WO2003081925A1 - Selection de canal dynamique dans des modems sans fil - Google Patents

Selection de canal dynamique dans des modems sans fil Download PDF

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Publication number
WO2003081925A1
WO2003081925A1 PCT/US2003/007450 US0307450W WO03081925A1 WO 2003081925 A1 WO2003081925 A1 WO 2003081925A1 US 0307450 W US0307450 W US 0307450W WO 03081925 A1 WO03081925 A1 WO 03081925A1
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WIPO (PCT)
Prior art keywords
channel
available
metric
available channels
channel metric
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Application number
PCT/US2003/007450
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English (en)
Inventor
Javad Razavilar
Poojary Neeraj
Dennis P. Connors
James A. Crawford
Original Assignee
M2 Networks, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US10/101,891 external-priority patent/US20030181211A1/en
Application filed by M2 Networks, Inc. filed Critical M2 Networks, Inc.
Priority to AU2003218091A priority Critical patent/AU2003218091A1/en
Publication of WO2003081925A1 publication Critical patent/WO2003081925A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
    • H04W16/02—Resource partitioning among network components, e.g. reuse partitioning
    • H04W16/10—Dynamic resource partitioning
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W24/00—Supervisory, monitoring or testing arrangements
    • H04W24/10—Scheduling measurement reports ; Arrangements for measurement reports
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/02—Selection of wireless resources by user or terminal
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/54—Allocation or scheduling criteria for wireless resources based on quality criteria
    • H04W72/541—Allocation or scheduling criteria for wireless resources based on quality criteria using the level of interference

Definitions

  • the present invention relates generally to the selection of channels for communication in a communication system, and more specifically to the selection of channels based on measurements of received signal strength on a number of available channels.
  • communicating terminals may select one of several available channels in the operating band over which to communicate.
  • Co-channel interference and adjacent channel interference are components of interference that degrade performance in a wireless link.
  • Systems have been devised to select, for communications, one of the multiple available channels that has a relatively low overall interference level in comparison to other available channels.
  • received signal strength measurements are taken at an antenna of a receiver in order to produce a histogram of the received signal strength for each available channel.
  • the histogram (which is based on the magnitude of the interference level) is then used to select a desired available channel.
  • MAC synchronous media access control
  • the present invention advantageously addresses the needs above as well as other needs by providing a dynamic channel selection algorithm in a communication system for selecting an available channel for use out of multiple available channels.
  • the invention can be characterized as a method, and means for accomplishing the method, of selecting between available channels, the method including the steps of: determining a channel metric corresponding to measurements taken at a receiver for each of a plurality of available channels, the channel metric indicative of a level of interference in each of the plurality of available channels; sorting the plurality of available channels according to their respective channel metric; determining whether co-channel signaling is present on an available channel having a lowest channel metric of the plurality of available channels; and selecting one of the plurality of available channels based upon at least the determining whether the co-channel signaling is present on the available channel having the lowest channel metric.
  • the invention can be characterized as a channel selection device for a communication terminal of a communication system comprising a dynamic selection module configured to perform the following steps: determining a channel metric corresponding to measurements taken at a receiver for each of a plurality of available channels, the channel metric indicative of a level of interference in each of the plurality of available channels; sorting the plurality of available channels according to their respective channel metric; obtaining an indication whether co-channel signaling is present on an available channel having a lowest channel metric of the plurality of available channels; and selecting one of the plurality of available channels based upon at least the determining whether the co- channel signaling is present on the available channel having the lowest channel metric.
  • the invention may be characterized as a method for selecting between available channels, the method including the steps of: receiving a plurality of received signal strength measurements corresponding to L discrete received signal strength measurements taken at an antenna within a time period of a measurement window for each of a plurality of available channels; retaining a quantity of M of the plurality of received signal strength measurements for each of the plurality of available channels, wherein the quantity M is a value up to 25% of L; and assigning a channel metric denoted by m, to each of the plurality of available channels equal to:
  • ARRSI[j] is one of the received signal strength measurements
  • j is a received signal strength measurement index
  • . is an available channel index
  • I is a quantity of the plurality of available channels.
  • the invention can be characterized as a method, and means for accomplishing the method, of selecting between available channels, the method including the steps of: determining, for each of a plurality of available channels, a channel metric for each of a plurality of antennas corresponding to measurements taken at a receiver, the channel metric indicative of a level of interference received over each of the plurality of antennas; assigning an overall channel metric to each of the plurality of available channels based upon the channel metrics determined for each of the plurality of available channels; sorting the plurality of available channels according to their respective overall channel metric; determining whether co- channel signaling is present on an available channel having a lowest overall channel metric of the plurality of available channels; and selecting one of the plurality of available channels based upon at least the determining whether the co-channel signaling is present on the available channel having the lowest overall channel metric.
  • the invention can be characterized as a channel selection device for a communication terminal of a communication system comprising a dynamic selection module configured to perform the following steps: determining, for each of a plurality of available channels, a channel metric for each of a plurality of antennas corresponding to measurements taken at a receiver, the channel metric indicative of a level of interference received over each of the plurality of antennas; assigning an overall channel metric to each of the plurality of available channels based upon the channel metrics determined for each of the plurality of available channels; sorting the plurality of available channels according to their respective overall channel metric; obtaining an indication whether co-channel signaling is present on an available channel having a lowest overall channel metric of the plurality of available channels; and selecting one of the plurality of available channels based upon at least the determining whether the co- channel signaling is present on the available channel having the lowest overall channel metric.
  • FIG. 1 is a diagram illustrating interference between communicating terminals of adjacent cells of a communication system
  • FIG. 2 is a diagram illustrating adjacent channel interference between the communicating terminals of the adjacent cells of the communication system of FIG 1.
  • FIG. 3A is a functional block diagram of several components of a receiver of a communication terminal, e.g., an access point of FIG. 1, which according to several embodiments of the invention, implements a dynamic channel selection algorithm for selecting one of many available channels for communications with other communication terminals;
  • FIG. 3B is a functional block diagram of several components of another embodiment of the receiver of FIG. 3A which according to several other embodiments of the invention, implements the dynamic channel selection algorithm for selecting one of many available channels for communications with other communication terminals;
  • FIG. 4 is a flowchart illustrating one embodiment of the steps of the dynamic channel selection algorithm which may be performed by the receiver of FIG. 3A or FIG 3B;
  • FIG. 5 is a flowchart illustrating another embodiment of the steps of the dynamic channel selection algorithm of another embodiment of the invention.
  • FIG. 6 is a diagram illustrating interference between adjacent communication cells in which each access point in a communication cell has multiple receive antennas.
  • FIG. 7 A is a functional block diagram of several components of a multi-antenna receiver of a communication terminal, e.g., an access point of FIG. 6, which according to several embodiments of the invention, implements a dynamic channel selection algorithm for selecting one of many available channels for communications with other communication terminals;
  • FIG. 7B is a functional block diagram of several components of another embodiment of the receiver of FIG. 7A which according to several embodiments of the invention, implements the dynamic channel selection algorithm for selecting one of many available channels for communications with other communication terminals;
  • FIG. 8 is a flowchart illustrating one embodiment of the steps of the dynamic channel selection algorithm which may be performed by the receiver of FIG. 7A or FIG. 7B for communications between various remote terminals and the access point; and
  • FIG. 9 is a flowchart illustrating another embodiment of the steps performed by the receiver of FIG. 7A or FIG. 7B when implementing the dynamic channel selection algorithm of another embodiment of the invention.
  • FIG. 1 a diagram is shown illustrating interference between communicating terminals of adjacent communication cells. Illustrated are two cells 102 and 104, cell 102 including access point 1 (API), and cell 104 including access point 2 (AP2). API communicates with remote terminal 1 (RT1) in cell 102, while in cell 104, AP2 communicates with remote terminal (RT2). Each access point, API and AP2 may potentially use the same channel (for example, the same frequency channel, time channel and/ or code channel) or adjacent channels for uplink and downlink transmissions.
  • API access point 1
  • AP2 access point 2
  • Each access point, API and AP2 may potentially use the same channel (for example, the same frequency channel, time channel and/ or code channel) or adjacent channels for uplink and downlink transmissions.
  • Each of the cells 102, 104 may comprise communication cells in a wireless indoor network or a terrestrial cellular network. Focusing on the activity within cell 102, let AP1-RT1 denote a desired transmitter-receiver pair. Furthermore, in one embodiment, API and RT1 transmit packets using a Time Division Multiple Access/ Time Division Duplex (TDMA/TDD) scheme within cell 102; however, in other embodiments, API and RT1 may communicate using any known multiplexing scheme. As is illustrated by arrows 106 and 108, AP2 and RT2 in cell 104 cause interference during downlink/ uplink transmissions of the terminals in cell 102.
  • TDMA/TDD Time Division Multiple Access/ Time Division Duplex
  • AP2 potentially causes interference 108 during its downlink transmission 112 destined for RT2 on communications 110 between API and RT1.
  • RT2 potentially causes interference 106 on the communications 110 in cell 102 during its uplink transmissions 114 destined for AP2.
  • This interference illustrated as arrows 106 and 108 may be either co-channel interference or adjacent channel interference.
  • the interference 106, 108 is a large source of impairment that degrades performance in the wireless links of cell 102. Interference is especially problematic in a dense deployment environment, such as illustrated, where adjacent cells are in close proximity.
  • ACI adjacent channel interference
  • CCI co-channel interference
  • ACI is due, at least in part, to energy leakage from a signal transmitted in a channel adjacent to a channel selected by the AP.
