Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/20—Monitoring; Testing of receivers
  • H04B17/24—Monitoring; Testing of receivers with feedback of measurements to the transmitter
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/30—Monitoring; Testing of propagation channels
  • H04B17/309—Measuring or estimating channel quality parameters
  • H04B17/345—Interference values
• • 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

Definitions

• the present invention relates to wireless communications system and, more particularly, to method and apparatus for collecting, measuring, reporting and/or using information which can be used for interference control purposes in a wireless communications system.
• wireless terminals contend for system resources in order to communicate with a common receiver over an uplink channel.
• An example of this situation is the uplink channel in a cellular wireless system, in which wireless terminals transmit to a base station receiver.
• a wireless terminal transmits on the uplink channel it typically causes interference to the entire system, e.g., neighboring base station receivers. Since wireless terminals are distributed, controlling the interference generated by their transmission is a challenging problem.
• Many cellular wireless systems adopt simple strategies to control uplink interference. For example CDMA voice systems (e.g., IS-95) simply power control wireless terminals in such a manner that their signals are received at the base station receiver at approximately the same power.
• CDMA voice systems e.g., IS-95
• CDMA systems such as IxRTT and IxEV-DO allow for wireless terminals to transmit at different rates, and be received at the base station at different powers.
• interference is controlled in a distributed manner which lowers the overall level of interference without precisely controlling those wireless terminals that are the worst sources of interference in the system.
• a base station could be provided with information that could be used in determining the amount of signal interference that will be created in neighboring cells when a transmission occurs and/or the amount of interference a wireless terminal is likely to encounter due to signal interference. It would be particularly desirable if information which can be used for interference determination purposes could be supplied by one or more wireless terminals to a base station.
• Figure 1 is a drawing of an exemplary wireless communications system implemented in accordance with the present invention.
• Figure 2 shows an example of a base station implemented in accordance with the present invention.
• Figure 3 illustrates a wireless terminal implemented in accordance with the present invention.
• Figure 4 illustrates a system in which a wireless terminal is connected to a base station sector and measures the relative gains associated with a plurality of interfering base stations in accordance with the invention.
• Figure 5 is a flow chart illustrating a method of measuring signal energy, determining gains and providing interference reports in accordance with the invention.
• Figure 6 illustrates an uplink traffic channel and segments included therein
• Figure 7 illustrates assignments which can be used by a base station to assign uplink traffic channel segments to a wireless terminal.
• the present invention is directed to methods and apparatus for collecting, measuring, reporting and/or using information which can be used for interference control purposes.
• wireless terminals measure signals transmitted from one or more base stations, e.g., base station sector transmitters.
• the measured signals may be, e.g., beacon signals and/or pilot signals.
• the beacon signals may be narrowband signals, e.g., a single tone.
• the beacon signals may have a duration of one, two or more symbol transmission time periods.
• other types of beacon signals may be used and the particular type of beacon signal is not critical to the invention.
• the wireless terminal From the measured signals, the wireless terminal generates one or more gain ratios which provide information about the relative gain of the communications channels from different base station sectors to the wireless terminal. This information represents interference information since it provides information about the signal interference that will be caused by transmissions to other base station sectors relative to transmissions made to the base station sector to which the wireless terminal is attached.
• reports are generated in accordance with the invention and sent to one or more base stations.
• the reports may be in a plurality of different formats and may provide information about the interference from one interfering base station or the interference caused by multiple interfering base stations.
• One format provides information about the interference which is caused be a single interfering base station sector transmitter relative to a base station sector to which the wireless terminal is connected.
• a base station may request from a wireless terminal a transmission of an interference report providing interference about a specific base station sector. This is done by the base station transmitting a request for a specific interference report to the wireless terminal.
• the request normally identifies the interfering BS sector for which the report is sought.
• the wireless terminal will respond to such a request by transmitting the requested report.
• wireless terminals In addition to responding to requests for specific interference reports, wireless terminals, in some embodiments, transmit interference reports generated in accordance with the invention according to a reporting schedule. In such embodiments, a base station having an active connection with a wireless terminal will receive interference reports on a predictable, e.g., predetermined, schedule.
• generation of gain ratios and/or reports may be a function of various factors indicative of relative transmission power levels used by different base station sectors and/or for different signals which may be measured. In this manner, signals which are transmitted at different power levels, e.g., pilots and beacon signals, can be measured and used in generating reliable relative channel gain estimates by taking into consideration the different relative transmission power levels of the various signals being measured.
• the air link resource generally includes bandwidth, time or code.
• the air link resource that transports user data and/or voice traffic is called the traffic channel.
• Data is communicated over the traffic channel in traffic channel segments (traffic segments for short). Traffic segments may serve as the basic or minimum units of the available traffic channel resources.
