Program for scanning radio frequency channels

The Easier to Read manuals for the various RS scanners are linked below. In addition we have a number of programming shortcuts for older RS radios, as well as user's guides for some of the more popular programming packages. Please see our Connecting scanners via USB article for more information and tips on how to set this up properly.

The RadioReference Wiki. How do I program my insert model number scanner? The method of programming is confusing. To make your listening experience smooth and static-free, make sure you also got a proper antenna installed in your scanner. This is not illegal.

You can hack frequencies using devices other than scanners. Imagine listening to a police radio frequency in your area about local crime on your scanner. Fortunately, you can use other devices to hack into the spectrum beyond FM. What you have is a radio that you built yourself. An additional perk is it might double as something else too, like a simple calculator.

This will enable you to listen to coded audio data. You can then decode these audio signals and effectively make out what the police are saying about crime in your local area. Welcome to RatedRadarDetector. RRD is reader-supported.

When you purchase through links on our site, we may earn a commission. Read more. Table of Contents How to find police scanner frequencies? What frequencies do scanners use? How do you program police frequencies? Can you get in trouble listening to police frequencies? How can you listen to police frequencies? The distance to the farthest associated STA 16 is compared to the distance to the closest AP 12 operating on the same channel step If the distance to the farthest associated STA is greater than the distance to the closest AP operating on the same channel step , then the Max TP backoff value is adjusted back down to accommodate this STA step , and the AP's TP backoff is set to this adjusted value step Power adjustement may be repeated every second, for example, in an In accordance with the preferred embodiment for use in a wireless data networking environment, as shown in FIGS.

In many wireless networking architectures, it is possible for several APs to occupy the same channel while serving different physical networks. For example, in the When set to false, the AP 12 will ignore any other APs on the same channel who's physical network is different from this AP 12 's physical network e. This option is useful for cases when there are multiple APs in relatively close proximity that are on different networks.

In this case, the operator may prefer to run his AP at the maximum power level to provide the best possible signal for all stations on his network.

The Hello Interval is architecturally and design dependent. The knownAPs table entries are first aged before other processing is performed. The age of each entry is incremented step , and any entries whose age exceeds Max AP Entry Age are deleted steps , Thus, if an AP hasn't been heard from in a while, it is aged out of the table to prevent it from affecting this AP 12 's power adjustment calculations.

The greater the number of samples used to derive the value, the more accurate the measurement. The AP accounts for the inaccuracy in this value by subtracting a standard error, based on the sample size, from the normalized power level, as shown in the following formula.

Note, in an For example, table I in FIG. The AP's noise floor is a measure of background power on the channel. It therefore leaves its Max TP Backoff value at 0 step Claim, Announce, Accept at full power. So, APs can always hear management messages passed between each other. Furthermore, various different wireless networking architectures may provide a mechanism for clearing the wireless channel, further increasing the probability that the management messages will be received.

After sending the Announce message at maximum power level, the AP resumes use of its calculated TP backoff value for data packets to minimize same-channel interference, as described above. The Banzai is a unit of distance derived from a measurement of received signal strength from an AP 12 operating with a known transmit power backoff. A transmit power backoff is generally expected to range in value from 0 dB to 65 dB. Algorithms for movement detection are described in more detail later.

The AP 12 detects movement by continuously checking to see if the difference between the distance to each station, derived from a set of long term samples, is sufficiently smaller that the current distance measurement based on the most recently collected samples, to indicate that the STA 16 is moving away from its AP The difference between the long term distance and short term distance values is compared to a Moving Threshold value plus the standard error in the two distance measurements in order to eliminate false movement detection.

See section 6 for more information. A station is considered to be moving when the short term distance exceeds the long term distance by more than the Moving Threshold plus the sum of the errors in the two measurements.

The following pseudo code describes this comparison. If the AP 12 determines that it is no longer moving before the STA 16 loses the association to its AP, the AP 12 resumes normal processing of received signal strength to determine a new appropriate TP Backoff value as previously described step The AP 12 looks to see when this difference is less than just the standard error in the two measurements to determine that the STA 16 has stopped moving.

