Patent Application
20050159109
The present invention relates to wireless communications. More particularly, the present invention relates to techniques for detecting interference.
The unlicensed frequency bands of the electromagnetic spectrum are shared with a variety of systems. For example wireless local area networks (WLANs) and Bluetooth networks utilize the Industrial, Scientific, and Medical (ISM) band between 2400 MHz and 2483.5 MHz. In addition, microwave ovens, and harmonics of cellular telephony transmissions (such as GSM 850 and IS-95 transmissions) may cause interference in such unlicensed bands.
It is useful for short-range communications systems (e.g., Bluetooth and IEEE 802.11 networks) to recognize the traffic of neighboring systems. When constant regular transmissions by the interferers in the same channel are recognized, a network or device may avoid collisions with these regular transmissions by scheduling its own transmissions to be within other unoccupied channels or to be at times when other systems do not occupy the channel. Such avoidance reduces the number of retransmissions due to collisions, thereby enabling more efficient use of the band.
Bluetooth defines a short-range radio network, originally intended as a cable replacement. It can be used to create ad hoc networks of up to eight devices, where one device is referred to as a master device. The other devices are referred to as slave devices. The slave devices can communicate with the master device and with each other via the master device. Bluetooth devices are designed to find other Bluetooth devices within their communications range and to discover what services they offer.
Bluetooth networks may utilize 79 channels. Each of these channels has a 1 MHz bandwidth. To enhance robustness, Bluetooth networks perform frequency hopping among all or some of these 79 channels.
WLANs are local area networks that employ high-frequency radio waves rather than wires to exchange information between devices. IEEE 802.11 refers to a family of WLAN standards developed by the IEEE. In general, WLANs in the IEEE 802.11 family provide for 1 or 2 Mbps transmission in the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS) transmission techniques. Within the IEEE 802.11 family are the IEEE 802.11b and IEEE 802.11g standards, which are collectively referred to herein as IEEE 802.11b/g.
IEEE 802.11b (also referred to as 802.11 High Rate or Wi-Fi) is an extension to IEEE 802.11 and provides for data rates of up to 11 Mbps in the 2.4 GHz band. This provides for wireless functionality that is comparable to Ethernet. IEEE 802.11b employs only DSSS transmission techniques. IEEE 802.11g provides for data rates of up to 54 Mbps in the 2.4 GHz band. For transmitting data at rates above 20 Mbps, IEEE 802.11g employs Orthogonal Frequency Division Multiplexing (OFDM) transmission techniques. However, for transmitting information at rates below 20 Mbps, IEEE 802.11g employs DSSS transmission techniques. The DSSS transmission techniques of IEEE 802.11b/g involve signals that are contained within a 23 MHz wide channel. Several of these 23 MHz channels are within the ISM band. E
Current short-range communications systems provide techniques for measuring channel characteristics in a particular frequency band to find interfering systems or devices. However, these techniques are not ideal for collecting statistics of the interferences in the band.
For instance, IEEE 802.11b/g devices employ a carrier sensing technique before transmitting signals. This technique is known as Carrier Sensing Multiple Access/Collision Avoidance (CSMA/CA). CSMA/CA prevents collisions with other transmissions, which have already started. However, such techniques do not prevent collisions when two or more transmissions commence at the same time. Also, other systems that do not employ carrier sensing may commence transmissions while an IEEE 802.11b/g device is transmitting.
To avoid transmitting in channels employed by other systems, Bluetooth employs an adaptive frequency hopping (AFH) technique. With this technique, a frequency hopping Bluetooth device “hops around” channels that are used by other systems. However, before “hopping around” may begin, the devices in the Bluetooth piconet must first identify the static interferences.
Such identification involves measuring electromagnetic energy in the channels available to the Bluetooth piconet. When Bluetooth slave devices perform such measurements, they regularly transmit channel classifications to the master device, which decides which channels may be used for Bluetooth communications. The method to measure and classify the channels is not specified for Bluetooth. Channels can be classified based on received signal strength indication (RSSI) measurements in the slots when the piconet is not transmitting. In slots that the piconet is transmitting, channels are classified based on information regarding received packets, such as bit error or failed packet statistics. Bluetooth channels may also be classified based on a collaborative classification technique. Collaborative classification involves a host knowing other systems employed by the same device and classifies the channels utilized by the other system as “bad.”
A drawback of the above channel measurement techniques for detecting interfering transmissions is that they consume a considerable amount of “time, power, and bandwidth. This is because the measuring is time consuming, it is difficult to collect interference related information.
