <NUM> as a result of the spectral flux density being constant, or at least below some predetermined threshold.

Referring again to <FIG>, adjusting the bit rate of the signal <NUM> is accomplished based on feedback communications between the transmitter <NUM> and the receiver <NUM>. In particular, the transmitter <NUM> sends a signal <NUM> to the receiver <NUM>. The receiver <NUM> responds with a feedback message <NUM> that identifies to the transmitter <NUM> the signal-to-noise ratio of signals received by the receiver <NUM>. The transmitter <NUM> then adjusts the bit rate of the signal <NUM> in response to the signal-to-noise ratio identified in the feedback message. This can include lowering the bit rate to increase the signal-to-noise ratio, or raising the bit rate if such actions can be performed and still be within a particular threshold signal-to-noise ratio indicated for the signal <NUM>. Raising the bit rate allows more data to be transmitted per period of time.

On a fading channel, the communication propagation path to the communicator's receiver <NUM> and the propagation path to the adversary's detector near the physical location <NUM> will typically fade independently. Therefore, if closed-loop power control were to be used to keep the transmitter at a power level that is minimally sufficient to close the communicator's link (as was done previous to the present invention), then when the communicator's link fades, the power of the transmitter <NUM> will be turned up to compensate. Since the adversary's link is likely not faded at the same time, this will make the communicator more detectable by the adversary <NUM>. Therefore, an appropriate countermeasure for this situation is to alter the rate rather than the power of the communicator's link. Then when the channel upfades, the rate of the link will go above average, and when the channel downfades, the rate of the link will drop below the average. As long as the feedback on the closed-loop rate control system is fast with respect to the channel coherence time, the loop will be able to keep up with the fading. The rate of the communication link on average will depend on the average channel path loss and the power transmitted by the transmitter <NUM>. Note that if the average rate is insufficient, the power can be increased at the expense of covertness, but once the power is set based on a long-term average of the channel conditions, including, for the example, the average magnitude of the noise floor, the data rate is allowed to fluctuate as the short-term fading dictates.

Referring now to <FIG>, a star topology network <NUM> is illustrated, including a hub receiver <NUM>, and a number of spoke transmitters <NUM>-<NUM> through <NUM>-n. Closed-loop rate control is a way to dynamically alter the rate of each communication uplink in a star topology network <NUM> in an attempt to properly balance the energy per bit received by a hub receiver <NUM>. This is important in CDMA systems, when covertness is considered important. When the energy per bit is perceived by the hub receiver <NUM> to be off from a target level, the data rate of that channel is adjusted through feedback to the spoke's transmitter (e.g., one of transmitters <NUM>-<NUM> through <NUM>-n), thus keeping the power transmitted by the spoke constant. A "Jam, Blank and Observe" detector therefore is rendered ineffective. Finally, information about the transmitters' priorities and knowledge of the applications carried over the links can be used to constrain the rate control algorithm to give preference to certain channel's rates over other channels.

Closed-loop rate control is also a countermeasure that can be used to keep a single link more covert on fading channels than is possible with closed-loop power control. Closed-loop rate and power control can be used together if desired to form a more comprehensive energy control function that operates with constraints not usually found in commercial systems.

Most CDMA systems use closed-loop power control to balance the energy per bit received of the uplinks from the spokes to the hub. Also on fading channels, even point-to-point links often use power control to keep the transmitted power as low as possible when covertness is considered to be important. Instead, embodiments illustrated herein can dynamically alter the data rate of the communication link rather than the power. This keeps the power radiated constant (or at least below some predetermined threshold) and in some cases less observable as a result.

Thus, closed-loop Rate Control can be used to accomplish one or more of keeping the power of the transmitted signal constant or below a predetermined threshold, thus making it harder for an adversary to detect. It can be used to implement more covert operation on a fading channel. Alternatively, or additionally, it can render a "Jam, Blank and Observe" detector ineffective.