• Downlink traffic segments transport data traffic from the base station to the wireless terminals
• uplink traffic segments transport data traffic from the wireless terminals to the base station.
• One exemplary system in which the present invention may be used is the spread spectrum OFDM (orthogonal frequency division multiplexing) multiple-access system in which, a traffic segment includes a number of frequency tones defined over a finite time interval.
• FIG. 1 is an illustration of an exemplary wireless communications system 100, implemented in accordance with the present invention.
• Exemplary wireless communications system 100 includes a plurality of base stations (BSs): base station 1 102, base station M 114.
• Cell 1 104 is the wireless coverage area for base station 1 102.
• BS 1 102 communicates with a plurality of wireless terminals (WTs): WT(I) 106, WT(N) 108 located within cell 1 104.
• WT(I) 106, WT(N) 108 are coupled to BS 1 102 via wireless links 110, 112, respectively.
• Cell M 116 is the wireless coverage area for base station M 114.
• BS M 114 communicates with a plurality of wireless terminals (WTs): WT(I ') 118, WT(N') 120 located within cell M 116.
• WT(I ') 118, WT(N') 120 are coupled to BS M 114 via wireless links 122, 124, respectively.
• WTs (106, 108, 118, 120) may be mobile and/or stationary wireless communication devices.
• Mobile WTs sometimes referred to as mobile nodes (MNs)
• MNs mobile nodes
• Region 134 is a boundary region between cell 1 104 and cell M 116. In the Fig. 1 system, the cells are shown as single sector cells. Multi-sectors cells are also possible and are supported.
• the transmitter of a base station sector can be identified based on transmitted information, e.g., beacon signals, which communicate a base station identifier and/or sector identifier.
• Network node 126 is coupled to BS 1 102 and BS M 114 via network links 128, 130, respectively.
• Network node 126 is also coupled to other network nodes / Internet via network link 132.
• Network links 128, 130, 132 may be, e.g., fiber optic links.
• Network node 126 e.g., a router node, provides connectivity for WTs, e.g., WT(I) 106 to other nodes, e.g., other base stations, AAA server nodes, Home agents nodes, communication peers, e.g., WT(N'), 120, etc., located outside its currently located cell, e.g., cell 1 104.
• FIG. 2 illustrates an exemplary base station 200, implemented in accordance with the present invention.
• Exemplary BS 200 may be a more detailed representation of any of the BSs, BS 1 102, BS M 114 of Figure 1.
• BS 200 includes a receiver 202, a transmitter 204, a processor, e.g., CPU, 206, an I/O interface 208, I/O devices 210, and a memory 212 coupled together via a bus 214 over which the various elements may interchange data and information.
• the base station 200 includes a receiver antenna 216 which is coupled to the receiver 202 and a transmitter antenna 218 which is coupled to transmitter 204.
• Transmitter antenna 218 is used for transmitting information, e.g., downlink traffic channel signals, beacon signals, pilot signals, assignment signals, interference report request messages, interference control indicator signals, etc., from BS 200 to WTs 300 (see Figure 3) while receiver antenna 216 is used for receiving information, e.g., uplink traffic channel signals, WT requests for resources, WT interference reports, etc., from WTs 300.
• the memory 212 includes routines 220 and data/information 224.
• the processor 206 executes the routines 220 and uses the data/information 224 stored in memory 212 to control the overall operation of the base station 200 and implement the methods of the present invention.
• I/O devices 210 e.g., displays, printers, keyboards, etc., display system information to a base station administrator and receive control and/or management input from the administrator.
• I/O interface 208 couples the base station 200 to a computer network, other network nodes, other base stations 200, and/or the Internet.
• base stations 200 may exchange customer information and other data as well as synchronize the transmission of signals to WTs 300 if desired.
• I/O interface 208 provides a high speed connection to the Internet allowing WT 300 users to receive and/or transmit information over the Internet via the base station 300.
• Receiver 202 processes signals received via receiver antenna 216 and extracts from the received signals the information content included therein.
• the extracted information e.g., data and channel interference report information
• the extracted information is communicated to the processor 206 and stored in memory 212 via bus 214.
• Transmitter 204 transmits information, e.g., data, beacon signals, pilot signals, assignment signals, interference report request messages, interference control indicator signals, to WTs 300 via antenna 218.
• Routines 220 include communications routines 226, and base station control routines 228.
• the base station control routines 228 include a scheduler 230, a downlink broadcast signaling module 232, a WT report processing module 234, a report request module 236, and an interference indicator module 238.
• the report request module 236 can generate requests for specific interference reports concerning a particular BS sector identified in the report request. Generated report requests are transmitted to one or more wireless terminals when the BS seeks interference information at a time other than that provided for by a predetermined or fixed reporting schedule.
