Patent Document

RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/940,658, filed May 29, 2007 titled “SECTORIZED BASE STATIONS AS MULTIPLE ANTENNA SYSTEMS”, which is assigned to the assignee of the present application and which is hereby expressly incorporated by reference. 
    
    
     FIELD 
     The present invention relates to wireless communications methods and apparatus and, more particularly, to methods and apparatus for improving utilization of air link resources in a wireless communications system including a sectorized base station. 
     BACKGROUND 
     In wireless communications systems sectors are often treated as independent entities. The boundaries between sectors, where receivers receive both sectors at comparable power suffer from the inherent interference. It would be advantageous if methods and apparatus were developed which provided for improved communications in these high interference sector boundary regions. 
     SUMMARY 
     In accordance with various embodiments, the notion of a sector boundary is replaced with that of a MIMO enabled region. In the sector boundary region, mobiles have effective access to two base station sectors, and the system can be treated as a MIMO system. When the mobile has two antennas the setup is inherently 2×2, but it could be X×2, where X is the number of antennas the mobile has and X is an integer greater than 2. Thus, in accordance with various embodiments, a high interference sector boundary region is converted in a high capacity region, e.g., a high capacity MIMO region, by having the sectors coordinated. 
     In some embodiments, a base station operates synchronized sectors, e.g., three synchronized sectors. If in sector boundary regions one takes a MIMO view, one likely discovers a notion of soft sectors. Abstractly, the system behaves like 3 base station antenna MIMO but, a priori, it is known that mobiles typically see only one base station antenna or pairs of base station antennas, e.g., antenna face A, antenna face B, antenna face C or antenna face pair AB, antenna face pair BC, antenna face pair CA—corresponding to six different channel type conditions. A mobile in AB, BC or CA is considered to be in a sector pair state and can be operated to exploit the two sectors as a MIMO system. A mobile that see only a single base station antenna face is considered to be in a sector state and would only have the capabilities supported by that face, e.g. non-MIMO capabilities. Thus the exemplary three sector base station acts more like a big MIMO system with prior knowledge that only the six states are possible, e.g., sector state corresponding to base station antenna face A, sector state corresponding to base station antenna face B, sector state corresponding to base station antenna face C, sector pair state corresponding to antenna face pair AB, sector pair state corresponding to antenna face pair BC, and sector pair state corresponding to antenna face pair CA. Handoff between the six areas is soft and not so critical and typically only between certain pairs. Mobiles that do not have multiple antennas can go into a soft-handoff mode near sector boundaries. 
     In the uplink a mobile can be assigned in both sectors when in the two sector state, sometimes referred to a sector pair state. Two mobiles can be assigned the same air link resource, e.g., the same OFDM tone-symbols, if at least one of them is in the two sector region. MIMO techniques can be used at the base station to process both signals. To support this, the mobiles should be MIMO aware, i.e., aware of the fact that they are participating in a MIMO transmission. 
     The system idea is characterized by the existence of MIMO states across sectors and non-MIMO states for mobiles isolated to one sector. 
     An exemplary method of operating a base station in a sectorized cell will be described in which each sector is adjacent at least one other sector in the cell, adjacent sectors forming sector pairs, said base station being coupled to a multi-face antenna, each face of said antenna corresponding to a different sector of said cell, said sectors being timing synchronized. The exemplary method of operating the base station comprises: for each of a plurality of wireless terminals in said cell, maintaining information indicating whether said wireless terminal is in a sector or sector pair state. The exemplary method of operating the base station further comprises communicating with one of said wireless terminals using a number of antenna faces determined by the state corresponding to said wireless terminal. 
     An exemplary base station in a sectorized cell, each sector being adjacent at least one other sector in the cell, adjacent sectors forming sector pairs, said base station being coupled to a multi-face antenna, each face of said antenna corresponding to a different sector of said cell, said sectors being timing synchronized, will be described. The exemplary base station includes: a wireless terminal state information maintenance module for maintaining information indicating whether a wireless terminal is in a sector or sector pair state for each of a plurality of wireless terminals in said cell; and a communications module for communicating with one of said wireless terminals using a number of antenna faces determined by the state corresponding to said wireless terminal. 
     A method of operating a wireless terminal in accordance with various embodiments includes: maintaining information indicating whether the wireless terminal is in a sector or sector pair state; and communicating with a base station, e.g., a multi-sector base station, in one of a MIMO mode of operation and a non-MIMO mode of operation, the mode of operation used for communicating being a function of whether said maintained information indicates that said wireless terminal is in a sector or sector pair state. In various embodiments communicating with a multi-sector base station in a MIMO mode of operation includes communicating simultaneously with two adjacent base station sector antenna faces using at least some of the same tones, wherein the sectors at the base station are timing synchronized. An exemplary wireless terminal in accordance with various embodiments includes: a state information maintenance module for maintaining information indicating whether said wireless terminal is in a sector or sector pair state; a plurality of antennas; a mode determination module for determining whether said wireless terminal is to operate in a MIMO or non-MIMO mode of operation as a function of said maintained information indicating whether said wireless terminal is in a sector or sector pair state; a MIMO module for communicating with said base station in a MIMO mode of operation; and a non-MIMO mode module for communicating with said base station in a non-MIMO mode of operation. 