This test is performed as follows step :. The purpose of the Auction is to accomplish the distribution of STAs 16 across APs 12 in a manner that optimizes wireless communications performance.

This value is called the biased distance delta. In particular, referring to FIG. If a Bid is received from a STA 16 from which a Bid has already been received step , the new bid information replaces the previous bid information step Otherwise a new entry is created for the STA 16 step In either case the bid entry's age is reset step At the end of Auction Interval step , the AP 12 processes the received bid information. The Auction Interval in an exemplary The age of all bid entries is incremented by one step and then any bid entry whose age is greater than Max Bid Age is deleted step The IDs of each STA 16 being sent an Accept is put in a list of outstanding accepts step , and a count of accepted STAs who have not yet associated and registered is noted as numAcceptsOut step At this point the next auction period begins.

Any bid information found for the newly associated STA 16 is deleted step The AP 12 also checks to see if the STA 16 is in the list of outstanding accepts step , and if the STA 16 is in the accepts outstanding list that entry is deleted step and the numAcceptsOut count is decremented step At the end of the Auction Interval, any outstanding accepts from the previous auction cycle are considered to have timed out, hence the list of outstanding accepts is emptied and numAcceptsOut is reset.

These processes continue as long as the AP 12 is active on a given channel. First, the STA 16 scans for beacons on all channels across all supported bands e. Preferably, where multiple bands are supported, the selection of an AP 12 also takes into account a preference for the higher bandwidth bands so that, for example as implemented in an Any security policies that control association are executed at this point.

Once it has made its initial association and has access to the wireless LAN, the STA continuously performs the following functions to optimize its configuration:. In order to monitor DRCP Announce messages, a STA 16 periodically tunes its radio to the channels other than the one to which it is currently associated. However, the STA 16 must remain associated to its current AP 12 so that it does not lose data packets. So, packets must be buffered during the time that the STA 16 is canvassing.

Various wireless communications architectures may provide different means for packet buffering. Generally, referring to FIG. Packet buffering can be initiated in a variety of ways. This information is used by the AP 12 to determine whether to bid for another AP. When the scan interval is complete, packet buffering is turned off and the STA 16 receives its buffered packets from the AP 12 step The STAs 16 can indicate to APs 12 that they are entering this power save mode.

STAs 16 wake up in response to these special Beacon messages. These Beacon messages include information as to whether any data is buffered for the STA STAs 16 operating in an After the channel canvass is complete, the STA 16 reverts to normal power save mode.

STAs 16 that have already been set to Power Save Mode by management will have even more time to canvass. The power save mode that was set by management active, power save is remembered step The power save mode is set to power save, and the listen time time the STA 16 stays asleep , if any, is increased by a period of time herein referred to as scan time step At the beginning of the power save cycle, the STA 16 actually stays awake temporarily, instead of dozing as it told the AP it was going to do.

It is during this time that other channels are canvassed for beacons and DRCP Announce messages step After the canvass is done the STA 16 resumes its power save cycle step This process repeats every scan interval.

Whenever the STA 16 is not canvassing, it restores the remembered management set power save mode. The scan interval may be for example twice per Beacon interval. Stations that have not been set to Power Save Mode by management are caused by the STA 16 to act as if they've been set to Power Save Mode, with listen interval set to the minimum value i.

STAs 16 that have already been set to Power Save Mode by management will have the most amount of time to canvass. The STA 16 keeps track of which channels have been canvassed, stepping through all of the channels until all supported channels have been canvassed.

If found, the STA updates the entry step , otherwise it creates a new one step , up to a previously set maximum herein referred to as Max APs entries step The STA 16 also notes the received power level that accompanied the beacons and Announce messages and uses these values along with the TP backoff values to calculate the distance to the APs in Banzais, as previously described.

The received power level value and correspondingly, the distance in Banzais, are subject to variability in the RF channel. The STA 16 saves a number of these distance measurements for each entry in the knownAPs table, so that it can use averaging to compensate for this variance, to be further described.