  • CCI is due to in-band energy received from another transmitter, e.g. another AP or RT, in the vicinity using, for example, the same frequency channel, time channel (e.g., TDM A channel) and/ or code channel (e.g., CDMA channel) for its operation.
  • a dynamic channel selection (DCS) algorithm is provided at a given communication terminal (e.g.
  • the DCS algorithm's channel selection criteria is based upon not only the level of interference, but also the make up of the interference on each available channel.
  • the cells 102, 104 of FIG. 1 represent a wireless indoor (or indoor/ outdoor) local area network using orthogonal frequency divisional multiplexed (OFDM) communications based on the IEEE 802.11a standard or the HiperLAN2 standard.
  • OFDM orthogonal frequency divisional multiplexed
  • the dynamic channel selection algorithms of several embodiments of the invention may be applied in communication systems utilizing any single carrier or a multicarrier (one example of which is OFDM) transmission scheme.
  • the cells 102, 104 represent residential wireless networks in which the access points are to other computer networks, for example, a cable interface or a satellite interface to an Internet (e.g., within a set-top box), while the remote terminals comprise computers (PCs), laptops, televisions, stereos, appliances, palm devices, appliances, etc.
  • the cells 102, 104 represent wireless local area networks in an office or business in which the access points are coupled to larger computer networks and the remote terminals comprise other computers, laptops, palm devices, televisions, appliances, etc.
  • the cells 102, 104 represent wireless terrestrial cellular networks in which the access points comprise base stations and the remote terminals comprise wireless mobile devices. It is noted that in many embodiments, many of the communicating terminals are mobile. It is understood that the dynamic channel selection algorithm of several embodiments of the invention may apply to any wireless communication network, e.g., cellular, satellite, optical, short range, long range, indoor/ outdoor, in which interference is present and/ or channel conditions vary or fluctuate.
  • any wireless communication network e.g., cellular, satellite, optical, short range, long range, indoor/ outdoor, in which interference is present and/ or channel conditions vary or fluctuate.
  • the Dynamic Channel Selection (DCS) algorithm as disclosed herein may be applied to select a desirable channel regardless of the type of channel a communication system operates under.
  • the DCS algorithm is utilized to select an available frequency channel in communication systems that have multiple available frequency channels for communications (e.g., in an OFDM system).
  • the DCS algorithm is utilized to select an available time channel (or time slot) in communications systems that have several available time channels to select from (e.g., in TDMA systems).
  • the DCS algorithm is utilized to select an available code channel in communication systems that have multiple available code channels to select from (e.g., in CDMA systems).
  • the term channel generically refers to frequency channels, time channels, code channels, etc.
  • one or more of the remote terminals within each cell support communications having different QoS requirements, i.e., one or more of the remote terminals support different types of traffic, such that the different communications have different requirements in terms of the signal-to-interference ratio (SIR) or signal-to-noise ratio (SNR) required to be achieved at the receiver.
  • SIR signal-to-interference ratio
  • SNR signal-to-noise ratio
  • each of the remote terminals RT1 and RT2 supports one or more of data, voice, and video traffic, for example.
  • the channel selection algorithm of several embodiments of the invention may be used between any two communicating devices, without requiring that such devices be a part of a network or a cell.
  • the channel selection algorithm may be used in any system having two transceivers.
  • FIG. 2 shown is energy leakage 206 from an adjacent frequency channel 204 into a desired frequency channel 202.
  • This leakage 206 is often due to usage of non-ideal RF filters at a receiver input after reception by an antenna. Reducing this leakage 206 is often prohibitively expensive because sharp (high order) analog RF filters used to prevent the leakage 206 are expensive to build.
  • the leakage 206 illustrated in FIG. 2 is typical of ACI that results from non-ideal RF analog filtering.
  • a Physical (PHY) layer specification of each communication standard defines the maximum acceptable adjacent channel interference level.
  • the IEEE 802.11a PHY specification requires that for Binary
  • BPSK Phase Shift Keying
  • an adjacent channel interferer with a signal level of maximum 16 dB stronger should cause no more than 10% packet error rate.
  • the signal level in a desired available channel should be no less than 16 dB weaker than the adjacent channel signal.
  • this limit is 20 dB, i.e., even if the signal level in the desired band is 20 dB weaker than the adjacent channel signal, the packet error rate should not be more than 10%.
  • FIG. 3A is a functional block diagram of several components of a receiver 300 of a communication terminal, e.g., an access point of FIG. 1, which according to several embodiments of the invention, implements a dynamic channel selection algorithm for selecting one of many available channels for communications with other communication terminals.
  • FIG. 4 is a flowchart illustrating one embodiment of the steps of the dynamic channel selection algorithm which may be performed by the receiver of FIG. 3A or FIG. 3B.
  • the receiver 300 including an antenna 302, a radio frequency/ intermediate frequency integrated circuit device 304 (hereinafter referred to as the RF/IF IC device 304) that comprises a tuner 305, a radio frequency to intermediate frequency downconverter 306 (hereinafter referred to as the RF/IF downconverter 306), an IF to baseband downconverter 308, an analog to digital (A/D) converter 322, an auxiliary analog to digital (A/D) converter 320 and an Analog Received Signal Strength Indication (ARSSI) portion 310 (also referred to generically as a received signal strength module 310).
  • the RF/IF IC device 304 that comprises a tuner 305, a radio frequency to intermediate frequency downconverter 306 (hereinafter referred to as the RF/IF downconverter 306), an IF to baseband downconverter 308, an analog to digital (A/D) converter 322, an auxiliary analog to digital (A/D) converter 320 and an Analog Received Signal Strength In
  • a baseband integrated circuit device 312 also referred to as the baseband IC device 312 coupled to the RF/IF IC device 304 that comprises a demodulator 314, a preamble detector 315 (also referred to generically as a "co-channel signal detector”), a dynamic channel selection module 316 (also referred to as the DCS module 316), and an available channel select signal 318.
  • the antenna 302 may be implemented within the RF/IF IC device 304.
  • the receiver 300 Upon power-up of the AP, the receiver 300 needs to select a channel for use out of the available channels in an operating band. This process undertaken by the receiver 300 is called initial DCS (IDCS).
  • IDCS initial DCS
  • the initial DCS algorithm at the receiver 300 is employed to avoid selecting occupied channels (or more precisely, any available channel with poor quality) and ensure a uniform spreading of the devices over all the available channels.
  • the AP After the Initial DCS algorithm is carried out by the receiver 300, and an available channel is selected, the AP starts its normal operation using the selected channel for communications with other terminals. In several embodiments, however, the AP will monitor the quality of the selected channel and will initiate the DCS algorithm in the event the quality of the selected channel deteriorates. This process is called Ongoing DCS (ODCS). Ongoing DCS ensures using the best operating available channel with minimum level of interference, during the entire operation of the AP.
  • ODCS Ongoing DCS
  • the DCS module 316 Upon power-up of the AP, the DCS module 316 starts by sending a command, e.g., the available channel select signal 318 to the tuner 305 to tune into a first of the available channels (e.g., a first of available frequency, time, or code channels).
  • received signal strength measurements of the signals e.g., Analog Received Signal Strength Indication (ARSSI) measurements of the signals
  • ARSSI Analog Received Signal Strength Indication
  • the RF/IF downconverter 306 receives the signals and converts the signals to intermediate frequency signals
  • the intermediate frequency signals are provided to the received signal strength module 310.
  • the received signal strength module 310 (also coupled to the auxiliary A/D converter 320) then takes Analog Received Signal Strength Indication (ARRSI) measurements ⁇ (generically referred to as received signal strength measurements) of the intermediate frequency signals. These received signal strength measurements are provided to the auxiliary A/D converter 320 and are converted to digital representations of the received signal strength measurements (generally referred to a received signal strength measurements). The digital representations of the received signal strength measurements are indicative of the level of interference of the available channel and are provided from the auxiliary A/D converter 320 to the DCS module 316. The same process of tuning to an available channel and collecting measurements is repeated for all available channels. Thus, a plurality of received signal strength measurements are taken for each of the plurality of available channels (Step 402 of FIG.4).
  • ARRSI Analog Received Signal Strength Indication
  • the DCS module 316 will take every Kth one out of L total discrete received signal strength measurements taken at the received signal strength module 310. Denoting N (in milliseconds) as the size of the measurement window taken by the received signal strength module 310, and a total number of L discrete measurements taken at the received signal strength module 310 assuming that ARSSI measurements are updated every 1 ⁇ s , the number of received signal strength measurements input to the DCS module 316 is:
  • the received signal strength module 310 instead of taking one discrete measurement out of every K discrete measurements, the received signal strength module 310 averages a small number (e.g., K) of the L discrete received signal strength measurements to provide a single average measurement which is input to the DCS module 316.
  • the number of discrete measurements that are averaged may be within a range from one to sixteen discrete measurements. For example, if every four discrete measurements are averaged during the measurement window of N milliseconds, 250 times N single average measurements may be calculated. In some embodiments, a measurement window of approximately 1 millisecond is utilized and 250 of these single average measurements (derived from 1000 discrete measurements) are retained as received signal strength measurements input to the DCS module 316. While the received signal strength module 310 in the present embodiment calculates single average measurements from the discrete received signals strength measurements, one of ordinary skill in the art recognizes that this functionality may be performed elsewhere, e.g., by the DCS module 316.
  • the received signal strength measurements utilized by the DCS module 316 correspond to the discrete measurements taken at the received signal strength module 310.
  • the received signal strength measurements used by the DCS module 316 are all of the discrete received signal strength measurements (i.e., K-l) taken, and in other embodiments, the received signal strength measurements utilized by the DCS module 316 are a subset of the total number of L discrete received signal strength measurements taken (i.e., K>1), and in yet other embodiments, each received signal strength measurement utilized by the DFS module is an average of a small number of the L discrete received signal strength measurements taken at the received signal strength module 310.