• Data/Information 224 includes downlink broadcast reference signal information 240, wireless terminal data/information 241, uplink traffic channel information 246, interference report request information messages 248, and interference control indicator signals 250.
• Downlink broadcast reference signal information 240 includes beacon signal information 252, pilot signal information 254, and assignment signal information 256.
• Beacon signals are relatively high power OFDM broadcast signals in which the transmitter power is concentrated on one or a few tones for a short duration, e.g., one symbol time.
• Beacon signal information 252 includes identification information 258 and power level information 260.
• Beacon identification information 258 may include information used to identify and associate the beacon signal with specific BS 200, e.g., a specific tone or set of tones which comprise the beacon signal at a specific time in a repetitive downlink transmission interval or cycle.
• Beacon power level information 260 includes information defining the power level at which the beacon signal is transmitted.
• Pilot signals may include known signals broadcast to WTs at moderately high power levels, e.g., above ordinary signaling levels, which are typically used for identifying a base station, synchronizing with a base station, and obtaining a channel estimate.
• Pilot signal information 254 includes identification information 262 and power level information 264.
• Pilot identification information 262 includes information used to identify and associate the pilot signals with specific base station 200.
• Pilot power level information 264 includes information defining the power level at which the pilot signals are transmitted.
• Various signals providing information about signal transmission power levels e.g., pilot and beacon signal transmission pilot levels, may be broadcast for use by wireless terminals in determining gain ratios and/or interference reports.
• Assignment signals includes broadcast uplink and downlink traffic channel segment assignment signals transmitted typically at power levels above ordinary signaling levels so as to reach WTs within its cell which have poor channel quality conditions.
• Assignment signaling information 256 includes identification information 266 and power level information 268.
• Assignment signaling identification information 266 includes information associating specific tones at specific times in the downlink timing cycle with assignments for the specific BS 200.
• Assignment power level information 268 includes information defining the power level at which the assignment signals are transmitted.
• Wireless terminal data/information 241 includes a plurality of sets of WT data/information, WT 1 information 242, WT N info 244.
• WT 1 information 242 includes data 270, terminal identification information 272, interference cost report information 274, requested uplink traffic segments 276, and assigned uplink traffic segments 278.
• Data 270 includes user data associated with WT 1, e.g., data and information received from WTl intended to be communicated by BS 200 either directly or indirectly to a peer node of WTl, e.g., WT N, in which WT 1 is participating in a communications session.
• Data 270 also includes received data and information originally sourced from a peer node of WT 1, e.g., WT N.
• Terminal identification information 272 includes a BS assigned identifier associating WT 1 to the BS and used by the BS to identify WT 1.
• Interference cost report information 274 includes information which has been forwarded in a feedback report from WT 1 to BS 200 identifying interference costs of WT 1 transmitting uplink signaling to the communications system.
• Requested uplink traffic segments 276 include requests from WTl for uplink traffic segments which are allocated by the BS scheduler 230, e.g., number, type, and/or time constraint information.
• Assigned uplink traffic segments 278 includes information identifying the uplink traffic segments which have been assigned by the scheduler 230 to WT 1.
• Uplink traffic channel information 246 includes a plurality of uplink traffic channel segment information sets including information on the segments that may be assigned by BS scheduler 230 to WTs requesting uplink air link resources.
• Uplink traffic channel information 246 includes channel segment 1 information 280 and channel segment N information 282.
• Channel segment 1 information 280 includes type information 284, power level information 286, definition information 288, and assignment information 290.
• Type information 284 includes information defining the characteristics of the segment 1, e.g., the frequency and time extent of the segment.
• the BS may support multiple types of uplink segments, e.g., a segment with a large bandwidth but a short time durations and a segment with a small bandwidth but a long time duration.
• Power level information 286 includes information defining the specified power level at which the WT is to transmit when using uplink segment 1.
• Definition information 288 includes information defining specific frequencies or tones and specific times which constitute uplink traffic channel segment 1.
• Assignment information 290 includes assignment information associated with uplink traffic segment 1, e.g., the identifier of the WT being assigned the uplink traffic channel segment 1, a coding and/or a modulation scheme to be used in uplink traffic channel segment 1.
• Interference report request information messages 248, used in some embodiments, are messages to be transmitted, e.g., as a broadcast messages or as messages directed to specific WTs.
• the by BS 200 may transmit to WTs 300 on a common control channel instructing the WTs to determine and report the interference information with respect to a particular base station transmitter, e.g., base station sector transmitter, in the communications system.