In an alternative example, closed-loop rate control can be used, for example, for a military CDMA star topology network, in which it is desirable to keep the spoke's uplink transmissions to the hub as covert as possible. Imagine first a traditional CDMA system that uses closed-loop power control. If an adversary wanted to find the transmissions of the spokes (assuming they were too quiet to be seen from the location of the adversary initially), then the adversary could jam the hub's uplink frequency with energy, thus lowering the SNR of all of the uplink transmissions. The spokes would therefore be turned up by power control to higher power levels. If the adversary then suddenly blanked the jamming transmitter and sniffed the spectrum for the spokes' transmissions, the adversary would be able to see the transmitters more easily because they were turned up to higher levels. In this way, the "Jam, Blank and Observe" detector is able to bait the spokes to raise their power levels up (perhaps above the noise floor of the adversary's detector) and then by suddenly ceasing the jamming, the adversary can detect the uplink transmissions before the power control loop turns their signals back down to the original level.

In contrast, embodiments can implement a CDMA system that uses closed-loop rate control instead. This system sets the powers of the users (e.g., spoke transmitters <NUM>-<NUM> through <NUM>-n) at a minimally sufficient level to achieve the needed uplink rate under most circumstances. For example, the transmitters may be configured to transmit at a power level for a target SNR, assuming a known average (or minimum) noise floor. The hub receiver <NUM> alters the data rate of each uplink transmission, by indicating the SNR of signals received at the hub receiver <NUM> and/or directing data rate changes as appropriate, rather than the power transmitted when the uplink transmission energy per bit is deemed to be lower or higher than a target level. Now when a "Jam, Blank and Observe" detector is introduced by an adversary into the environment, the uplink jamming causes the data rates of the uplink channels to drop to lower levels, but the uplink powers remain unchanged. When the jammer ceases and observes the uplink spectrum, the adversary will not have succeeded in baiting any of the spokes into turning up their transmission power. The data rates would then rise back up under the control of the closed-loop rate control algorithm and the adversary would see no change in the noise floor.

Using aspects of this CDMA closed-loop rate control system, embodiments can be implemented which include quality of service and spoke priority. For example, if it is known by the hub that one user is sending a video uplink from a transmitter that requires, for example <NUM> kbps, and any rate below that will be insufficient, then the hub can use an all-or-nothing override on the rate control and lower other CDMA users using the transmitter that are employing more rate-flexible applications to favor the video uplink user, in an attempt to maintain this higher rate as long as possible.

In some embodiments, other users are notified to turn off completely, temporarily (by having their bit rate lowered to zero or near zero), in an attempt to provide enough signal-to-interference-plus-jamming-plus-noise ratio to keep the video channel alive. In other words, in some embodiments, closed-loop rate control mechanisms are application-aware, such that they can give rate preference to rate-sensitive applications at the expense of rate-insensitive applications. For example, referring now to <FIG>, some embodiments may include physical computer processors coupled to physical computer storage devices configured to store computer executable instructions which implement the closed-loop rate control mechanisms, such as the rate controller <NUM> illustrated in the transmitter <NUM>. Alternatively, or additionally, the rate controller <NUM> may be implemented using other mechanisms such as hardware programmable devices, logical gates, and/or other combinations of hardware, firmware, and/or software. Embodiments may include instructions or other flow control which allow applications <NUM> on a device such as the transmitter <NUM> to identify themselves and/or to identify a priority level of data being sent from the applications <NUM> to be transmitted using communication hardware <NUM>.

The communication hardware <NUM> is connected to the rate controller <NUM> which allows the rate controller <NUM> to provide data to the communication hardware <NUM> to be transmitted to various receivers as illustrated previously herein. The communication hardware may include for example various filters, amplifiers, modulators, antennas, transmission lines, and other appropriate components to propagate data on an appropriate medium for reception by one or more receivers.