  • a channel metric for the first available channel is derived (e.g., at the DCS module 316) from the received signal strength measurements taken over that first available channel. This channel metric is indicative of a level of interference present in the available channel. Similarly, channel metrics for other available channels are derived from their respective received signal strength measurements. Thus, a channel metric for each of the plurality of available channels based on the received signal strength measurements is determined (Step 404 of FIG. 4), the channel metrics indicative of the level of interference present in the available channels.
  • the DCS module 316 when determining the channel metric for a given channel, retains the M largest measurements (e.g., 32 of the largest measurements) of the number of received signal strength measurements (taken from a given available channel) that are provided to the DCS module 316 from the received signal strength module 310. The DCS module 316 then computes a channel metric for that available channel by averaging these M largest measurements. It should be recognized that the M largest received signal strength measurements retained by the DCS module 316 may be the M largest of discrete received signal strength measurements received at the DCS module 316 or may be the M largest of averaged received signal strength measurements received at the DCS module 316.
  • the M largest received signal strength measurements retained by the DCS module 316 may be the M largest of discrete received signal strength measurements received at the DCS module 316 or may be the M largest of averaged received signal strength measurements received at the DCS module 316.
  • a channel metric m for available channel i is defined in the following manner:
  • M denotes the M largest ARSSI measurements out of the received signal strength measurements utilized the DCS module 316, ; ' is an index of the M measurements and Max_ARSSI[j] is one of the retained received signal strength measurements where Max_ARSSI ⁇ M ⁇ denotes a vector of size M containing these M largest retained received signal strength measurements.
  • equation (2) above may be generally applied to systems having more than one available channel.
  • the number may vary depending on the system, number of channels, number of received signal strength measurements, etc.; however, the number M is generally small in comparison to the total number of received signal strength measurements.
  • M may be up to 25% of the total number (e.g., L) of discrete received signal strength measurements taken during the measurement window.
  • M is up to 20% of the total number of discrete received signal strength measurements.
  • M is up to 15% of the number of discrete received signal strength measurements, and more preferably, M is up to 10% of the total discrete received signal strength measurements taken during the measurement window.
  • M need not fall within these ranges in order to obtain a useful channel metric, but when M is within one of the ranges set forth above, the resulting channel metrics will provide a more accurate representation of the level of interference on the available channels. More particularly, M will provide a more accurate picture of an interference level that may indicate the presence of a minimum interfering co-channel signal on the available channel (e.g., a beacon transmitted by another terminal that may only occupy a small portion (e.g., 10%) of the measurement window).
  • a minimum interfering co-channel signal on the available channel e.g., a beacon transmitted by another terminal that may only occupy a small portion (e.g., 10%) of the measurement window.
  • the M received signal strength measurements are retained out of L/K signal strength measurements that are received by the DCS module 316.
  • M times K may be up to 25% of L, and in some embodiments, M times K is up to 20% of . Preferably, however, M times K is up to 15% of L, and more preferably, M times K is up to 10% of L. Accordingly, in one embodiment, for a measurement window of 1 msec, M is selected to be 32 out of the 1000 ( ) measurements taken during the 1 msec window by the received signal strength module (assuming updates every 1 ⁇ s ). Thus, M is 3.2% of L measurements, which fits within the above recited percentage ranges.
  • a median curve for each available channel indicative of the received signal strength over each available channel is established, and this curve is translated into a channel metric for each available channel.
  • This histogram-based method is well known in the art, and is disadvantageous in many systems (e.g., synchronous media access control (MAC) systems) because the histogram is utilized to provide an overall average of the noise of the MAC frame and when ARSSI measurements are taken, typically only 10% of the MAC frame is utilized as a beacon.
  • MAC synchronous media access control
  • the M largest received signal strength measurements are more likely to produce more accurate measurements of co-channel signals (e.g., a beacon) rather than background noise. This is because background noise is more likely to be a smaller component of the average of the M largest measurements than an average of all or a larger number of received signal strength measurements.
  • the quantity M is selected so that the M received signal strength measurements (either discrete or averaged) corresponding to the discrete measurements taken at the received signal strength module 310 will be measurements that fall within a minimum co- channel signal (e.g., a beacon) occupying a portion of the measurement window (e.g., about 10% of the measurement window).
  • the specific percentage ranges of M as described above are based upon the size of a beacon such that M is preferably less than or equal to the number of received signal strength measurements that may be taken during the duration of such a beacon.
  • the DCS module 316 After determining the channel metrics m i for all the available channels, the DCS module 316 proceeds by sorting the plurality of available channels according to their respective channel metrics (Step 406 of FIG. 4). In one embodiment, the available channels are sorted by their respective channel metrics in ascending order.
  • the set of unsorted available channels is represented mathematically by UM ⁇ 7 ⁇ which denotes a vector of unsorted channel metrics of size 7 defined as: mi m ....mi] where is the number of available channels.
  • CM[1] is the minimum channel metric of the available channels
  • CM[7] is the maximum channel metric of the available channels.
  • CI[1] is the available channel having the minimum channel metric
  • CI[7] is the available channel having the maximum channel metric
  • a randomization process is utilized to establish which of the available channels having the minimum channel metric is indexed as CI[1].
  • CI[1] when an available channel indexed by CI[1] has no co-channel signal present on it, that available channel CI[1] is chosen for communications.
  • channel 1 and channel 2 both have the minimum channel metric, it is possible that channel 1 will be always selected as a communications channel (assuming there is no co-channel signaling present in either of these two channels).
  • the indexed order of the available channels having the minimum channel metric are shuffled randomly. For example, when there are two available channels that have the minimum channel metric, e.g., channel 1 and channel 2, each available channel having the minimum channel metric is assigned a 50% probability of being assigned as CI[1]. In this way, channel 2 for example, has a 50% chance of being assigned the position of CI[1].
  • the randomization process is utilized to generate a random order of the available channel indexes.
  • channels 1, 4, and 6 each have the minimum channel metric and are indexed as CI[1], CI[2], and CI[3] respectively before the randomization process
  • their order in the sorted channel metric might change depending upon the outcome of the randomization process.
  • channel 6 potentially may be indexed as CI[1] instead of its previous index of CI[3] and channels 1 and 4 may be indexed as CI[2] and CI[3] respectively.
  • each of the three channels having the minimum channel metric has a 33.3% chance of being assigned the position of CI[1].
  • the incorporation of the randomization process in the sorting step of the DCS algorithm further enhances the uniform spreading of the devices on all available channels because the potential exists for multiple channels having the minimum channel metric to be utilized for communications .
  • the DCS module 316 determines whether the channel metric of the available channel having the lowest channel metric of the available channels, i.e., CM[1], is greater than an upper threshold (UT) (Step 408 of FIG. 4). In several embodiments, Step 408 of FIG. 4 is not performed or the upper threshold is ignored and the DCS module 316 continues to analyze the available channel having the lowest channel metric of the available channels without comparing it against a threshold.
  • RPC rate and power control
  • API and AP2 are configured to provide both RPC and DCS algorithms, ignoring the upper threshold is often a viable approach because RPC and DCS algorithms may be tightly tied together, and it can be expected that after an access point e.g., API, selects an available channel which is used by another AP, e.g., AP2, in the near vicinity, the RPC algorithm will engage and then both AP's, e.g., API and AP2, will try to adjust their rates and powers to maximize the throughput and minimize the interference in the system.
  • RPC rate and power control
  • a threshold it is reasonable to continue with the DCS algorithm even if a threshold is exceeded. In other embodiments, however, it is desirable to have at least one available channel having a channel metric below an upper threshold.
  • One possible solution is to continue searching for an available channel having a channel metric below the upper threshold by once again taking a plurality of received signal strength measurements for each of the available channels (Step 402 of FIG. 4), i.e., starting the process of selecting an available channel over again until an available channel having a channel metric that meets the threshold is detected.
  • a user interface may display a message such as "Searching ", to indicate to the user that an available channel is yet to be selected. This, however, could be very frustrating for the user and may result in long delays before selecting an available channel for communications.
  • a retry counter r is defined and set to zero when the DCS algorithm initiates. After all channel metrics have been determined, if the minimum channel metric, i.e., CM[1], is above an upper threshold and the retry counter is less than a prescribed maximum number of retries R , the DCS process is restarted again, i.e., the available channels will be probed again (Step 402 of FIG. 4).
  • This process will be repeated up to R times when the minimum channel metric exceeds the upper threshold, and if after R tries the minimum channel metric is still above the upper threshold, the available channel with the minimum channel metric will be selected.
  • RPC rate and power control
  • Step 408 of FIG. 4 a determination is made as to whether co-channel signaling is present on the available channel having the lowest channel metric (i.e. CI[1]) of the available channels.
  • co-channel signaling refers to other interfering communications received on the available channel CI[1] that are highly correlated with signals used by the present system, but are not generated by either the receiver 300 of the present system or the terminals it is intended to communicate with. These co-channel signals may be any other communication burst from another transmitter in the vicinity.
  • the co-channel signaling represents a co-channel interference that typically cannot be removed in the baseband processing as opposed to adjacent channel interference.
  • co-channel signaling may be found by correlating the received signal with a signature of a known signal.
  • a signal e.g., a signal from outside the present system
  • a desired signal of interest in the present system is considered a co-channel signal if it is highly correlated with the desired signal. If two signals sharing the same channel are uncorrelated then they are not considered co-channel signals in this context.