• Interference report request information messages 248 normally include base station transmitter identification information 292 which identifies the particular base station sector being currently designated for the interference report. As discussed above, some base stations are implemented as single sector base stations. Over time BS 200 may change base station identification information 292 to correspond to each of the neighboring transmitters and thereby obtain interference information about multiple neighbors.
• Interference control indicator signals 250 used in some embodiments, e.g., where at least some of the uplink traffic segments are not explicitly assigned by the base station, are signals broadcast by BS 200 to WTs 300 to control, in terms of interference, which WTs may use uplink traffic segments. For example, a multi-level variable may be used where each level indicates how tightly the BS 200 would like to control interference. WTs 300 which receive this signal can use this signal in combination with their own measured interference to determine whether or not the WT 300 is allowed to use the uplink traffic segments being controlled.
• Communication routines 226 implement the various communications protocols used by the BS 200 and control overall transmission of user data.
• Base station control routines 228 control the operation of the I/O devices 210, I/O interface 208, receiver 202, transmitter 204, and controls the operation of the BS 200 to implement the methods of the present invention.
• Scheduler 230 allocates uplink traffic segments under its control to WTs 300 based upon a number of constraints: power requirement of the segment, transmit power capacity of the WT, and interference cost to the system. Thus, the scheduler 230 may, and often does, use information from received interference reports when scheduling downlink transmissions.
• Downlink broadcast signaling module 232 uses the data/information 224 including the downlink broadcast reference signal information 240 to generate and transmit broadcast signals such as beacons, pilot signals, assignments signals, and/or other common control signal transmitted at known power levels which may be used by WTs 300 in determining downlink channel quality and uplink interference levels.
• WT interference report processing module 234 uses the data/information 224 including the interference cost report information 274 obtained from the WTs 300 to process, correlate, and forward uplink interference information to the scheduler 230.
• the report request module 236, used in some embodiments, generates a sequence of interference report request messages 248 to request a sequence of uplink interference reports, each report corresponding to one of its adjacent base stations.
• Figure 3 illustrates an exemplary wireless terminal 300, implemented in accordance with the present invention.
• Exemplary wireless terminal 300 may be a more detailed representation of any of the WTs 106, 108, 118, 120 of exemplary system wireless communication system 100 of Figure 1.
• WT 300 includes a receiver 302, a transmitter 304, I/O devices 310, a processor, e.g., a CPU, 306, and a memory 312 coupled together via bus 314 over which the various elements may interchange data and information.
• Receiver 302 is coupled to antenna 316; transmitter 304 is coupled to antenna 316.
• Uplink signals transmitted from BS 200 are received through antenna 316, and processed by receiver 302.
• Transmitter 304 transmits uplink signals through antenna 318 to BS 200.
• Uplink signals includes, e.g., uplink traffic channel signals and interference cost reports.
• I/O devices 310 include user interface devices such as, e.g., microphones, speakers, video cameras, video displays, keyboard, printers, data terminal displays, etc. I/O devices 310 may be used to interface with the operator of WT 300, e.g., to allow the operator to enter user data, voice, and/or video directed to a peer node and allow the operator to view user data, voice, and/or video communicated from a peer node, e.g., another WT 300.
• Memory 312 includes routines 320 and data/information 322.
• Processor 306 executes the routines 320 and uses the data/information 322 in memory 312 to control the basic operation of the WT 300 and to implement the methods of the present invention.
• Routines 320 include communications routine 324 and WT control routines 326.
• WT control routines 326 include a reference signal processing module 332, an interference cost module 334, and a scheduling decision module 330.
• Reference signal processing module 332 includes an identification module 336, a received power measurement module 338, and a channel gain ratio calculation module 340.
• Interference cost module 334 includes a filtering module 342, a determination module 344, and a report generation module 346.
• the report generation module 346 includes a quantization module 348.
• Data/information 322 includes downlink broadcast reference signal information 349, wireless terminal data/information 352, uplink traffic channel information 354, received interference report request information message 356, received interference control indicator signal 358, and received broadcast reference signals 353.
• Downlink broadcast reference signal information 349 includes a plurality of downlink broadcast reference signal information sets, base station 1 downlink broadcast reference signal information 350, base station M downlink broadcast reference signal information 351.
• BS 1 downlink broadcast reference signal information includes beacon signal information 360, pilot signal information 362, and assignment signaling information 364.
• Beacon signal information 360 includes identification information 366, e.g., BS identifier and sector identifier information, and power level information 368.
• Pilot signal information 362 includes identification information 370 and power level information 372.
• Assignment signaling information 364 includes identification information 374 and power level information 376.
• Wireless terminal data/information 352 includes data 382, terminal identification information 384, interference report information 386, requested uplink traffic segments 388, and assigned uplink traffic segments 390.
• Uplink traffic channel information 354 includes a plurality of uplink traffic channel information sets, channel 1 information 391, channel N information 392.