The rate controller <NUM> receives data from the applications <NUM> and regulates the rate at which that data is provided to the communication hardware <NUM> for transmission on a transmission media, such as over the air. The rate controller <NUM> can prioritize data received at the rate controller <NUM> in various ways. For example, the rate controller <NUM> may include a comparison process that compares information from the applications <NUM> identifying the applications. In particular, an application may send application data to be transmitted by the communication hardware <NUM> along with an indication of the applications sending the data to be transmitted. The rate controller <NUM> can determine a priority level for the application and can determine what data rate the data from the application will be provided to the communication hardware <NUM> for transmission on the transmission media.

In an alternative or additional example, the applications can provide data with an indication of the priority level of the data itself rather than simply an indication of the applications sending the data. In this case, the rate controller <NUM> may include an algorithmically implemented comparator that is able to receive the priority information from an application, identify an appropriate data rate for the stated priority, identify available data rate bandwidth for communication on the communication hardware <NUM> to maintain an appropriate spectral flux density, and cause the data to be transmitted by the communication hardware <NUM> at a determined rate using the mechanisms described.

Embodiments may implement various contention resolution algorithms at the rate controller <NUM> when there is competition for bandwidth. For example, certain types of data may be known by the rate controller <NUM> to be mission-critical data, and will thus have priority over other data, even when the other data is also an indicated as being high-priority data and/or from a high priority application. Alternatively or additionally, the rate controller <NUM> may include a process that determines that the data is intended for a particularly important recipient and can thereby cause data for that recipient to have priority over other data for transmission on the communication hardware <NUM>.

Similarly, embodiments may be implemented where the CDMA closed-loop rate control algorithm is made aware of spoke priority levels, and can give rate preference to higher priority users at the expense of lower priority users.

It should be noted that embodiments setting the power levels of a set of transmitters that do rate control can also be implemented in some embodiments of the invention. Power levels are set in a way that keeps the transmissions as covert as possible, while maintaining a long-term average rate (averaged over fading, jamming, etc.) that is adequate to support the applications that the link needs to carry. In this sense, the CDMA closed-loop rate control algorithm can implement power control as well as rate control, and these two degrees of freedom can be managed together. For example, some embodiments may be configured to manage power based on the channel state over very long time periods, while managing rate over shorter time periods. Thus for example, in some embodiments power can be increased if it is determined that the noise floor has increased for a sufficiently long period of time as determined by comparison to some predetermined threshold, or other noise floor information. Alternatively, or additionally, power can be increased if it is known that additional noise raising the noise floor can be attributed to a source other than a jamming transmitter. For example, some embodiments may be able to determine an increase in the noise floor over a geographical area, and/or with characteristics that indicate that the noise floor is being raised due to some cause other than a jamming transmitter. For example, this could be due to cosmic radiation, weather conditions including lightning or other conditions, ignition systems, increased cellular traffic, solar flares, auroras, etc. embodiments may include the ability to gather information about one or more of these noise causing interference sources and to allow power to be increased when it is known that these noise sources are active. Indeed some embodiments may be able to determine a magnitude of noise attributable to an external noise source, and allow for an increase in power to increase the spectral flux density allowed corresponding to the increase in noise. Conversely, embodiments may be able to identify when noise sources are eliminated or reduced, and can therefore adjust the allowed spectral flux density accordingly. In these cases, it may be important to know the source of the noise to ensure that adjustments are not made for unknown noise that may be caused by adversarial jammers.

Note that embodiments illustrated herein may control spectral flux density to ensure one or more of low probability of interception (LPI), low probability of exploitation (LPE) or low probability of geolocation (LPG), etc..

Referring now to <FIG>, a method <NUM> is illustrated. The method <NUM> includes acts for transmitting a signal from a transmitter.

The method <NUM> includes identifying a threshold spectral flux density for a given physical location (act <NUM>). For example, as illustrated in <FIG>, the transmitter <NUM> may obtain information about what the spectral flux density of a signal should be at the physical location <NUM>.