  • Such an uncorrelated signal sharing the same channel with the signal of interest increases the system noise floor (i.e. reduces the effective signal to noise ratio in the channel). As long as the increase in the noise floor is within a specified threshold (as defined by industry standard), the system is likely to operate properly.
  • the determination as to whether co-channel signaling is present on CI[1] is made by the preamble detector 315.
  • the RF/IF downconverter 306 couples to the IF to baseband downconverter 308 and provides the intermediate frequency signals to the IF to baseband downconverter 308.
  • the IF to baseband downconverter 308 then converts the intermediate frequency signals to baseband signals and provides the baseband signals via coupling to the A/D converter 322.
  • the A/D converter 322 digitizes the baseband signals and provides the digitized baseband signals to the preamble detector 315.
  • the preamble detector 315 (coupled to the DCS module 316) provides a signal to the DCS module 316 indicating that a preamble is detected (i.e., the DCS module obtains an indication whether co-channel signaling is present on an available channel having a lowest channel metric of the plurality of available channels.) If no preamble is detected the lowest channel metric is chosen for communications.
  • Step 412 of FIG. 4 If there is no co-channel signaling present on the available channel having the lowest channel metric (Step 412 of FIG. 4), then the available channel having the lowest channel metric is selected for communications (Step 414 of FIG. 4). This selection is made because when there is no co-channel signaling on the available channel having the lowest channel metric (i.e., available channel CI[1]) no other available channel will have a level of interference that can be reduced below the level of interference present on CI[1].
  • the DCS algorithm advantageously distinguishes between co-channel interference and adjacent channel interference which allows the receiver 300 to make a more "intelligent" decision about whether to use CI[1] for communication than prior art methods.
  • the DCS module 316 is able to determine if the interference on CI[1] is solely adjacent channel interference, and if so, then to select CI[1].
  • a prior art receiver may pick an available channel CI[1] having co-channel interference (CCI) that cannot be filtered to a level that is below another available channel having only adjacent channel interference (ACI), or a combination of CCI and ACI.
  • CCI co-channel interference
  • ACI adjacent channel interference
  • the determination as to whether co- channel signaling is present on CI[1] may be made by identifying a particular known signature of the co-channel signaling.
  • the preamble detector 315 may be replaced with a signature detector module to identify the anticipated signature of the co-channel signaling.
  • Step 412 of FIG. 4 If co-channel signaling is detected on the available channel having the lowest channel metric (Step 412 of FIG. 4)(e.g., a PHY preamble is detected on CI[1]), then a comparison of the channel metric of the available channel having the lowest channel metric with a channel metric of an available channel having a higher channel metric is made (Step 416 of FIG. 4). This comparison is made because, as discussed above, baseband filtering can remove adjacent channel interference, but cannot effectively remove co- channel interference.
  • CI[1] is compared with other available channels starting from available channel CI[2] to determine if the difference between the channel metric of all the other available channels have channel metrics that are greater than the channel metric of CI[1] by more than a prescribed threshold above CM[1].
  • the prescribed threshold depends upon the effectiveness of baseband processing to filter adjacent channel interference from available channels having a higher channel metric than CI[1].
  • the prescribed threshold is about 10-15 dB so that available channels having a channel metric greater than the channel metric of CI[1] by more than about 10-15dB have a channel metric that is greater than CI[1] by more than the prescribed threshold.
  • CI[1] is selected as an available channel for communications (Step 420 of FIG. 4).
  • the reason for such a selection is that, (at this stage) it is known that available channel CI[1] has co-channel signaling (as opposed to having only adjacent channel signaling) present that cannot be filtered out, but only a prescribed amount of adjacent channel interference (ACI) will be removed by the digital baseband filtering from available channels having a higher channel metric than CI[1].
  • ACI adjacent channel interference
  • CI[1] is no longer the best candidate. This is because baseband filtering can filter out the adjacent channel interference up to about the prescribed threshold (which in several embodiments is about 10- 15dB). It is beneficial, therefore, to determine whether any of the available channels having a higher channel metric than CI[1] have co-channel signaling present on them. Thus, in several embodiments, when there is an available channel having a channel metric that is higher than CM [I] by less than the prescribed threshold (Step 418 of FIG.
  • the DCS algorithm determines whether co-channel signaling is present on the available channel having a higher channel metric (Step 422 of FIG. 4) than CI[1].
  • the determination as to whether co-channel signaling is present on the available channel having a higher channel metric may be made in a similar manner as the determination as to whether co-channel signaling is present on CI[1] described above.
  • the DCS algorithm provides advantages over the prior art (which only considered the magnitude of interference) because both the magnitude and the type of interference present on an available channel are factors used by the DCS algorithm that allow the receiver 300 to select an available channel that may be filtered to a lowest level of interference among the available channels.
  • the determination of whether co-channel signaling is present on an available channel having a higher channel metric than CI[1] involves the DCS algorithm determining, beginning with an available channel CI[2] and proceeding in order to the other available channels, whether co-channel signaling is present on each of the available channels having a channel metric greater than CM[1]. Once a particular available channel is found that does not have co-channel signaling present on it (and the particular available channel has signal activity that is no stronger than the signal activity of CI[1] by no more than the prescribed threshold) that particular available channel is selected for communications. As described above, co-channel signaling is signaling that is highly correlated with the signaling of the present system.
  • the determination as to whether co-channel signaling is present on other available channels having a higher channel metric than CI[1] comprises a determination as to whether a PHY preamble is present on the available channels having higher channel metrics.
  • the preamble detector 315 detects whether a preamble is present on the available channels having higher channel metrics than CI[1] in the same way the preamble detector 315 detects whether a preamble is present on CI[1] in the embodiment discussed above; thus, the DCS module 316 obtains an indication (e.g., a signal from the preamble detector 315) whether the preamble is present on the available channels having higher channel metrics.
  • the DCS algorithm selects the available channel with minimum interference, i.e., available channel CI[1], regardless of any co- channel signaling present on CI[1]. Thus, the DCS algorithm selects a channel for communications based upon whether the co-channel signaling is detected on the available channel having the higher channel metric (Step 424 of FIG. 4)(i.e., a higher channel metric than CI[1]).
  • the DCS algorithm selects an available channel for communications based upon one or more of the following criteria: (a) whether co-channel signaling is present on the available channel having the lowest channel metric; (b) the difference between the available channel having the lowest channel metric and the available channel having a higher channel metric; and (c) whether co-channel signaling is detected on the available channel having a higher channel metric.
  • the DCS algorithm is applied both to provide an Initial DCS (IDCS) at the time during which the AP is powered- up, and to provide Ongoing DCS (ODCS) during the AP operation.
  • IDCS Initial DCS
  • ODCS Ongoing DCS
  • all terminals in the given cell stop communicating so that received signal strength measurements may again be taken, and the same process for selecting one of the available channels is carried out as discussed above.
  • the reasons for the ODCS process to engage may be high error rates, a large number of cyclic redundancy check (CRC) errors, or retransmissions.
  • CRC cyclic redundancy check
  • One or a collection of these parameters may be used at the AP to decide whether the AP should enter the DCS mode again to find a better available channel to avoid further deterioration of the system throughput in the immediate future.
  • the DCS operation will be entirely handled by the AP, and no assistance will be provided by the RTs for the ODCS process.
  • provisions in the media access control (MAC) design may be made to facilitate the participation of RTs in the ODCS process to assist the AP in finding the best available channel to move to.
  • the AP delegates to the RT the process of making measurements on other available channels.
  • the RT then sends a report back to the AP at the end of the measurement process. During this time, the AP will not schedule any traffic to this delegated RT.
  • This kind of DCS process is denoted as RT Assisted DCS (RADCS).
  • RADCS RT Assisted DCS
  • FIG. 3B shown is a functional block diagram of several components of another embodiment of the receiver of FIG. 3 A, which according to several other embodiments of the invention, implements the dynamic channel selection algorithm for selecting one of many available channels for communications with other communication terminals.
  • the receiver 350 including the antenna 302, a radio frequency/ baseband frequency integrated circuit device 326 (hereinafter referred to as the RF/BB IC device 326) that comprises the tuner 305, a radio frequency to baseband frequency downconverter 324 (hereinafter referred to as the RF/BB downconverter 324), the analog to digital (A/D) converter 322, the auxiliary analog to digital (A/D) converter 320 and the Analog Received Signal Strength Indication (ARSSI) portion 310 (also referred to generically as the received signal strength module 310).
  • RF/BB IC device 326 that comprises the tuner 305
  • a radio frequency to baseband frequency downconverter 324 hereinafter referred to as the RF/BB downconverter 324
  • the analog to digital (A/D) converter 322 the auxiliary analog to digital (A/D) converter 320
  • the Analog Received Signal Strength Indication (ARSSI) portion 310 also referred to generically as the received signal strength module 310
  • the baseband integrated circuit device 312 also referred to as the baseband IC device 312 coupled to the RF/BB IC device 326 that comprises the demodulator 314, the preamble detector 315 (also referred to generically as the "co-channel signal detector"), the dynamic channel selection module 316 (also referred to as the DCS module 316), and the available channel select signal 318.
  • the antenna 302 may be implemented within the RF/BB IC device 326.
  • the receiver 350 in several embodiments, operates in much the same way as the receiver 300 of FIG. 3A; however, the signals from the tuner 305 are received by the RF/BB downconverter 324 and converted directly to baseband frequency instead of being converted to an intermediate frequency.
  • the RF/ BB downconverter 324 provides the signals at baseband frequency to the received signal strength module 310 where received signal strength measurements are taken of the signals at baseband frequency instead of at an intermediate frequency.
  • the receiver 350 may be referred to as a zero IF receiver.