In addition, RSSI measurements require additional bandwidth and power consumption. For instance, background RSSI measurements can be made when there are not any transmissions in the network. In Bluetooth, it takes about 25 milliseconds (i.e., 79 times 312.5 microseconds) to measure all of the channels once during each 312.5 microsecond half slot. However, one measurement per channel does not reveal if the interference is static or hopping. Therefore, it takes about 250 milliseconds, if it is assumed that at least 10 measurements are required per channel to detect the static interference.
Because the network may not be able to stop its traffic for 250 milliseconds or even for 25 milliseconds, the actual time to measure the channels can be longer, depending on the utilization of the piconet. In addition, those 10 measurements have to be performed again after a short period to detect if some new static interference source has started transmitting, or if some old interference source has stopped transmitting.
In Bluetooth, the performance of error detection requires at least 100 ms (i.e., 79 times 625 microseconds times 2) to receive a packet in every channel, if the network utilization is 100% and only single-slot packets are used. Accordingly, the time for 10 measurements per channel is at least 1 second. However, if the utilization is not 100%, channel classification takes longer.
When the characteristics of the interfering transmissions are known, more efficient use of the band is possible. Accordingly, techniques are needed for the effective detection of interference sources.
The present invention is directed to a method, system, and computer program product that generates one or more electromagnetic energy measurements. Each of these measurements corresponds to an available communications bandwidth for a communications device. The method, system, and computer program product also identify one or more interference sources based on the measurement(s). Each of these measurements indicates a frequency of a radio frequency (RF) signal source. These measurements may include a series of electromagnetic energy measurements over a predetermined time period. An interference source may be identified when each measurement in the series of electromagnetic energy measurements indicates an RF energy source at the same frequency. Each of these measurements may be stored. In addition, statistics regarding these measurements may be generated.
The present invention is also directed to a wireless communications device having a communications module, an interference detection module, and a controller. The communications module exchanges information with one or more remote devices across a short-range wireless communications network. The interference detection module generates one or more electromagnetic energy measurements. Each of these measurements corresponds to an available communications bandwidth for the wireless communications device. The controller identifies one or more interference sources based on the measurement(s).
The present invention advantageously improves the detection of interference sources because interference sources are quickly detected over an entire frequency band that is available to a communications system. By generating several measurements of electromagnetic energy, the present invention may collect interference statistics and avoid transmitting at the same frequencies and times when other, interfering systems and device are transmitting. Furthermore, the present invention advantageously provides implementations that do not significantly increase device complexity.
Further features and advantages of the present invention will become apparent from the following description and accompanying drawings.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number. The present- invention will be described with reference to the accompanying drawings, wherein:
I. Operational Environment
Before describing the invention in detail, it is helpful to first describe an environment in which the present invention may be employed. Accordingly,
In particular,
In the environment of
In addition to non-communications related devices, devices associated with other communications systems may emit signals within the available communications bandwidth of short-range network 104. Examples of such devices include cellular base stations and phones. For instance,
Moreover transmissions from other short-range networks, such as neighboring short-range network 112, may be within the available communications bandwidth of short-range network 104. As shown in
These transmissions may interfere with transmissions in short-range network 104. Accordingly, devices and neighboring networks, such as the ones of
Interference sources may be static or dynamic. Static interference is more regular than dynamic interference. Accordingly, static interference is easier to detect. Bluetooth interference is fairly unpredictable, because it hops randomly over the ISM band. However, interference from IEEE 802.11b/g networks is more predictable (and thus more static) because transmissions from these networks are direct-sequence spread spectrum systems that are contained within a channel that is 23 MHz wide. Interference from microwave ovens is also fairly static because of their fairly constant spectral content.
The present invention provides techniques for identifying interference sources. Once identified, one or more devices in a wireless network, such as short-range wireless network 104, may transmit signals in a manner that avoids interference from these identified sources.
II. Wireless Communications Device
Receiver front end 210 includes a receive antenna 212. In addition, receiver front end 210 may include additional components, such as a low noise amplifier (LNA) 214, and a bandpass filter 216 tuned to an available communications bandwidth. Through receiver front end 210, the device receives transmissions associated with its short-range network, as well as energy (i.e., signals) from interference sources. From these transmissions and signals, receiver front end 210 generates an RF signal 220, which is sent to both interference detection module 202 and communications module 204.
Interference detection module 202 produces energy detection indicators 222 (also referred to herein as measurements), which indicate the presence of energy at certain frequencies in RF signal 220. These indicators are sent to controller 206. Interference detection module 202 is described in greater detail below, for example, with reference to
Communications module 204 handles the exchange of information across a wireless network, such as a Bluetooth or an IEEE 802.11b/g network. Accordingly, communications module 204 may govern processes, such as device discovery, paging, connection establishment, authentication, and encryption. For instance, in the context of Bluetooth communications, communications module 204 may include a Bluetooth module. In addition, communications module 204 may exchange information with higher level processes. (e.g., applications).