For its own AP i. Additionally, the STA keeps an Age for each entry. Entries are aged as part of the STA Bidding process, described below. When the canvass is complete and a sufficient number of samples have been collected on each channel step , the STA knownAPs table entries are aged before other processing is performed step The age of each entry is incremented, and any entries whose age exceeds Max AP Entry Age are deleted step As mentioned, the STA 16 uses averaging to compensate for variance in its distance measurements.

This is to avoid making a decision to move to a new AP before it has sufficient information about the other APs in the network. However, to avoid the potential for waiting indefinitely, it will not delay processing the knownAPs list for any new APs that were added after it has Long Term Sample Size distance values for its own AP. Working with the entries for which there are sufficient distance measurement samples, the STA 16 looks for a potential better AP.

In summary, a biased distance is calculated for each entry, which takes into account the available data rate as well as the loads on the APs step The data rate is deduced based on the received signal strength and the technology being used i.

After calculating the biased distances for all of the entries in the STA knownAP table, the AP with the lowest biased distance is considered to be the best candidate and, if it appears better than its current AP step , a Bid is sent step As previously noted, this value is subject to variance in the RF channel. It is advantageous to minimize the error in the distance measurement for a given entry n, in comparison to the STA's current AP.

This is done by using a corrected distance that is set to the distance to the STA's current AP, if the entry falls within the sum of the standard errors on the two distance measurements. This distance is then used in conjunction with data related to the particular wireless environment in which the AP 12 is operating to derive an estimate on the expected load factor for the STA. For example, in an One skilled in the art will realize how to implement distance-to-rate and rate-to-load tables from specifications for other wireless environments.

That is:. This helps to support a consistent view of the load of that AP both before and after a STA associates with it—that is, since the STA adds its own load to the default load of its prospective non-DRCP AP before it makes a decision to associate with it, it must also add its load to the default load for this AP after it has associated with it.

The biased distance is calculated as described by the following formula:. This calculation is made as follows:. To detect movement, the STA 16 compares the distance to its AP 12 , derived from averaging over the long term using Long Term Sample Size, to the short term distance, derived from averaging the most recent Short Term Sample Size samples.

This difference is compared to a Moving Threshold value plus the standard error in these two measurements in order to eliminate false movement detection. Once the STA 16 detects that it is moving step , and as long as the STA 16 does not detect that it has stopped moving, the STA 16 refrains from participating in the bidding process step , seeking a new AP only if warranted by the deterioration of its current association.

The STA 16 looks to see when this difference is less than just the standard error in the two measurements to determine that the STA 16 has stopped moving. The following pseudo code describes this test. Software Architecture. In accordance with the preferred embodiment, the previously described functionality is implemented in software in APs 12 and STAs 16 respectively. This architecture is advantageous for porting the inventive functionality between different wireless architecture platforms.

In environments where the APs 12 are connected to each other via a wired network 14 , DRCP messages may be passed directly between the APs 12 via the wired network The ARM software is actually implemented within several different More information on these elements can be found in the incorporated As shown, the SRM communicates with various Likewise, the AP radio manager is the platform dependent portion of the AP software, communicating with These DRCP messages are now described in further detail.

But, according to the preferred embodiment as implemented in an The fixed portion of the Beacon frame is as defined in the In accordance with a preferred embodiment, it is desirable for DRCP enabled APs to perform automatic channel selection and load balancing by exchanging DRCP Claim, Preclaim, and Announce messages in management frames of subtype Beacon, while preventing STAs from attempting to associate with an AP in response to receipt of one of these messages.

Several steps are therefore taken in addition to the DRCP protocol specific address fields already mentioned. Furthermore, standard non-DRCP Refer to the incorporated Management frames of type Beacon encoding It is noted that the DRCP protocol could be implemented over non primitives without departing from the principles of the invention.

The following describes the primitives used in an In particular, the semantics of the The received power parameter specifies the signal strength, expressed in dBm, at which the MSDU was received. The received power value indicates the current level at which the sending device is heard, but does not provide an indication of whether or not the sending device is transmitting at full power.