     While various embodiments have been discussed in the summary above, it should be appreciated that not necessarily all embodiments include the same features and some of the features described above are not necessary but can be desirable in some embodiments. Numerous additional features, embodiments and benefits are discussed in the detailed description which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a drawing of an exemplary wireless communications system in accordance with various embodiments. 
         FIG. 2  is a drawing of an exemplary base station coupled to a multi-face receive antenna and a multiple face transmit antenna in accordance with various embodiments. 
         FIG. 3  is a drawing of an exemplary wireless terminal, e.g., mobile node, in accordance with various embodiments. 
         FIG. 4  comprising the combination of  FIG. 4A ,  FIG. 4B  and  FIG. 4C  is a flowchart of an exemplary method of operating a base station in accordance with various embodiments. 
         FIG. 5  is a flowchart of an exemplary method of operating a wireless terminal in accordance with various embodiments, including  FIGS. 5A and 5B . 
         FIGS. 6 and 7  illustrate exemplary MIMO signaling in accordance with various embodiments between a wireless terminal with multiple antennas and a base station utilizing a pair of base station adjacent sector antenna faces. 
         FIG. 8  is a drawing illustrating exemplary air link resources corresponding to different sectors of a base station and exemplary tone allocation to wireless terminals in accordance with various embodiments. 
         FIG. 9  is a drawing illustrating sector nulls corresponding to pilot tones in an exemplary OFDM wireless communications system implementing synchronized sectors. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a drawing of an exemplary wireless communications system  100 , e.g., a multiple access orthogonal frequency division multiplexing (OFDM) wireless communications system in accordance with various embodiments. Exemplary wireless system  100  includes a plurality of base stations including multi-sector base station  1   102 . Base station  1   102  is coupled to other network nodes, e.g., other base stations, routers, AAA nodes, home agent nodes, etc., and/or the Internet via network link  101 , e.g., a fiber optic link. Base station  1   102  has a corresponding cellular coverage area represented by cell  1   104  which includes a sector A region  112 , a sector B region  114  and a sector C region  116 . Base station  1   102  is a three sector base station including: a base station sector A module  106  which interfaces with sector A antenna face  118 ; a base station sector B module  108  which interfaces with sector B antenna face  120 ; and a base station sector C module  110  which interfaces with sector C antenna face  122 . Base station  1   102 , has synchronized symbol timing with respect to its sectors. 
     Exemplary wireless communications system  100  also includes a plurality of wireless terminal, e.g. mobile nodes. In this example, exemplary wireless terminals (WT  1   124 , WT  2   126 , WT  3   128 , WT  4   130 , WT  5   132 ) are currently coupled to base station  1   102  and using BS  1   102  as a point of network attachment. WT  1  is currently in a sector state of operation and is communicating with BS  1   102  via antenna face  120  as illustrated by arrow  134 . WT  2  is currently in a sector pair state of operation and is communicating with BS  1   102  via antenna face  118  as illustrated by arrow  136  and via antenna face  122  as indicated by arrow  138 . WT  3  is currently in a sector pair state of operation and is communicating with BS  1   102  via antenna face  118  as illustrated by arrow  140  and via antenna face  122  as indicated by arrow  142 . WT  4  is currently in a sector pair state of operation and is communicating with BS  1   102  via antenna face  120  as illustrated by arrow  144  and via antenna face  122  as indicated by arrow  146 . WT  5  is currently in a sector state of operation and is communicating with BS  1   102  via antenna face  122  as illustrated by arrow  148 . 
     Now consider an example, WT  2  and WT  3  are both in a sector pair state corresponding to same sector pair. BS  1   102  may, and sometimes does, allocate the same tones to be used concurrently in both sector A and sector C by both WT  2  and WT  3  for at least some signaling. WT  4   130  is in a sector pair state and WT  5   132  is in a sector state. BS  1   102  may, and sometimes does, allocate the same tones to be used concurrently in sector C by WT  5   132  and by WT  4   130 . WT  4   130  is in a sector pair state and WT  1   124  is in a sector state. BS  1   102  may, and sometimes does, allocate the same tones to be used concurrently in sector B by WT  4   130  and by WT  1   124 . 