• Channel 1 information 391 includes type information 393, power level information 394, definition information 395, and assignment information 396.
• the scheduling module 330 controls the scheduling of the transmission interference reports, e.g., according to a predetermined schedule, BS requested interference reports in response to received report requests, and user data.
• Received interference report request information message 356 includes a base station identifier 397.
• Fig. 4 illustrates an exemplary system 400 implemented in accordance with the invention which will be used to explain various features of the invention.
• the system 400 includes first, second and third cells 404, 406, 408 which neighbor each other.
• the first cell 404 includes a first base station including a first base station sector transmitter (BSSo) 410 and a wireless terminal 420 which is connected to BSSo 410.
• the second cell 406 includes a station base station including a second base station sector transmitter (BSSi) 412.
• the third cell 408 includes a third station base station including a third base station sector transmitter (BSS 2 ) 414.
• signals transmitted between BSSo and the WT 420 are subjected to a channel gain go.
• a gain ratio G 1 ratio of the channel gain from the BSSi to the WT 420 to the channel gain from the BSS 0 to the WT 420. That is:
• the received power (PB) of the beacon signals received from the base stations BSSo, BSSi, BSS 2 can be used to determine the gain ratio's as follows:
• G 2 g2 /go PB 2 /PBo
• the traffic segments that constitute the uplink traffic channel may be defined over different frequency and time extents in order to suit a broad class of wireless terminals that are operating over a diverse set of wireless channels and with different device constraints.
• Figure 6 is a graph IOOA of frequency on the vertical axis 102A vs time on the horizontal axis 104A.
• Figure 6 illustrates two kinds of traffic segments in the uplink traffic channel. Traffic segment denoted A 106A occupies twice the frequency extent of the traffic segment denoted B 108 A.
• the traffic segments in the uplink traffic channel can be shared dynamically among the wireless terminals that are communicating with the base station.
• a scheduling module that is part of the base station can rapidly assign the traffic channel segments to different users according to their traffic needs, device constraints and channel conditions, which may be time varying in general.
• the uplink traffic channel is thus effectively shared and dynamically allocated among different users on a segment-by-segment basis.
• the dynamic allocation of traffic segments is illustrated in Figure 6 in which segment A is assigned to user #1 by the base station scheduler and segment B is assigned to user #2.
• the assignment information of traffic channel segments is transported in the assignment channel, which includes a series of assignment segments.
• Each traffic segment is associated with a corresponding unique assignment segment that conveys the assignment information that may include the identifier of the wireless terminal and also the coding and modulation scheme to be used in that traffic segment.
• Figure 7 is a graph 200A of frequency on the vertical axis 202A vs. time on the horizontal axis 204A.
• Fig. 7 shows two assignment segments, A' 206A and B' 208 A, which convey the assignment information of the uplink traffic segments A 210A and B 212A, respectively.
• the assignment channel is a shared channel resource.
• the wireless terminals receive the assignment information conveyed in the assignment channel and then transmit on the uplink traffic channel segments according to the assignment information.
• the base station scheduler 230 allocates traffic segments based on a number of considerations.
• One constraint is that the transmit power requirement of the traffic channel should not exceed the transmit power capability of the wireless terminal.
• wireless terminals that are operating over weaker uplink channels may be allocated traffic segments that occupy a narrower frequency extent in the exemplary system in order that the instantaneous power requirements are not severely constraining.
• wireless terminals that generate a greater amount of interference may also be allocated traffic segments that include a smaller frequency extent in order to reduce the impact of the instantaneous interference generated by them.
• the total interference is controlled by scheduling the transmission of the wireless terminals on the basis of their interference costs to the system, which are defined in the following.
• the wireless terminals determine their interference costs to the system from the received downlink broadcast signals.
• the wireless terminals report their interference costs to the base station, in the form of interference reports, which then makes uplink scheduling decisions to control uplink interference.
• the base station broadcasts an interference control indicator, and the wireless terminals compare their interference costs with the received indicator to determine their uplink transmission resources in an appropriate manner, e.g., mobiles have uplink transmission costs below a level indicated by the control indicator may transmit while mobiles with interference costs exceeding the cost level indicated by the control indicator will refrain from transmitting.
• Exemplary Interference costs which may be considered will now be described. [0049] Consider a wireless terminal labeled m 0 .
• the amount of power transmitted by wireless terminal 0 on the uplink traffic segment is usually a function of the condition of the wireless channel from wireless terminal m 0 to the base station B 0 , the frequency extent, and the choice of code rate on the traffic segment.
• the frequency extent of the segment and the choice of code rate determine the transmit power used by the mobile, which is the quantity that directly causes interference.