As described above, communications module 204 exchanges signals with remote devices via a wireless communications network. This involves receiving signals through receiver front end 210 and transmitting signals through power amplifier 221, which is coupled to transmit antenna 218. Accordingly, communications module 204 may include components, such as modulators and demodulators to handle the reception and generation of such signals.
Controller 206 receives energy detection indicators 222 from energy detection module 202. These indicators may be stored in memory 208 as part of an operation to collect energy measurement statistics. In addition, controller 206 receives resource allocation information from communications module 204. This information identifies portions of the available communications bandwidth (e.g., channels, frequency ranges, and/or time slots) used by the wireless communications network(s) in which the device is participating.
Based on received energy detection indicators 222, controller 206 identifies interference sources, such as static interference sources. This identification may also be based on resource allocation information from communications module 204 so that any energy detection indicators 222 associated with legitimate signals are disregarded. From this identification, controller 206 directs operation of communications module 204. For example, controller 206 may indicate to communications module 204 portions of the available communications bandwidth (e.g., channels, frequency ranges, and/or time slots) that are subject to interference. Based on such indications, communications module 204 may avoid transmissions in such portions of the available communications bandwidth.
The elements of
Controller 206 may be implemented in various ways. For example, controller 206 may be implemented with one or more microprocessors (e.g., as a computer system) executing software instructions stored, for example, in memory 208. Alternatively, controller 206 may be implemented in firmware and/or hardware, such as application specific integrated circuits (ASICs).
Similarly, communications module 204 and interference detection module 202 may be implemented with one or more microprocessors executing software instructions stored, for example, in memory 208. However, these components may additionally be implemented with electronics and/or DSP(s).
Memory 208 may include, for example, random access memory (RAM), read only memory (ROM), and/or flash memory. Communications module 204 may be implemented through one or more devices, such as microprocessors, electronics, and digital signal processors.
Although,
Oscillator 302 is tuned to a predetermined frequency, such as the center frequency in an available communications bandwidth. For instance, when the available communications bandwidth is the ISM band, oscillator 302 may be tuned to 2441.75 MHz. As shown in
Oscillator signal 320 is also sent to phase shifter 304, which introduces a 90 degrees phase shift. This phase shift yields a quadrature oscillator signal 322, which is sent to mixer 314b of quadrature path 308. Oscillator signals 320 and 322 may be substantially sinusoidal.
Mixers 314a and 314b are each coupled to front end 210. Accordingly, each of mixers 314a and 314b receives RF signal 220 based on emissions collected by receive antenna 212. RF signal 220 is downconverted by mixers 314a and 314b. The amount of this downconversion depends on the frequency of oscillator signals 320 and 322. Accordingly, mixer 314a generates a downconverted in-phase signal 326, while mixer 314b generates a downconverted quadrature signal 327.
Low-pass filters 316a and 316b each have bandwidths large enough to accommodate the available communications bandwidth. For instance, these filters may have a 3-dB bandwidth of 40 MHz. As shown in
Comparison module 310 may be implemented in various ways. For instance, comparison module 310 may include a differentiation node, which subtracts one of signals 328 and 330 from the other. Such operations produce a clock signal 332 having a frequency associated with the strongest energy source (e.g., the strongest interference source) in RF signal 220. Clock signal 332 is sent to spectral identification module 312.
Spectral identification module 312 determines the frequency associates with clock signal 332. This module may be implemented in various ways. As an example,
As shown in
Based on the length of such intervals, a frequency value may be calculated. Such a calculation may be made, for example, by dividing the counter value by the interval duration and adding an offset based on the frequency of the oscillator 302. This determined frequency value corresponds to the strongest energy source in the frequency range monitored by implementation 300. In embodiments, such calculations are performed by controller 206.
This monitored frequency range is determined by the frequency of oscillator 302 and the bandwidth of low-pass filters 316a and 316b. Thus, implementation 300 may be used to monitor an entire communications bandwidth at once. However, implementations of interference detection module 202 may be used in which a portion of an available communications bandwidth is monitored. An example of such an implementation is provided in
The implementation of
Oscillator 404 is tuned so that it corresponds to a particular sub-band (e.g., a 10 MHz wide sub-band) within the available bandwidth. For instance, oscillator 404 may be tuned to the center frequency of the particular sub-band. Low-pass filters 406a and 406b each have bandwidths large enough to accommodate a sub-band. For instance, these filters may have a 3-dB bandwidth of 5 MHz.