The method <NUM> further includes, as a result of identifying the threshold spectral flux density, transmitting a signal at a power level causing the signal to be below the spectral flux density at the given physical location, the signal being transmitted at a data rate (act <NUM>). For example, as illustrated in <FIG>, the transmitter <NUM> transmits the signal <NUM> such that as it expands towards the physical location <NUM> the spectral flux density at the physical location <NUM> will be below a particular threshold for the spectral flux density. This threshold may be selected to ensure that the transmitter <NUM> remains undetectable, or at least has a low probability of detection, by the adversary <NUM>.

The method <NUM> further includes, receiving feedback from a receiver indicating the signal-to-noise ratio of the signal at the receiver (act <NUM>). For example, as illustrated in <FIG>, the receiver <NUM> provides a feedback message <NUM> to the transmitter <NUM> indicating the signal-to-noise ratio of the signal <NUM> received at the receiver <NUM>.

The method <NUM> further includes, adjusting the data rate of the signal based on the feedback (act <NUM>). For example, the transmitter <NUM> in <FIG> will adjust the data rate of the signal <NUM> to adjust the signal-to-noise ratio for the signal <NUM> received by the receiver <NUM>.

The method <NUM> further includes, continuing transmitting the signal at the adjusted data rate and power level (act <NUM>).

The method <NUM> may be practiced where the feedback is used to determine that signal-to-noise ratio should be increased, and wherein adjusting the data rate of the signal comprises lowering the data rate of the signal. In particular, more energy per bit will exist when the data rate is lowered and therefore increase the signal-to-noise ratio.

The method <NUM> may be practiced where the feedback is used to determine that signal-to-noise ratio should be decreased, and wherein adjusting the data rate of the signal comprises raising the data rate of the signal. For example, it may be determined that the data rate can be increased, and still maintain a particular desired signal-to-noise ratio, such that more data can be transmitted from the transmitter <NUM> to the receiver <NUM>.

Therefore, the data rate can be increased which will lower the signal-to-noise ratio, but not below a threshold signal-to-noise ratio required for communications between the transmitter <NUM> and receiver <NUM>.

The method <NUM> may further include determining that the transmitter has moved closer to the given physical location and as a result, lowering the power level, causing the signal to remain below the spectral flux density at the given physical location. For example, in some embodiments, a determination can be made for the location of the transmitter <NUM>, such as through the use of location hardware such as GPS, cellular triangulation, etc., and a determination can be made that the transmitter <NUM> has moved closer the physical location <NUM>. The power of the signal <NUM> would need to be reduced to maintain the desired spectral flux density at the physical location <NUM>. Thus, when it can be determined that the transmitter <NUM> has moved closer to the physical location <NUM>, then the power of the signal <NUM> can be reduced. Note that as used herein, the physical location <NUM> may actually be variable. That is, the adversary <NUM> may be mobile such that the physical location <NUM> associated with the adversary moves as the adversary moves. Thus, as used herein, determining that the transmitter has moved closer to the physical location may include determining that a static transmitter <NUM> is closer to the physical location <NUM> as a result of the physical location <NUM> changing. In alternative or additional embodiments, both the transmitter <NUM> and the adversary <NUM> may be mobile such that determinations may be made based on both the movements of the transmitter <NUM> and the adversary <NUM> to determine when power should be raised and/or lowered to maintain a particular spectral flux density at the physical location <NUM>.

In this context, the method <NUM> may further include determining that the transmitter has moved further away from the given physical location, and as a result, limiting an amount the power level is raised to cause the signal to remain below the spectral flux density at the given physical location.

The method <NUM> may further include identifying a quality of service requirement for the receiver. Some such embodiments may further include determining that the quality of service experienced by the receiver for the signal is above the quality of service requirement. Some such embodiments may further include, as a result, lowering the power level of the signal causing the quality of service experienced by the receiver for the signal to move toward the quality of service requirement while still causing the quality of service experienced by the receiver to be above the quality of service requirement. For example, it may be desirable to transmit with as little power as possible to ensure covertness of the transmitter <NUM>. However, there may be a quality of service requirement between the transmitter <NUM> and the receiver <NUM>. Determinations may be made that the quality of service can be maintained, even if the power of the signal <NUM> transmitted by the transmitter <NUM> is lowered. In these cases, the power can be lowered to a level that still maintains the required quality of service.