• P R per tone of the traffic segment which is a function of the choice of code rate and the channel conditions over which the mobile terminal is operating. This is related to the transmit power per tone of the wireless terminal, P ⁇ , as follows:
• G 0,0 wireless terminal m 0 at base station B k is proportional to its transmit power as well as the ratio of the channel gains to base station k and to its own base station.
• ro,k is called the interference cost of wireless terminal m 0 to base station B k .
• ⁇ r Ojl , ... , ⁇ O , N ⁇ are the interference costs of wireless terminal 0 to the entire system. It is useful to note that the aggregate instantaneous interference produced by the mobile m 0 to base station ⁇ is actually given by n tones r 0 k where n tones is the frequency extent of the traffic segment.
• each base station 102, 114 in the exemplary system 100 broadcasts periodic reference signals at high power that the wireless terminals can detect and decode.
• the reference signals include beacons, pilots, or other common control signals.
• the reference signals may have a unique pattern that serves to identify the cell and the sector of the base station.
• a beacon or pilot signal can be used as the reference signals.
• a beacon signal is a special OFDM symbol in which most of the transmission power is concentrated on a small number of tones. The frequency location of those high-power tones indicates the identifier of the base station.
• a pilot signal can have a special hopping pattern, which also uniquely specifies the identifier of the base station 102. Thus, a base station sector can be identified in the exemplary system from beacon and/or pilot signals.
• a pilot signal can be used as the reference signal.
• a pilot is a known spreading sequence with a particular time offset as the identifier of the base station.
• the reference signals are transmitted at known powers. Different reference signals may be transmitted at different powers. Different base stations 102, 114 may use different power levels for the same type of reference signals as long as these powers are known to the mobile terminals.
• the wireless terminal 106 first receives the reference signals to get the identifier of the base station 102. Then, the wireless terminal 106 measures the received power of the reference signals, and calculates the channel gain from the base station 102 to the wireless terminal 106. Note that at a given location, the wireless terminal may be able to receive the reference signals from multiple base stations 102, 114. On the other hand, the wireless terminal may not be able to receive the reference signals from all the base stations in the entire system. In the exemplary system, wireless terminal m 0 monitors Go,o for its connected base station B 0 , and Go, k for base station B k if it can receive the corresponding reference signal. Therefore, wireless terminal m 0 maintains an array of interference costs ⁇ ro,k ⁇ for the set of base stations whose reference signals it can receive
• the wireless terminal 106 can derive the interference costs by combining the estimation from multiple reference signals. For example, in the exemplary OFDM system 100, the wireless terminal 106 may use both beacons and pilots to arrive at the estimation of ⁇ r o , k ⁇ •
• the information of interference costs ⁇ ro,k ⁇ is to be used to control the uplink interference and increase overall system capacity.
• the uplink traffic channels can be used in two modes and the following describes the use of interference costs in both modes.
• the wireless terminals 106, 108 measured the channel gain information from the downlink reference signals, while the interference are a measure of the costs the interference will have in terms of impact on the uplink.
• the channel gains of the downlink and the uplink between a wireless terminal 106 and a base station 102 may not be same at all times.
• the estimates of the channel gains from the downlink reference signals may, and in some embodiments are, averaged (using a form of lowpass filtering for example) to obtain the estimates of interference costs ⁇ r o ,k ⁇ .
• each of the uplink traffic segments are explicitly assigned by the base station so that one uplink traffic segment is only used by at most one wireless terminal.
• each of the uplink traffic segments are explicitly assigned by the base station so that one uplink traffic segment is only used by at most one wireless terminal.
• each wireless terminal 106, 108 sends to the base station 102, which the wireless terminal is connected to, a sequence of interference reports.
• the reports are indicative of the calculated interference costs ⁇ r o , k ⁇ .
• a report is a control message that includes the entire array of interference costs ⁇ ro,k ⁇ •
• a quantized version of the array ⁇ ro,k ⁇ is transmitted. There are a number of ways to quantize ⁇ r o ,k ⁇ , as listed below.
• the base station schedules, e.g., assigns, the traffic segments as a function of the interference information.
• One scheduling policy is to restrict the total interference produced by all scheduled wireless terminals to a pre-determined threshold.
• Another scheduling policy is categorize the wireless terminals according to their reported ⁇ r ⁇ ,k ⁇ to several groups such that the group with large interference costs is preferably assigned traffic segments that include a smaller frequency extent in order to reduce the impact of the instantaneous interference generated.
• each base station 102 is aware of its neighbor set, i.e., the set of base stations 114, etc. that are determined to be neighbors from the perspective of interference.
• the base station 102 just attempts to control the total interference to the neighboring base stations.