In
f=fch1+nfch
In the above equation, fch1 is baseline frequency value beneath the lowest sub-band in the available communications bandwidth, and n is the index of the particular sub-band to which interference detection module 202 is tuned.
The implementations of
Simpler implementations of interference detection module 202 are shown in
Unlike the implementations of
Downconverted signal 522 is sent to spectral identification module 312′. As shown in
With implementation 500, the polarity/sideband sign of RF signal 220 is lost. However, bandpass filter 216 of receiver front end 210 may be configured to provide sufficient attenuation in order to quite reliably determine which channels are blocked by interference sources.
The implementations of interference detection modules 202 shown in
III. Interference Detection
As described above, controller 206 may determine time intervals in which counters 317 output their values as energy detection indicators 222. In embodiments, controller 206 may establish intervals in which each counter 317 outputs a series of associated indicators 222. Such a series may occur for example, at regular intervals during a particular time period. This results in a measurement corresponding to the time period that is based on the series of indicators 222 (also referred to herein as sub-measurements). In one such example, each counter 317 outputs indicators 222 at 10 microsecond intervals during a 100 microsecond period. This results in a measurement associated with the 100 microsecond period.
Such techniques may be used to identify interference sources. For instance, the presence of an interference source is probable when, during a measurement for a particular frequency range, each sub-measurement indicates the strongest RF energy source at the same frequency. When this occurs, embodiments of the present invention may determine whether the energy from this source is strong enough to interfere with the traffic in the network(s) in which the device is participating. Such determinations may involve making an RSSI measurement of this received energy.
In contrast, the presence of noise is probable when, during a measurement for a particular frequency range, each sub-measurement indicates the strongest interference at different frequencies.
In embodiments of the present invention, such measurements may be performed at regular periods. Further, the results of each measurement (e.g., each sub-measurement) may be stored in memory 208. In one exemplary implementation, a certain number of previous measurements (e.g., the last 100 measurements) are stored in memory 208. This storage may include each individual sub-measurement. This allows controller 206 to analyze patterns and/or regularities of energy from interference sources. Such analysis may involve the generation of statistics from these measurements. From this, the possible regularity of an interference source may be identified. In devices and communications networks that are unable to change to other frequencies, this feature advantageously enables the scheduling of transmissions in the time domain to avoid interference from such sources.
This sequence begins with a step 702 in which one or more electromagnetic energy measurements are generated. Each of these measurements corresponds to an available communications bandwidth for a communications device. For instance, with reference to the environment of
Alternatively, the available communications bandwidth may be divided into multiple portions, such as 10 MHz sub-bands. Accordingly, in such embodiments, each of these measurements of step 702 corresponds to a particular selected portion (e.g., sub-band) of the available communications bandwidth. This division of the available bandwidth into portions and selection of portions may be performed by controller 206.
Each of the measurement(s) in step 702 indicates a frequency of a radio frequency (RF) signal source. Examples of such signal sources include the external devices described above with reference to
In the device implementation of
In a step 704, one or more frequencies that correspond to one or more interference sources may be identified based on the measurement(s) generated in step 702. When step 702 includes generating a series of measurements (i.e., sub-measurements) over a predetermined time period, step 704 may include identifying an interference source when each sub-measurement indicates an RF energy source at the same frequency.
In a step 705, the device determines whether any of the interference source(s) are strong enough to hinder communications for any networks in which the device is participating. For example, this step may include generating one or more RSSI measurements. If the interference is sufficiently strong to hinder communications, then the device may initiate actions so that network resource allocation avoids such interference sources. For example, the device may avoid transmitting signals in certain frequency channels.
In a step 706, the communications device stores the measurement(s) from step 702. With reference to the implementation of
In a step 708, the communications device may generate and/or compile statistics based on the measurements stored in step 706. Such statistics may be used to identify transmission patterns (likely times of interference) at various frequencies of the available communications bandwidth.
The steps of
The techniques of the present invention advantageously provide for the measurement of an entire communications bandwidth in a short amount of time. For example, a whole communications bandwidth can be measured once in about 1 millisecond. As described above, this measurement may includes a plurality (e.g., 10) sub-measurements. Accordingly, the present invention provides a significant reduction in time, power, and bandwidth consumption.
Furthermore, the present invention allows for a more effective collection of interference statistics pertaining to the whole communications bandwidth. This is because, with conventional techniques, interfering systems (such as static interferers) may have stopped transmitting signals before the possible regularity of their transmissions have been detected.
IV. Conclusion
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not in limitation. For instance, although examples have been described involving Bluetooth and IEEE 802.11 technologies, other short-range and longer range communications technologies are within the scope of the present invention.
Accordingly, it will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.