  • the baseband signals from the RF/BB downconverter 324 are provided directly to the A/D converter 322.
  • baseband signals from the RF/BB downconverter 324 are provided to the A/D converter 322 where the baseband signals are digitized.
  • the digitized baseband signals from the A/D converter 322 are then provided to the preamble detector 315 where the determination as to whether co-channel signaling is present on a particular channel is made in accordance with the steps set forth in FIG. 4.
  • receivers 300, 350 of FIG. 3 A and FIG. 3B may be implemented as a set of instructions that are performed in dedicated hardware, firmware or in software using a processor or other machine to execute the instructions to accomplish the provided functionality.
  • the receivers 300, 350 of FIG. 3A and FIG. 3B may be implemented as one or more integrated circuit (IC) devices.
  • IC integrated circuit
  • the antenna 302, the tuner 305, the RF/IF downconverter 306, the IF to baseband downconverter 308, the auxiliary A/D converter 320, the A/D converter 322, and the received signal strength module 310 are implemented on the RF/IF IC device 304, while the remaining functional components of the receiver, including the DCS module 316 are implemented on the baseband IC device 312, which is coupled to the RF/IF IC device 304.
  • a zero IF architecture e.g., the embodiment of FIG.
  • the antenna 302, the tuner 305, the RF/BB downconverter 324, the auxiliary A/D converter 320, the A/D converter 322, and the received signal strength module 310 are implemented on the RF/BB IC device 326, while the remaining functional components of the receiver 350, including the DCS module 316 are implemented on the baseband IC device 312, which is coupled to the RF/BB IC device 326.
  • These integrated circuit devices 304, 326 and 312 may be referred to application specific integrated circuits (ASICs) or generically as chips.
  • the RF/IF IC device 304, the RF/BB IC device 326 and the baseband IC device 312 may be implemented as a single chip or ASIC.
  • the RF/IF IC device 304, the RF/BB IC device 326 and the baseband IC device 312 may be a part of a chipset or a single chip or ASIC designed to implement the function blocks of the receivers 300, 350.
  • the steps of FIG. 4 may be performed as a set of instructions that are performed in dedicated hardware, firmware or in software using a processor or other machine to execute the instructions to accomplish the given steps.
  • FIG. 5 shown is a flowchart illustrating the steps performed by the access point of FIG. 3A or FIG. 3B in implementing the DCS algorithm for selecting between available frequency channels in accordance with one embodiment of the present invention.
  • the nominal carrier frequency f c corresponds to its carrier number, N carr j er , which is defined as:
  • the nominal carrier frequencies are spaced 20 MHz apart, and all transmissions are centered on one of the nominal carrier frequencies.
  • the DCS algorithm is employed to avoid occupied frequency channels at a time of power-up and to ensure a uniform spreading of 5 GHz devices over all the available channels.
  • Ongoing DCS ensures that the best operating frequency channel is used with the minimum level of interference during the entire operation of the AP.
  • DCS operation initially avoids occupied frequency channels that have a high level of interference at the time of power-up, and Ongoing DCS minimizes the interference in the system by moving to the appropriate available channel during operation of the system. Such operation will support high density deployments for the 5 GHz wireless devices.
  • the DCS algorithm Upon power-up, the DCS algorithm is started (Step 502), and the channel index i is set to 1 (Step 504). If the channel index z is not greater thaneight (Step 505), an available channel is selected by tuning (e.g., with the tuner 305 of FIG. 3) to that available channel (Step 506) and a DCS measurement window of size N milliseconds is opened (Step 508). In several embodiments, received signal strength measurements are collected over the available channel i during a measurement window of about 2 milliseconds. These measurements are taken by the received signal strength module 310 of FIG. 3, for example.
  • discrete received signal strength measurements are utilized, and using equation (1), the number of received signal strength measurements used to assist the DCS algorithm, assuming one out of every K measurements are input to the DCS module 316, a 2 millisecond measurement window is utilized and assuming received signal strength measurements are updated every 1 ⁇ s is: 2000/ K.
  • every four discrete received signal strength measurements are averaged to provide 500 received signal strength measurements that are each an average of four discrete received signal strength measurements. It should be recognized, however, that the time period allocated for the measurement window (Step 508) may vary depending upon the size of the MAC frame, but preferably the measurement window N is at least the size of the MAC frame.
  • a channel metric for this first available channel is determined by averaging these M largest measurements using equation (2) (Step 512). The same process of tuning to an available channel, collecting measurements, and finally determining the channel metric will be repeated for all 7 available channels, e.g, all eight available channels.
  • Step 514 the channel index i is incremented by one (Step 514), and Steps 506 through 514 are repeated until - > 7 (e.g., until - > 8) (Step 505), at which point a channel metric will have been determined for each of the available channels. It is noted that other methods may be used to determine the channel metric , for each available channel, as described herein. Thus, Steps 504 through 514 represent one embodiment of accomplishing steps 402 and 404 of FIG. 4. After gathering the channel metrics for all the eight available channels, the DCS algorithm proceeds by sorting the available channels by their respective channel metrics in ascending order (Step 516).
  • the DCS algorithm compares the CM[1] element, which is the available channel with the minimum channel metric (also referred to as the QUIETEST channel, among all the eight available channels) against an upper threshold (UT) (Step 520). If the signal activity in the QUIETEST channel is above the upper threshold, this means that none of the available channels are "interference free enough" to be selected, and in one embodiment, a retry counter (that is set to zero upon initiation of the DCS algorithm) is incremented by one (Step 518). If the retry counter is less than a predetermined maximum number of attempts R (Step 519), the DCS process is restarted again (Step 502), i.e., the available channels will be probed again.
  • a retry counter that is set to zero upon initiation of the DCS algorithm
  • Step 524 the available channel with the minimum channel metric, i.e. CI[1] is selected for communications. If CM[1] is not greater than the upper threshold (UT) (Step 520), then a determination is made as to whether a PHY preamble can be detected on available channel CI[1] (Step 522), i.e., it is determined if co-channel signaling is present on CI[1].
  • Step 522 If a preamble is not detected (Step 522), it means that, probably this is not a co-channel signal (but there might be a non 802.11a device in the same band), and available channel CI[1] is selected (Step 524). If a PHY preamble is detected on available channel CI[1] (Step 522), then the DCS algorithm starts searching for an available channel having a higher channel metric with an acceptable level of interference that does not have a preamble (i.e., one example of a co-channel signal) on it (Step 526).
  • a preamble i.e., one example of a co-channel signal
  • the first step in the search for such an available channel is to compare available channel CI[1] with the other available channels starting from available channel CI[2] by subtracting the channel metric of CI[1], i.e., CM[1], from the channel metrics of the available channels with higher channel metrics starting with CI[2] (Step 528).
  • the next test is to check whether signal activity in available channel CI[2] is stronger than signal activity in available channel CI[1] by more than a threshold of approximately 10 dB (Step 530). The reason for this comparison is that, at this stage, it is known that CI[1] is a co-channel signal with signal activity less than available channel CI[2].
  • CM[2]-CM[1]>10 dB available channel CI[1] is selected (Step 524) even though the source of interference on CI[1] is a co-channel signal because, even if the source of interference in CI[2] was due to adjacent channel signal, the baseband filtering cannot further reduce it below CM[1].
  • CM[2] is not greater than CM[1] by more than about 10 dB (Step 530)
  • Steps 536 because (at this stage) it is known that the interference on CI[2] is from ACI and that baseband filtering can reduce the ACI interference on CI[2] below the interference level on CI[1]. Otherwise, if a preamble is detected on available channel CI[2] (Step 534), the search continues by incrementing the channel index (Step 538) to find an available channel without co-channel signaling that has signal activity that is not greater than about lOdB more than that of CI[1]. This continuing search involves repeating Steps 528 through 540 as necessary while the channel index i less than eight (Step 540).
  • the DCS algorithm selects the available channel with the minimum level of interference, available channel CI[1] (Step 524).
  • the DCS algorithm continues to monitor the communications taking place for a DCS triggering event as part of an Ongoing DCS (ODCS) operation (Step 542).
  • DCS triggering events include high error rates, a large number of CRC errors, or retransmissions.
  • One or a collection of these parameters may be used at the AP to trigger the start of the DCS algorithm again (Step 502) to find a better available channel to avoid further deterioration of the system throughput in the immediate future.
  • the steps of the DCS algorithm shown with reference to FIG. 5 in several embodiments are handled by the AP, without assistance from the RTs.
  • provisions may be made in MAC design to facilitate the participation of RTs in the ODCS process to assist the AP in finding the best available channel to move to.
  • the AP will give delegation to the RT to go and make measurements on other available channels and send a report back to the AP at the end of the measurement process. During this time, the AP will not schedule any traffic to this delegated RT.
  • Such a process may be referred to as RT Assisted DCS (RADCS).
  • steps listed in FIG. 5 generally represent the steps in performing the DCS algorithm according to several embodiments of the invention. These steps may be performed by the DCS module 316 of FIG. 3 A or FIG. 3B and/ or may be performed as a set of instructions that are performed in dedicated hardware, firmware or in software using a processor or other machine to execute the instructions to accomplish the given steps. It is also noted that the steps listed in FIG. 5 are adaptable to apply to selection of channel types other than frequency channels. One of ordinary skill in the art is readily able to adapt the steps of FIG. 5 so as to apply to systems in which a selection of, for example, either time channels or code channels is desired. For example, in one embodiment, Steps 504, 505, 506 and 508 are varied depending on the type of channel being chosen.