• the basic embodiment may be coarse in the sense that almost all the interference may be directed to a particular one of the neighboring base stations (cell X), e.g., because all the scheduled wireless terminals may be close to cell X. In this case, cell X experiences severe interference at this time instant. At another time instant, the interference may be concentrated on a different neighboring base station, in which case cell X experiences little interference.
• the interference to a particular neighboring base station may have large variation.
• the base station 102 may have to leave sufficient margin in the total generated interference to compensate the large variation.
• the base station 102 broadcasts a message on a common control channel instructing the wireless terminals 106, 108 to determine and report the interference cost with respect to a particular base station B k .
• the base station 102 repeats this process for each member of its neighbor set and determines the set of wireless terminals 106, 108 that interfere with each of the base stations.
• the base station 102 can simultaneously allocate uplink traffic segments to a subset of wireless terminals 106, 108 that interfere with different base stations, thereby reducing the variation of the interference directed to any particular base station.
• the base station 102 may allow greater total interference to be generated without severely impacting the system stability, thus increasing the system capacity.
• Wireless terminals 106, 108 in the interior of the cell 104 cause negligible interference to neighboring base stations 114 and therefore may be scheduled at any time.
• each of the uplink traffic segments are not explicitly assigned by the base station 102.
• one uplink traffic segment may be used by multiple wireless terminals 106, 108.
• each wireless terminal 106, 108 makes its own scheduling decision of whether it is to use an uplink traffic segment and if so at what data rate and power.
• the base station broadcasts the interference control indicator.
• Each wireless terminal 106, 108 compares the reference levels with its interference costs and determines its scheduling decision.
• the interference control indicator can be a multi-level variable and each level is to indicate how tightly the base station 102 would like to control the total interference. For example, when the lowest level is broadcasted, then all wireless terminals 106, 108 are allowed to use all the traffic channel segments at all rates. When the highest level is broadcasted, then only the wireless terminals 106, 108 whose interference costs are very low can use the traffic channel segments.
• FIG. 5 is a flowchart 1000 of an exemplary method of operating a wireless terminal, e.g., mobile node, in accordance with the present invention.
• step 1002 Operation starts in step 1002, where the wireless terminal is powered on and initialized. Operation proceeds from step 1002 to step 1004, step 1006 and, via connecting node B 1005 to step 1008. [0072] In step 1004, the wireless terminal is operated to receive beacon and pilot signals from the current base station sector connection. Operation proceeds from step 1004 to step 1010. In step 1010, the wireless terminal measures the power of the received beacon signal (PBo) and received pilot channel signals (PPo) for the current base station sector connection. Operation proceeds from step 1010 to step 1012. In step 1012, the wireless terminal derives current connection base station sector transmitter information, e.g., a BSS slope and a BSS sector type from the received beacon signal.
• PBo received beacon signal
• PPo received pilot channel signals
• Step 1012 includes sub-step 1013.
• the wireless terminal determines a power transmission tier level associated with the current connection base station sector and tone block being used.
• step 1006 the wireless terminal receives beacon signal from one or more interfering base station sectors 1006. Operation proceeds from step 1006 to step 1014.
• Subsequent operations 1014, 1016, 1018 are performed for each interfering base station sector, e.g., interfering base station sector i (BSSi).
• interfering base station sector i BSSi
• step 1014 the wireless terminal measures the power of received beacon signal (PB 1 ) for the interfering base station sector. Operation proceeds from step 1014 to step 1016.
• step 1016 the wireless terminal derives interfering base station sector transmitter information, e.g., a BSS slope and a BSS sector type from the received beacon signal.
• Step 1016 includes sub-step 1017.
• sub-step 1017 the wireless terminal determines a power transmission tier level associated with an interfering base station sector and tone block being used.
• step 1018 the wireless terminal computes a channel gain ratio using the method of sub-step 1020 or the method of sub-step 1022.
• sub-step 1020 the wireless terminal uses beacon signal information to compute the channel gain ratio, G 1 .
• sub-step 1022 the wireless terminal uses beacon signal information and pilot signal information to compute the channel gain ratio G 1 .
• K per tone transmitter power beacon reference level for a tier 0 tone block / per tone transmitter pilot signal reference level for a tier 0 tone block
• Zo power scale factor associated with the power transmission tier level of the tone block for the current base station sector connection transmitter tone block.
• step 1018 proceeds from step 1018 via connecting node A 1042 to step
• step 1008 the wireless terminal is operated to receive broadcast load factor information.
• the wireless terminal receives the load factor information of the current serving base station sector from the broadcast information sent by the current serving base station sector transmitter.