     The wireless terminals in a sector pair state, e.g., wireless terminal  4   130 , includes a plurality of antennas and are communicating in a MIMO mode of operation with the base station  102 .  FIG. 6  and  FIG. 7  provide more detailed exemplary illustrations. The sectors of the base station  102  are symbol timing synchronized facilitating such operations. 
       FIG. 2  is a drawing  200  of an exemplary base station  202  coupled to a multi-face receive antenna  204  and a multiple face transmit antenna  206  in accordance with various embodiments. In some embodiments, the same antenna is used for receive and transmit signaling. In this exemplary embodiment base station  200  is a three sector base station; however in other embodiments, the base station includes a different number of sectors, e.g., two, four, five, six, or more than six. 
     Exemplary base station  202  includes a wireless communications module  220 , a processor  226 , an I/O interface  228  and a memory  230  coupled together via a bus  231  over which the various elements may interchange data and information. Memory  230  includes routines  232  and data/information  234 . The processor  226 , e.g., a CPU, executes the routines  232  and uses the data/information  234  in memory  230  to control the operations of the base station  202  and implement methods, e.g., the method of flowchart  400  of  FIG. 4 . 
     Wireless communications module  220  communicates with a plurality of wireless terminals, wherein communication with an individual wireless terminal uses a number of faces determined by the state corresponding to the wireless terminal. For example, if the communication is uplink communication and the wireless terminal being communicated with is in a sector state, one antenna face of receive antenna faces ( 208 ,  210 ,  212 ) is used; however if the wireless terminal in a sector pair state  2  adjacent receive antenna faces are used, which is one of receive antenna face pairs ( 208 ,  210 ), ( 210 ,  212 ) and ( 212 ,  208 ). Continuing with the example, if the communication is downlink communication and the wireless terminal being communicated with is in a sector state, one antenna face of transmit antenna faces ( 214 ,  216 ,  218 ) is used; however if the wireless terminal in a sector pair state  2  adjacent transmit antenna faces are used, which is one of transmit antenna face pairs ( 214 ,  216 ), ( 216 ,  218 ) and ( 218 ,  214 ). 
     Wireless communications module  220  includes a wireless receiver module  222  and a wireless transmitter module  224 . The wireless receiver module  222 , e.g., a multi-sector OFDM receiver, is coupled to multi-face receive antenna  204  via which the base station receives uplink signals from wireless terminals. Multi-face receive antenna  204  is a three face receive antenna, each face ( 208 ,  210 ,  212 ) of said antenna  204  corresponding to a different sector of a cell. In this exemplary embodiment, the sectors are timing synchronized. Consider that receive antenna face ( 208 ,  210 ,  212 ) corresponds to sector (A, B, C), respectively. Antenna faces ( 208 ,  210 ) correspond to a first sector pair of (sector A and sector B); antenna faces ( 210 ,  212 ) correspond to a second sector pair of (sector B and sector C); antenna faces ( 212 ,  208 ) correspond to a third sector pair of (sector C and sector A). Wireless receiver module  222  receives uplink signals from wireless terminals. Receiver module  222  receives a signal using the same set of tones from two adjacent antenna faces. Operations of receiver module  222  include receiving a signal on a first set of tones from first antenna face, e.g., antenna face  208 , corresponding to the first sector, and concurrently receiving a signal on the first set of tones from the second antenna face, e.g., antenna face  210 , corresponding to the second sector. 
     Receiver module  222  also receives from a wireless terminal path loss information corresponding to multiple adjacent sectors. For example, receiver module  222  receives path loss information corresponding to a first antenna face in antenna face pair and path loss information corresponding to a second antenna face in the antenna face pair. For example, a wireless terminal may be situated in a region such that it can receive downlink signals from both transmit antenna face  214  and transmit antenna face  216 , and the wireless terminal receives pilot channel signals from each antenna face ( 214 ,  216 ) and generates a channel condition feedback report conveying path loss information, which is transmitted in uplink signals and received by receiver module  222 . In some embodiments, the received path loss information is a power measurement of a signal transmitted on a tone during a period of time during which the adjacent antenna face does not transmit on the same tone. For example, in one exemplary embodiment, at least one pilot tone signal transmitted into a first sector via one transmit antenna face corresponds, in time and frequency, to an intentional transmit null in a second sector, the first and second sectors being adjacent; and at least one pilot tone signal transmitted into the second sector via a second transmit antenna face, said second antenna face being adjacent said first antenna face, corresponds, in time and frequency, to an intentional transmit null in said first sector. 