  • FIG. 6 a diagram is shown illustrating interference between adjacent communication cells in which access points in each communication cell have multiple receive antennas. Shown are access points API and AP2 that each have six receive antennas arranged with a hexagonal geometry (labeled respectively as Ant-1, Ant-2, Ant-3, Ant-4, Ant- 5, and Ant-6) . As shown, API and AP2 are in close enough proximity to one another such that a signaling 610 transmitted between RT2 and AP2 is received at API as interference 608.
  • API and AP2 of FIG. 6 may operate, for example, in similar environments and in similar systems to API and AP2 described with reference to FIG. 1. Thus, API and AP2 of FIG. 6 potentially use the same channel or adjacent frequency channels for uplink and downlink transmissions in a wireless indoor network or a terrestrial cellular network. API and AP2 of FIG. 6, however, have multiple receive antennas allowing each access point API, AP2 to receive a signal with more than one antenna.
  • API when API powers up, it needs to select a different available channel for communications than the available channel selected by AP2.
  • the received signal strength (RSS) of interference 608 received at Ant-1 of API will be less than the RSS of interference 608 at Ant-4 of API.
  • RSS received signal strength
  • received signal strength measurements are utilized for establishing channel metrics and ranking the available channels so that a given AP can decide which is the best available channel to utilize. Therefore, if a default antenna such as Ant-1 of API is selected, and the DCS algorithm is utilized to sort the available channels and rank them only based on this one antenna, API may end up choosing an available channel for communications that is not optimal.
  • the DCS algorithm accounts for each available receive antenna before ranking the available channels.
  • FIG. 7A shown is a functional block diagram of several components of a multi-antenna receiver 700 of a communication terminal, e.g., an access point of FIG. 6, which according to several embodiments of the invention, implements a dynamic channel selection algorithm for selecting one of many available channels for communications with other communication terminals
  • FIG. 8 is a flowchart illustrating one embodiment of the steps of the dynamic channel selection algorithm which may be performed by the receiver of FIG. 7A or FIG. 7B for communications between various remote terminals and the access point.
  • a receiver 700 including antennas 702, 704, 706, 708, 710, 712, a radio frequency to intermediate frequency integrated circuit device 714 (hereinafter referred to as the RF/IF IC device 714) that comprises an antenna selector 716; tuner 718; radio frequency to intermediate frequency downconverters 722, 724 (hereinafter referred to as RF/IF downconverters 722, 724); analog to digital (A/D) converters 756, 758; IF to baseband downconverter portions 726, 728; a multiplexer 760; an auxiliary analog to digital (A/D) converter 762; and Analog Received Signal Strength Indication (ARSSI) portions 730, 731 (also referred to as a received signal strength modules 730, 731).
  • the RF/IF IC device 714 that comprises an antenna selector 716; tuner 718; radio frequency to intermediate frequency downconverters 722, 724 (hereinafter referred to as RF/IF downconverters 722, 724); analog
  • a baseband integrated circuit device 732 also referred to as the baseband IC device 732 that comprises demodulators 734, 738; preamble detectors 736, 740 (also referred to generically as “co- channel signal detectors”); and a dynamic frequency selection module 742 (also referred to as the DCS module 742). Additionally shown is a channel select signal 744 that couples the DCS module 742 and the tuner 718 and an antenna select signal 746 that couples the DCS module 742 and the antenna selector 716.
  • the receiver 700 of FIG. 7A supports Q receive antennas (e.g., antennas 702, 704, 706, 708, 710, 712) and n receiver chains (e.g., two receiver chains), each receiver chain including a respective RF/IF downconverter, a respective IF to baseband downconverter and a respective demodulator.
  • receiver chain #1 includes RF/IF downconverter 722, IF to baseband downconverter portion 726, A/D converter 756, and demodulator 734
  • receiver chain # 2 includes RF/IF downconverter 724, IF to baseband downconverter portion 728, A/D converter 758 and demodulator 738.
  • the receiver 700 receives signaling in two separate receive chains using two of the available receive antennas at any given time.
  • This architecture facilitates diversity combining at the receiver 700 in a communication mode which results in considerable diversity gain for decoding the received signal. Additional details regarding the operation and features of receiver 700 may be found in Patent Application No. 09,944,519 entitled METHOD FOR ESTIMATING CARRIER-TO-NOISE-PLUS- INTERFERENCE RATIO (CNIR) FOR OFDM WAVEFORMS AND THE USE THEREOF FOR DIVERSITY ANTENNA BRANCH SELECTION to Crawford et al., filed 11/26/01, Attorney Docket No. 70629.
  • more than one antenna is evaluated to determine an overall channel metric for each available channel (e.g., for each available frequency, time, and/or code channel) based on the measured received signal strength at each of the antenna elements evaluated. For example, in one embodiment, all available antenna elements are evaluated to determine an overall channel metric for each available channel.
  • the access point 700 takes a plurality of received signal strength measurements over each of Q antennas, taken n at a time, for each of a plurality of available channels (Step 802 of FIG. 8).
  • the process of taking the plurality of received signal strength measurements is initiated by the DCS module 742 which instructs the tuner 718 via an available channel select signal 744 to tune into a first of the available channels. Additionally, the DCS module 742 selects two particular antennas of the Q antennas (e.g., antennas 702, 704) by sending the antenna select signal 746 to the antenna selector 716. In this embodiment, based upon the antenna select signal 746 from the DCS module 742, the antenna selector 716 selects the two particular antennas to receive signaling over the first of the available channels.
  • the received signaling samples from two particular antennas are carried from the two particular antennas through the antenna selector 716 and through the tuner 718 to the RF/IF downconverters 722, 724.
  • the RF/IF downconverters 722, 724 each receive the signaling from a different path so that each of the RF/IF downconverters 722, 724 receives signaling from a different antenna.
  • the RF/IF downconverter 722 receives the signaling received at antenna 702
  • RF/IF downconverter 724 receives the signaling received at antenna 704.
  • the RF/IF downconverters 722, 724 (coupled to respective received signal strength modules 730, 731) then convert the two samples of the received signaling to two intermediate frequency signaling samples, and the intermediate frequency signaling is provided to the received signal strength modules 730, 731 where received signal strength measurements are taken for each of the two samples of the received signaling from the two particular antennas (e.g., antennas 702, 704).
  • the multiplexer 760 connects one of the received signal strength modules 730, 731 at a time to the auxiliary A/D converter 762 where the received intermediate frequency signaling samples are digitized and provided to the DCS module 742.
  • FIG. 7A illustrates one embodiment having an antenna selector 716 that selects two of the six available antennas 702, 704, 706, 708, 710, 712 to allow received signal strength measurements to be taken by the received signal strength modules 730, 731 for two antennas at the same time.
  • the DCS algorithm will accommodate receivers having a differing number of antennas Q, and will also accommodate receivers having only one receive chain or two or more receive chains so that one or more antennas may be accessed at the same time (i.e., generically, n may be greater than or equal to one).
  • a channel metric (also referred to as an antenna channel metric) is determined for each of the Q antennas taken n at a time that is based upon the received signal strength measurements (Step 804 of FIG. 8) from the particular antennas.
  • the channel metric established by the DCS module 742 may be based upon received signal strength measurements that are either discrete received signal strength measurements or an average of a small number (e.g., four) of discrete received signal strength measurements.
  • 3A, 3B and 4 to calculate a channel metric for each available channel is applied to each antenna element separately so that for each of the available channels, a separate channel metric is determined for each antenna element that is based upon the received signal strength measurements for that given channel and antenna.
  • These channel metrics are indicative of a level of interference seen over each available channel for each of the Q antennas.
  • the DCS module 742 retains the M largest received signal strength measurements and computes the channel metric for each antenna by averaging these M largest measurements.
  • M may be up to 25% of the total number (e.g., L) of discrete received signal strength measurements taken during the measurement window. In some embodiments, M is up to 20% of the total number of discrete received signal strength measurements. Preferably, however, M is up to 15% of the number of discrete received signal strength measurements, and more preferably, M is up to 10% of the total discrete received signal strength measurements taken during the measurement window.
  • the M received signal strength measurements are retained out of L/K signal strength measurements that are received by the DCS module 316.
  • the product of M and K i.e. M times K
  • M times K may be up to 25% of L, and in some embodiments, M times K is up to 20% of L.
  • M times K is up to 15% of L, and more preferably, M times K is up to 10% of L.
  • a two-dimensional channel metric m i q is defined as follows:
  • the channel metrics m ⁇ q may be determined using any known technique, e.g., using the histogram-based approach described above.
  • an overall channel metric m t is assigned by the DCS module 742 to each of the plurality of available channels based upon - the determined channel metrics m l q for each of the plurality of available channels (Step 806 of FIG. 8).
  • the overall channel metric for each of the available channels is assigned as the maximum antenna channel metric for each of the available channels.
  • the overall channel metric m, for an available channel i is defined as follows:
  • the overall channel metric for each of the available channels is assigned as the average of the antenna channel metrics for each of the available channels.
  • _i 7 1 where 7 is the number of available channels, i is the channel index, Q is the number of antenna elements, and q is the antenna index.
  • the DCS module 742 After assigning the overall channel metrics for all the available channels, the DCS module 742 proceeds by sorting the plurality of available channels according to their respective overall channel metrics (Step 808 of FIG. 8) in ascending order.
  • CM [1] is the minimum overall channel metric of the available channels
  • CM [7] is the maximum overall channel metric of the 7 available channels.
  • CI[1] is the available channel having the minimum overall channel metric
  • CI[7] is the available channel having the maximum overall channel metric.