The potential power level at which a device-might be heard can be determined when the transmit power backoff i. An additional element is added to this list:. Send DRCP. Message Unsigned CTS unsigned The value represents the time, in microseconds, required to transmit the pending Beacon frame, plus one short interframe space SIFS interval. This parameter is only used when the quiet channel parameter is true. The primitive parameters are as follows:.

This mechanism supports a STA's ability to indicate to the AP that it is in power save mode, without actually going into power save mode. This primitive requests the SME to use the power save mode interaction with the AP to allow time to canvass other channels.

This primitive confirms the change in power management mode to the SRMA. The SRMA is thus notified of the change of power mode indicated. This mechanism notifies the SRMA that it can begin to canvass. This primitive indicates to the SRMA the start of the power save cycle. This primitive is generated by an SME to indicate the start of power save cycle.

The SRMA is thereby notified of the start of the power save cycle. This mechanism further supports a STA's ability to indicate to the AP that it is in power save mode, without actually going into power save mode. This primitive tells the MLME that it should restore the user-configured power save mode.

This primitive is generated when the canvass mechanism is taken out of service. The receipt of this primitive causes the SRM to restore the saved power management mode settings and:. It is not generated until the change has been indicated.

Upon receipt of this primitive, the SRMA is notified of the change of power mode indicated. This primitive tells the MLME that it's safe to enter the awake state and transmit frames if desired. This primitive is generated when the SRMA is has completed canvassing. Upon receipt, the MLME enables transmission of user data frames, if necessary. This primitive confirms the change in allowed power management state. Receipt by the SRMA serves as notification of the change of the allowed power save mode.

This mechanism supports the ability to indicate to an ARMA that a channel has gone out of service. This primitive reports to the ARMA that a channel that was previously available has become unavailable.

This primitive is generated by the MLME when a channel becomes unavailable. Receipt of this primitive causes the ARMA to remove the channel from its channel map. This mechanism provides the ability to indicate to an ARMA that a channel has gone into service. This primitive reports to the ARMA that a channel that was previously unavailable has become available.

Receipt of this primitive causes the ARMA to add the channel to its channel map. Beacon Notify This mechanism supports the ability to detect any other APs using the same channel. There is one indication for each Beacon received. An indication is generated any time a Beacon is received on the current channel.

When False, this mechanism is to be disabled. This primitive is generated by an ARMA when it wants to be notified of any beacons received on its own channel.

This primitive confirms the change in the beacon notification mechanism. This primitive is generated by the MLME if a beacon is received on the data channel. The following describes the manner in which the above described primitives are used to implement DRCP messages in an As previously described, APs and STAs ascertain movement based upon evaluation of short and long term averages of parameters, along with expected error measurements.

In accordance with an aspect of the invention, movement detection is achieved through application of a broader inventive concept that provides a way to ascertain the dynamic attributes of a system based upon short and long term averages of discrete data measurements.

The principles of this invention apply to any system in which a discretely measured variable may change widely. For purposes of clarity, however, the invention is now described in terms of its particular application to wireless networks.

In a wireless network such as the one shown in FIG. The AP provides associated users with network connectivity via radio frequency RF signals. Various APs are used to provide seamless RF coverage, so that when the user moves away from one AP toward another AP, the user will associate with the closer AP or the AP that is more lightly loaded and seamless network functionality is thereby maintained.

It is therefore important to be able to ascertain the location of a user relative to an AP so that a determination can be made as to whether the user is currently moving. This allows the system to assure that the user rapidly becomes associated with the closest AP so the overall system performance is maximized. As a user moves toward or away from an AP, the received power level i.

Thus, one way to ascertain user movement is by monitoring received power levels. However, received power levels can appear to vary greatly even when a user is not moving. For example, the opening or closing of a doorway can cause either a gain or attenuation in the user's received power level. A person waving their hand near the user's antenna can even cause a gain or attenuation in received power level.