• the wireless terminal may receive the load factor information of the interfering serving base station sector from the broadcast information sent by the current or the interfering serving base station sector transmitter. While load factor information is shown as being received from the current serving base station sector, alternatively, load factor information can be received from other nodes and/or pre-stored in the wireless terminal. For each base station sector under consideration, operation proceeds to step 1028. In step 1028 the wireless terminal determines whether or not the load factor was successfully recovered from the received signal.
• step 1030 the wireless terminal stores the load factor.
• load factor bo the load factor for the current serving base station sector
• load factor b k the load factor for interfering base station section k.
• step 1032 the wireless terminal sets the load factor to 1.
• Load factors (b 0 1032, bi 1034, ..., b k 1038, .. bn 1040) are obtained, with each load factor being sourced from one of steps 1030 and step 1032.
• step 1043 the wireless terminal generates one or more interference reports.
• Step 1043 includes sub-step 1044 and sub-step 1048.
• the wireless terminal In sub- step 1044, the wireless terminal generates a specific type report conveying interference by a specific interfering base station sector to the serving base station sector.
• Step 1044 includes sub-step 1046.
• the wireless terminal generates a generic type report conveying information of interference by one or more interfering BSSs to the serving BSS, e.g., using information from each of the measured beacon signals of interfering base station sectors including using load factor information and power scale factor information.
• step 1043 includes quantization.
• Operation proceeds from step 1043 to step 1050 where the wireless terminal is operated to transmit the report to the current serving base station sector serving as the current attachment point for the wireless terminal.
• the transmission of a report is in response to a request from the serving base station sector.
• the type of report transmitted e.g., specific or generic, is in response to received signaling from a base station sector identifying the type of report.
• the transmission of a particular specific type report reporting on interference associated with a particular base station sector is in response to a received base station signal identifying the particular base station sector.
• interference reports are transmitted periodically in accordance with a reporting schedule being followed by the wireless terminal, e.g., as part of dedicated control channel structure.
• the base station does not signal any report selection information to select the report.
• the system includes a plurality of power transmission tier levels, e.g., three, with a different power scale factor associated with each tier level.
• a power scale factor of 0 dB is associated with a tier level 0 tone block
• a power scale factor of 6 dB is associated with a tier 1 level tone block
• a power scale factor of 12 dB is associated with a tier 2 tone block.
• each attachment point corresponds to a base station sector transmitter and a tone block
• each attachment point BSS transmitter tone block may be associated with a power transmission tier level.
• there are a plurality of downlink tones blocks e.g., three tone block (tone block 0, tone block 1, tone block 2) each having 113 contiguous evenly spaced tones.
• the same tone block e.g., tone block 0, used different base station sector transmitters
• a wireless terminal identifying a particular attachment point, corresponding to a base station sector transmitter and tone block, e.g., from information conveyed via its beacon signal using tone location and/or time position with a recurring transmission pattern, can use stored information to associate the identified attachment point with a particular power transmission tier level and power scale factor for a particular tone block.
• the loading factor e.g., bk
• the loading factor is a value greater than or equal to 0 and less than or equal to one.
• the value is communicated from a base station sector to a wireless terminal represents one of a plurality of levels, e.g., OdB, -IdB, -2dB, -3dB, -4dB, -6dB, -9dB, -infinity dB.
• the beacon signals are transmitted at the same power from a base station sector transmitter irrespective of power transmission tier associated with the tone block being used; however, other downlink signals, e.g., pilot signals, are affected by the power transmission tier associated with the tone block for the base station sector transmitter.
• nodes described herein are implemented using one or more modules to perform the steps corresponding to one or more methods of the present invention, for example, signal processing, beacon generation, beacon detection, beacon measuring, connection comparisons, connection implementations.
• various features of the present invention are implemented using modules. Such modules may be implemented using software, hardware or a combination of software and hardware.
• machine executable instructions such as software
• a machine readable medium such as a memory device, e.g., RAM, floppy disk, etc.
• a machine e.g., general purpose computer with or without additional hardware
• the present invention is directed to a machine- readable medium including machine executable instructions for causing a machine, e.g., processor and associated hardware, to perform one or more of the steps of the above- described method(s).
• the methods and apparatus of the present invention may be, and in various embodiments are, used with CDMA, orthogonal frequency division multiplexing (OFDM), and/or various other types of communications techniques which may be used to provide wireless communications links between access nodes and mobile nodes.
• the access nodes are implemented as base stations which establish communications links with mobile nodes using OFDM and/or CDMA.
• the mobile nodes are implemented as notebook computers, personal data assistants (PDAs), or other portable devices including receiver/transmitter circuits and logic and/or routines, for implementing the methods of the present invention.

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• 2007
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  • 2007-10-09 JP JP2009532541A patent/JP2010507284A/ja active Pending
  • 2007-10-09 WO PCT/US2007/080852 patent/WO2008048827A1/en active Application Filing
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