  • a randomization process is utilized to randomly assign one of the available channels having the minimum overall channel metric with the CI[1] channel index. This randomization process is carried out in the same manner as the single preselected antenna embodiments detailed with reference to FIGS. 3A, 3B and 4. However, in the present embodiments, the randomization process is utilized when there is more than one channel having the same minimum overall channel metric (based upon channel metrics for each antenna) for each available channel instead of performing the randomization process when more than one available channel have the same minimum single channel metric (based upon a single preselected antenna) as described in FIGS. 3A, 3B and 4.
  • the process of selecting an available channel is carried out in the same manner as the embodiments detailed with reference to FIGS. 3 A, 3B and 4.
  • the overall channel metric (based upon channel metrics for each antenna) for each available channel is utilized in the DCS algorithm to select an available channel instead of a single channel metric from a preselected antenna for each available channel as described in FIGS. 3A, 3B and 4.
  • the DCS module 742 determines whether the overall channel metric of an available channel having the lowest overall channel metric of the available channels, i.e.,
  • CM [1] is greater than an upper threshold (STEP 810 of FIG. 8).
  • Step 810 of FIG. 8 is not performed or the threshold is ignored and the DCS module 742 continues to analyze the available channels without comparing it to a threshold.
  • a retry counter r is defined and set to zero when the DCS algorithm initiates. After determining overall channel metrics for each available channel, if the minimum overall channel metric, i.e., CM [1], is above an upper threshold and the retry counter is less than R , the DCS process is restarted again, i.e., the available channels will be probed again (Step 802 of FIG. 8).
  • Step 810 of FIG. 8 a determination is made as to whether co-channel signaling (also generically referred to as other signaling) is present on CI[1] .
  • Co-channel signaling refers to other communications received on the available channel CI[1], not generated by the receiver 700 and the terminals it is intended to communicate with. These other signals may be any other communication burst from another transmitter in the vicinity.
  • the co-channel signaling is signaling that is highly correlated with signaling of the present system.
  • the co-channel signaling represent a co-channel interference that typically cannot be removed in the baseband processing as opposed to adjacent channel interference.
  • a determination is made as to whether co-channel signaling is present on the available channel having the lowest overall channel metric (i.e. CI[1]) of the available channels. (Step 812 of FIG.
  • preamble detectors 736, 740 provide an indication, e.g., a signal, to the DCS module 742 when a PHY preamble (or other co-channel signal) is detected on available channel CI[1].
  • a PHY preamble or other co-channel signal
  • two received signaling samples from two particular antennas are provided through the antenna selector 716 and through the tuner 718 to the RF/IF downconverters 722, 724. The two received signaling samples are then converted to two intermediate frequency signaling samples by the RF/IF downconverters 722, 724.
  • the baseband downconverter portions 726, 728 are each coupled to a respective IF output of the RF/IF downconverters 722, 724.
  • the baseband downconverter portions 726, 728 each convert one of the two intermediate frequency signaling samples from respective RF/IF downconverters 722, 724 to baseband.
  • the baseband downconverter portions 726, 728 then each provide a baseband signal to a respective A/D converter 756, 758.
  • the A/D converters each digitize the respective baseband signals and provide respective digitized baseband signals to the preamble detectors 736, 738.
  • each of the preamble detectors 736, 740 determines whether a preamble or other interfering co- channel signal is present in the signaling. If a preamble is not detected, the available channel having the lowest overall channel metric is chosen for communications since the detected signal is non-interfering. If there is no co-channel signaling present on the available channel having the lowest overall channel metric (Step 814 of FIG. 8), then the available channel having the lowest overall channel metric is selected for communications (Step 816 of FIG. 8).
  • Step 814 of FIG. 8 If co-channel signaling is detected on the available channel having the lowest overall channel metric (e.g., a PHY preamble is detected on CI[1]), then a comparison of the overall channel metric of the available channel having the lowest overall channel metric with an overall channel metric of a available channel having a higher overall channel metric is made (Step 818 of FIG. 8).
  • CI[1] is compared with other available channels starting from available channel CI[2]. In these embodiments, if all the other available channels have overall channel metrics that are greater than the overall channel metric of CI[1] by- more than a prescribed threshold (Step 820 of FIG. 8)(e.g., 10-15dB), then CI[1] is selected as an available channel for communications (Step 822 of FIG. 8).
  • a prescribed threshold e.g., 10-15dB
  • the DCS algorithm determines whether co-channel signaling is present on the available channel having a higher overall channel metric (Step 824 of FIG. 8) than CI[1].
  • the determination of whether co-channel signaling is present on an available channel having a higher overall channel metric than CI[1] involves the DCS algorithm determining, beginning with available channel CI[2] and proceeding in order to the other available channels, whether co-channel signaling is present on each of the available channels having an overall channel metric greater than CM[1]. Once a particular available channel is found that does not have co-channel signaling present on it (and the particular available channel has signal activity that is no stronger than the signal activity of CI[1] by no more than the prescribed threshold) that particular available channel is selected for communications. As described above, the co-channel signaling is interfering signaling that is highly correlated with signaling of the present system.
  • the determination as to whether co-channel signaling is present on other available channels having a higher overall channel metric than CI[1] comprises a determination as to whether a PHY preamble is present on the available channels having higher overall channel metrics. In one embodiment, this determination is made in the same way the determination is made as to whether a preamble is present on channel CI[1] as discussed above.
  • the DCS module 742 receives a signal from the preamble detectors 736, 740 of FIG. 7 A when there is a PHY preamble present on the available channels having higher overall channel metrics (i.e. the DCS module obtains an indication whether co-channel signaling is present on an available channel having a higher overall channel metric than CI[1].)
  • the DCS algorithm selects the available channel with minimum interference, i.e., channel CI[1], regardless of any co-channel signaling present on CI[1]. Thus, the DCS algorithm selects a channel for communications based upon whether the co-channel signaling is detected on the available channel having the higher overall channel metric (Step 826 of FIG. 8)(i.e., a higher overall channel metric than CI[1]).
  • the DCS algorithm selects an available channel for communications based upon one or more of the following criteria: (a) whether the co-channel signaling is present on the available channel having the lowest overall channel metric; (b) the difference between the available channel having the lowest overall channel metric and the available channel having a higher overall channel metric; and (c) whether the co-channel signaling is detected on the available channel having a higher overall channel metric.
  • the DCS algorithm for multiple receive antennas is applied both to provide an Initial DCS (IDCS) at the time during which the AP is powered-up, and to provide Ongoing DCS (ODCS) during the AP operation.
  • IDCS Initial DCS
  • ODCS Ongoing DCS
  • all terminals stop communicating so that received signal strength measurements may again be taken, and the same process for selecting one of the available channels is carried out as discussed above.
  • the reasons for the ODCS process to engage may be high error rates, a large number of cyclic redundancy check (CRC) errors, or retransmissions.
  • CRC cyclic redundancy check
  • One or a collection of these parameters may be used at the AP to decide whether the AP should enter the DCS mode again to find a better available channel to avoid further deterioration of the system throughput in the immediate future.
  • the DCS operation will be entirely handled by the AP, and no assistance will be provided by the RTs for the ODCS process.
  • provisions in the media access control (MAC) design may be made to facilitate the participation of RTs in the ODCS process to assist the AP in finding the best available channel to move to.
  • the AP delegates to the RT the process of making measurements on other available channels. The RT then sends a report back to the AP at the end of the measurement process.
  • RT Assisted DCS RADCS
  • steps of the DCS algorithm need not be carried out solely by elements of the AP and may be performed by other components of the communication system.
  • Steps 808 though 826 may be performed as described in Steps 406-424 of FIG. 4 above, however, the channel metric of FIG. 4 is replaced with the overall channel metric in FIG. 8.
  • FIG. 7B shown is a functional block diagram of several components of another embodiment of the receiver of FIG. 7A which according to several embodiments of the invention, implements the dynamic channel selection algorithm for selecting one of many available channels for communications with other communication terminals.
  • a receiver 750 including the antennas 702, 704, 706, 708, 710, 712, a radio frequency to baseband frequency integrated circuit'' device 762 (hereinafter referred to as the RF/BB IC device 762) that comprises the antenna selector 716; the tuner 718; radio frequency to baseband frequency downconverters 752, 754 (hereinafter referred to as RF/BB downconverters 752, 754); the analog to digital (A/D) converters 756, 758; the multiplexer 760; the auxiliary analog to digital (A/D) converter 762; and the Analog Received Signal Strength Indication (ARSSI) portions 730, 731 (also referred to as the received signal strength modules 730, 731).
  • the RF/BB IC device 762 radio frequency to baseband frequency integrated circuit'' device 762
  • the baseband integrated circuit device 732 also referred to as the baseband IC device 732 that comprises the demodulators 734, 738; the preamble detectors 736, 740 (also referred to generically as the "co-channel signal detectors”); and the dynamic frequency selection module 742 (also referred to as the DCS module 742). Additionally shown is the channel select signal 744 that couples the DCS module 742 and the tuner 718 and an antenna select signal 746 that couples the DCS module 742 and the antenna selector 716.
  • the receiver 750 in several embodiments, operates in much the same way as the receiver 700; however, the signals from the tuner 718 are received by the RF/BB downconverters 752, 754 and converted directly to a baseband frequency instead of being converted to an intermediate frequency.
  • the RF/BB downconverters 752, 754 provide their respective signals at baseband frequency to the respective received signal strength modules 730, 731 where received signal strength measurements are taken of the signals at baseband frequency instead of at an intermediate frequency.
  • receiver 750 may be referred to as a zero IF receiver.
  • the baseband signals from the RF/BB downconverters 752, 754 are provided directly to the A/D converters 756, 758.
  • baseband signals from the RF/BB downconverters 752, 754 are provided to the respective A/D converters 756, 758 where the baseband signals are digitized.