The method <NUM> may further include receiving feedback from a plurality of receivers where the feedback from each receiver in the plurality of receivers indicating the signal-to-noise ratio of the signal at that receiver. In some such embodiments, adjusting the data rate of the signal based on the feedback comprises adjusting the data rate to meet signal-to-noise ratio requirements for a receiver in the plurality of receivers experiencing the lowest signal-to-noise ratio, such that each of the receivers in the plurality of receivers receive the signal at a minimum required signal-to-noise ratio. Thus for example, there may be a number of different receivers in an environment where each of the different receivers provides a different feedback message indicating the signal-to-noise ratio for the signal <NUM> received at that particular receiver. In some embodiments, the data rate of the signal <NUM> may be adjusted based on the lowest signal-to-noise ratio reported from a receiver in the environment. Thus, while the signal <NUM> may be well above a certain signal-to-noise ratio for some receivers, it may be near or below a required signal-to-noise ratio for other receivers, resulting in the transmitter <NUM> reducing the data rate of the signal <NUM> for all receivers to ensure that the signal is able to be received by all receivers.

However, the method <NUM> may further include receiving feedback from a plurality of receivers where the feedback from each receiver in the plurality of receivers indicating the signal-to-noise ratio of the signal at that receiver. In some such embodiments, adjusting the data rate of the signal based on the feedback comprises adjusting the data rate to meet signal-to-noise ratio requirements for a receiver having higher priority than other lower priority receivers in the plurality of receivers such that the higher priority receiver receives the signal at a minimum required signal-to-noise ratio while one or more of the other lower priority receivers do not receive the signal at a minimum required signal-to-noise ratio. For example, it may be particularly important that certain receivers receive the signal <NUM> at a particular data rate such that it may be determined that other receivers will simply not be able to receive the signal <NUM>. In some embodiments, this can be done for a limited predetermined period of time. Alternatively, or additionally, this may be done cyclically. Thus, for example, in some embodiments the signal <NUM> may be transmitted at a certain data rate where all receivers can receive the signal <NUM> for a period of time, and then during a different period of time the signal <NUM> may be transmitted at a higher data rate, resulting in a signal-to-noise ratio acceptable only for some receivers in the environment that require receiving data at higher data rates, while other receivers are unable to receive the signal.

Embodiments within the scope of the present invention defined in the appended claims, also include physical and other computer-readable media for carrying or storing computer-executable instructions and/or data structures.

When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a computer, the computer properly views the connection as a transmission medium. Transmissions media can include a network and/or data links which can be used to carry desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer.

Claim 1:
A method of transmitting a direct sequence spread spectrum, DSSS, signal (<NUM>) from a transmitter (<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-<NUM>, <NUM>-n, <NUM>), the method comprising:
identifying a threshold spectral flux density for a given physical location (<NUM>) that is in proximity to an adversary (<NUM>);
as a result of identifying the threshold spectral flux density, transmitting the DSSS signal (<NUM>) at a power level causing the signal (<NUM>) to be below the spectral flux density at the given physical location (<NUM>), the DSSS signal (<NUM>) being transmitted at a data rate;
receiving feedback from a receiver (<NUM>, <NUM>) indicating the signal-to-noise ratio of the DSSS signal (<NUM>) at the receiver (<NUM>, <NUM>);
lowering the data rate of the DSSS signal (<NUM>) based on the feedback, wherein the feedback is used to determine that signal-to-noise ratio should be increased, or raising the data rate of the DSSS signal (<NUM>) based on the feedback, wherein the feedback is used to determine that the signal-to-noise ratio should be decreased; and
continuing transmitting the DSSS signal (<NUM>) at the raised or lowered data rate and power level.