Environmental interference can also cause changes in received power levels. These various changes in power level can cause a user to appear to be moving when in fact he or she is not. This can cause the user to roam needlessly between APs, particularly in environments where APs are close together and their transmit power levels are lower than maximum power.

Alternatively, variations in signal power due to these effects can mask the fact that the user is indeed moving. In this case, the system could fail to detect the motion and fail to associate the user with the appropriate AP.

As can be seen, the inaccuracies in data sampling prevent any assumption of movement in one direction or the other.

As a more particular example, consider an APs in such a network provide a maximum bandwidth of 54 Mbps. Bandwidth drops with distance from the AP. Assume that adjacent APs have their transmit power adjusted so that each provides a 54 Mbps cell on the order of about 10 feet in diameter.

A walking user might be able to transition through such a cell in 2 seconds. On the other hand, a user sitting at his desk near the center of the cell, right next to the AP who gets up and leaves travels only 5 ft, not 10 ft to the edge of the cell—so, it may take the user only just over a second to be in the aisle and out of the cell.

These examples provide a motivation for why rapid power estimates based on discrete measurements must be made. Increasing sampling rates increases accuracy, but this also causes more overhead in terms of wireless channel bandwidth, interrupt activity and processing overhead on the user device. Some user devices could be simple appliances such as phones, digital assistants, etc. So a trade-off must be made between sample rate and overhead.

According to one possible implementation, power levels are measured at intervals over a window of time and a roaming decision is made. Yet, there is a variability to the measurements because of environmental effects hand waving, etc. A false positive occurs when a user is ascertained to be moving when in fact he or she is not, causing the user to needlessly roam to another AP.

It is desirable to minimize such false positives as they needlessly consume valuable bandwidth. When a user doubles his or her distance from an AP, the user's received power decreases by 6 db.

But, as seen in FIG. This is because the true mean is really unknown. So, when only these few samples are taken, it cannot be ascertained whether the user is moving away from the AP, getting closer to the AP, or not moving at all. Of course increasing the number of samples taken decreases the range of error. But, taking lots and lots of samples will take too long unless channel overhead is increased. Now consider taking n samples to produce an estimate, and then taking n more to produce a second estimate.

The two estimates are then compared to see if a conclusion can be drawn as to whether the user is moving. If the confidence intervals around each estimator are large, e.

In FIG. Consider two basic scenarios regarding motion in wireless networks:. In the instance of scenario 1 , which describes the very large majority of user activity in wireless networks, the accuracy of the power estimate can be greatly improved. In accordance with the principles of the invention, two averages of the received signal strength are maintained as above.

But, one is the most recent N 1 samples taken over a sliding window, and the other is a long term average, using N 2 samples. So both a long term average and a short term average are maintained. The error in the estimate is almost completely removed. Therefore, the potential uncertain outcomes in the decision are reduced. For a given application, one needs to ascertain how many samples N 2 must be taken such that the long term average estimate has essentially 0 error.

Assume a user starts at a position 1 foot away from the AP and moves towards the edge of the 10 ft cell. In this wireless network example, it has been assumed that a user can walk from the center of the cell to the edge of the cell in 1. So, samples need be taken every 1. As a further improvement, it would be desirable to use 16 samples so that division can be done by a processor via a shift operation.

This increases computational efficiency on the user's machine. This increases the sample rate a negligible amount. The tighter this interval needs to be, the longer the user has to stay near the AP, or stay relatively stationary within a certain area, to cause the average to converge.

Assume, reasonably, that signal strength samples are taken based on messages received from the AP every 50 milliseconds. Referring to the table shown in FIG. The process is as follows:. In an environment where users tend to remain in a cell for less than 1 second, the long term estimate could be used based on fewer samples.

However, this will result in an increased risk of false positives. Several alternatives can be considered to mitigate the occurrence of false positives:. To generalize, in a system wherein particular dynamic attributes are to be ascertained e. An acceptable difference between the short and long term averages is calculated which positively identifies the system characteristic e. The user sends messages to the AP that indicate the received signal strength from the AP as perceived by the user.

These messages are collected by the AP