  • the digitized baseband signals from the A/D converters 756, 758 are then provided to the respective preamble detectors 736, 740 where the determination as to whether co-channel signaling is present on a particular channel is made in accordance with the steps set forth in FIG. 4.
  • receivers 700, 750 of FIG. 7A and FIG. 7B may be implemented as a set of instructions that are performed in dedicated hardware, firmware or in software using a processor or other machine to execute the instructions to accomplish the provided functionality.
  • the receivers 700, 750 of FIG. 7A and FIG. 7B may be implemented as one or more integrated circuit (IC) devices.
  • IC integrated circuit
  • the antennas 702, 704, 706, 708, 710, 712, the antenna selector 716, the tuner 718, the RF/IF downconverters 722, 724, the IF to baseband downconverters 726, 728, the analog to digital (A/D) converters 756, 758, the multiplexer 760; the auxiliary analog to digital (A/D) converter 762, and the received signal strength modules 730, 731 are implemented on the RF/IF IC device 714, while the remaining functional components of the receiver, including the DCS module 742 are implemented on the baseband IC device 732, which is coupled to the RF/IF IC device 714.
  • the antennas 702, 704, 706, 708, 710, 712, the antenna selector 716, the tuner 718, the RF/BB downconverters 752, 754, the analog to digital (A/D) converters 756, 758, the multiplexer 760; the auxiliary analog to digital (A/D) converter 762, and the received signal strength modules 730, 731 are implemented on the RF/BB IC device 762, while the remaining functional components of the receiver, including the DCS module 742 are implemented on the baseband IC device 732, which is coupled to the RF/BB IC device 762.
  • integrated circuit devices 714, 762 and 732 may be referred to application specific integrated circuits (ASICs) or generically as chips.
  • ASICs application specific integrated circuits
  • the RF/IF IC device 714, the RF/BB IC device 762 and the baseband IC device 732 may be implemented as a single chip or ASIC.
  • the RF/IF IC device 714, the RF/BB IC device 762 and the baseband IC device 732 may be a part of a chipset or a single chip or ASIC designed to implement the function blocks of the receivers 700, 750.
  • the steps of FIG. 8 may be performed as a set of instructions that are performed in dedicated hardware, firmware or in software using a processor or other machine to execute the instructions to accomplish the given steps.
  • FIG. 9 shown is a flowchart illustrating the steps performed by the access point of FIG. 7A or FIG. 7B in implementing the DCS algorithm in accordance with one embodiment of the present invention.
  • Q receive antennas e.g., six receive antennas
  • the receiver 700 e.g., antennas 702 through 712 of FIG.
  • n (where n ⁇ 1) receiver chains (e.g., two receiver chains including receiver chain #1 and receiver chain # 2 as described with reference to FIG. 7); thus allowing n antennas to be selected (e.g., by the antenna selector 716) and sampled at the same time (e.g., by the received signal strength modules 730, 731).
  • the Dynamic Channel Selection (DCS) mechanism is employed to avoid occupied frequency channels at the power-up and to ensure a uniform spreading of 5 GHz devices over all the available channels.
  • Ongoing DCS ensures that the best operating channel is used with the minimum level of interference during the entire operation of the AP.
  • DCS operation initially avoids occupied frequency channels that have a high level of interference at the power-up, and Ongoing DCS minimizes the interference in the system by moving to the appropriate available channel during the operation of the system. Such operation will support high density deployments for the 5 GHz wireless devices.
  • the DCS algorithm operates to calculate channel metrics for each antenna over a particular available channel in much the same way as the DCS algorithm in the embodiments described with reference to FIG. 5 calculate channel metrics for each available channel.
  • an overall channel metric (based upon channel metrics for each antenna) for each available channel is utilized in the DCS algorithm to select an available channel instead of a single channel metric from a single antenna for each available channel as described in FIG. 5.
  • the DCS algorithm upon power-up, the DCS algorithm is started (Step 902), and an available channel index i is set to 1 (Step 904). If the channel index i is not greater than eight (Step 905), an available channel is selected by tuning (e.g., with the tuner 718 of FIG.
  • the received signal strength measurements taken over each antenna may be either utilized (e.g., by the DCS module 742 of FIG. 7) as discrete received signal strength measurements or received signal strength measurements that are an average of a small number (e.g., four) of the discrete received signal strength measurements.
  • a channel metric for the first antenna and the second antenna over the first available channel is determined by averaging these M largest measurements using equation (5) (Step 914).
  • Step 916 After channel metrics are determined for the first and second antennas over the first available channel, the antenna selector pointer a is incremented by 1 (Step 916), and Steps 909 tlirough 916 are repeated until a is greater than 2 (Step 909) at which point channel metrics for all the Q antennas will have been determined over the first available channel. It is noted that other methods may be used to determine the channel metrics for each of Q antennas taken ⁇ at a time as described herein. Thus, Steps 909 though 916 represent one embodiment of accomplishing steps 802 and 804 of FIG. 8. After channel metrics for all the antennas are established over the first available channel, an overall channel metric is assigned to the first available channel using Equation (6) (Step 918). Thus, an overall channel metric equal to the maximum of the channel metrics of the antennas (for the first available channel) is established for the first available channel.
  • Step 920 the available channel index i is incremented by one (Step 920), and Steps 905 through 920 are repeated until until i > I (e.g., until i > 8) (Step 905) so that each of the eight available channels is assigned an overall channel metric. It is noted that other methods may be used to determine the overall channel metric for each available channel as described herein. Thus, Step 918 is one embodiment of accomplishing Step 806 of FIG. 8.
  • the DCS algorithm After gathering the overall channel metrics for all the eight available channels (in the 5150-5350 MHz band), the DCS algorithm proceeds by sorting the available channels by their overall channel metrics in ascending order (Step 922).
  • the DCS algorithm compares the CM [1] element, which is the available channel with the minimum overall channel metric (which is also referred to as the QUIETEST channel, among all the eight channels) against an upper threshold (UT) (Step 924). If the signal activity in the QUIETEST channel is above the upper threshold, essentially that means none of the available channels is really "interference free enough" to be selected, and in one embodiment, a retry counter r (that is set to zero upon initiation of the DCS algorithm) is incremented by one (Step 926).
  • a retry counter r that is set to zero upon initiation of the DCS algorithm
  • Step 927 If the retry counter is less than a predetermined maximum number of attempts R (Step 927), the DCS process is restarted again (Step 902), i.e., the available channels will be probed again.
  • the Steps of 902 though 927 will be repeated up to R times, and if this event happens again (i.e. the QUIETEST channel has an overall channel metric greater than an upper threshold (Step 924 and 927)), the available channel with the minimum overall channel metric will be selected (Step 928).
  • CM [1] is not greater than the upper threshold (UT) (Step 924)
  • a determination is made as to whether a PFTY preamble i.e., one example of an interfering co-channel signal
  • available channel CI[1] Step 930
  • a preamble it means that, probably this is not a co-channel signal (but there might be a non 802.11a device in the same band), and available channel CI[1] is selected (Step 928).
  • Step 930 If a PHY preamble is detected on the first available channel CI[1] (Step 930), then the DCS algorithm starts searching for an available channel having a higher overall channel metric with an acceptable level of interference that does not have a preamble detected on it (Step 932).
  • the first step in the search for such an available channel is to compare available channel CI[1] with the other available channels st-arting from available channel CI[2] by subtracting CM [1] from CM [2] (Step 934).
  • the next test is to check whether signal activity in available channel CI[2] is stronger than signal activity in available channel CI[1] by more than a threshold of approximately 10 dB (Step 936). If CM [2] - CM [1]>10 dB (Step 936) available channel CI[1] is selected (Step 928).
  • CM [2] is not greater than CM [1] by more than about 10 dB (Step 936)
  • Step 945 This continuing search involves repeating Steps 934 through 945 as necessary while the channel index i less than eight (Step 945). If all available channels are exhausted and still no available channel is selected (i.e., the channel index i is greater than or equal to eight (Step 945)), the DCS algorithm selects the available channel with minimum interference, available channel CI[1] (Step 928). Once an available channel is selected, the DCS algorithm continues to monitor the communications taking place for a DCS triggering event as part of an Ongoing DCS (ODCS) operation (Step 946). Potential DCS triggering events include high error rates, a large number of CRC errors, or retransmissions. One or a collection of these parameters may be used at the AP to trigger the start of the DCS algorithm again (Step 902) to find a better available channel to avoid further deterioration of the system throughput in the immediate future.
  • ODCS Ongoing DCS
  • the steps of the DCS algorithm shown with reference to FIG. 9 in several embodiments are handled by the AP, without assistance from the RTs.
  • provisions may be made in MAC design to facilitate the participation of RTs in the ODCS process to assist the AP in finding the best available channel to move to.
  • the AP will give delegation to the RT to go and make measurements on other available channels and send a report back to the AP at the end of the measurement process. During this time, the AP will not schedule any traffic to this delegated RT.
  • Such a process may be referred to as RT Assisted DCS (RADCS).
  • steps listed in FIG. 9 generally represent the steps in performing the DCS algorithm according to several embodiments of the invention. These steps may be performed by the DCS module 742 of FIG. 7 A or FIG. 7B and/ or may be performed as a set of instructions that are performed in dedicated hardware, firmware or in software using a processor or other machine to execute the instructions to accomplish the given steps.
  • Steps 904, 905, 906, and 910 are varied depending on the type of channel being selected.

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Abstract

La présente invention concerne un modem sans fil (300) présentant un module RF/FI (304) et un module bande de base (312).
PCT/US2003/007450 2002-03-19 2003-03-11 Selection de canal dynamique dans des modems sans fil WO2003081925A1 (fr)

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