     The wireless transmitter module  224 , e.g., a multi-sector OFDM transmitter, is coupled to multi-face transmit antenna  206  via which the base station transmits downlink signals to wireless terminals. Multi-face transmit antenna  206  is a three face transmit antenna, each face ( 214 ,  216 ,  218 ) of said antenna  206  corresponding to a different sector of a cell. In this exemplary embodiment, the sectors are timing synchronized. Consider that transmit antenna face ( 214 ,  216 ,  218 ) correspond to sector (A, B, C), respectively. Antenna faces ( 214 ,  216 ) correspond to a first sector pair of (sector A and sector B); antenna faces ( 216 ,  218 ) correspond to a second sector pair of (sector B and sector C); antenna faces ( 218 ,  214 ) correspond to a third sector pair of (sector C and sector A). Operations of wireless transmitter module  224  include transmitting downlink signals to wireless terminal. For example, the transmitter module  224  can, and sometimes does, transmit the same information from each of the antenna faces of a sector pair, e.g., antenna faces  214 ,  216 , to a first wireless terminal. During some times, the transmitter module  224  transmits different information to first and second wireless terminals using the same set of tones and using both antenna faces of antenna pair at the same time, said first and second wireless terminals each being in a sector pair state. 
     Routines  232  include a wireless terminal state information maintenance module  236 , a tone allocation module  238 , a tone hopping module  240 , a combiner module  242 , an extraction module  244 , a cancellation module  246 , an information recovery module  248 , a state determination module  250 , and a symbol time synchronization module  252 . Wireless terminal state information maintenance module  236  maintains information indicating whether a wireless terminal is in a sector or sector pair state for each of a plurality of wireless terminals in the base station&#39;s cell which are using the base station as a point of network attachment. 
     Tone allocation module  238  allocates sets of tones to wireless terminals. Tone allocation module  238  allocates a first set of tones for communication with a first wireless terminal in a sector pair state, the first set of tones being allocated to the first wireless terminal in each of a first and second sector of a sector pair. The tone allocation module  238  further allocates the first set of tones to a second wireless terminal in said first sector during at least a portion of time in which said first set of tones are allocated to the first wireless terminal. The second wireless terminal is in one of a sector state and a sector pair state. 
     Tone hopping module  240  hops sets of tones in a time synchronized manner in the sectors of the cell. For example, tone hopping module  240  hops a first set of tones over time in a time synchronized manner in a sector pair of the cell. In various embodiments, different hopping schemes are utilized for uplink and for downlink signals. In some embodiments, the downlink is hopped at a faster rate than the uplink is hopped. Tone hopping may, and sometimes does, represents hopping of indexed tones in a logical channel structure to indexed physical tones used for transmission purposes. 
     Combiner module  242  combines a signal received on a first antenna face with a signal received on a second antenna face. Extraction module  244  extracts a signal corresponding to one of a first and second wireless terminal from a combined signal from combiner module  242 , to recover at least some information transmitted by at least one of said first and second wireless terminals. Cancellation module  246  cancels the extracted signal from the signal received on one of the antenna faces to generate a processed signal. Information recovery module  248  recovers information communicated by the second wireless terminal from the processed signal. 
     State determination module  250  determines if a wireless terminal is in a sector state or sector pair state based on received path loss information, e.g., a channel condition feedback report corresponding to two adjacent sectors. Symbol time synchronization module  252  maintains symbol timing synchronization between the different sectors of the cell, e.g., OFDM symbol timing synchronization. 
     Data information  234  includes wireless terminal data/information  254  and timing frequency structure information  260 . Wireless terminal data/information  254  includes information corresponding to a plurality of wireless terminals using the base station as point of network attachment (WT  1  data information  256 , . . . , WT N data/information  258 ). WT  1  data/information  256  includes state information  262 , sector or sector pair identification information  264 , allocated tone set information  266 , path loss information corresponding to a 1 st  antenna face  272 , and path loss information corresponding to a 2 nd  antenna face  274 . Data/information  256  also includes one or more of recovered information being communicated  268  and information to transmit  270 . State information  262  includes information indicating whether wireless terminal  1  is in a sector state or sector pair state. State information  262  represents an output of state determination module  250 . Sector or sector pair identification information  264  includes information identifying, for a wireless terminal in a sector state, the sector, the transmit antenna face, and the receive antenna face to which the sector state corresponds. Sector or sector pair identification information  264  includes information identifying, for a wireless terminal in a sector pair state, the pair of adjacent sectors, the pair of adjacent transmit antenna faces, and the pair of receive antenna faces to which the sector pair state corresponds. Sector or sector pair identification information  264  also includes information identifying which sectors and antenna faces received path loss information corresponds to. Allocated tone set information  266  includes information identifying a set of tones currently allocated to wireless terminal  1  by tone allocation module  240 . The set of allocated tones can correspond to a downlink set of tones or an uplink set of tones. Path loss information corresponding to 1 st  antenna face  272  is, e.g., feedback information received from WT  1  indicative of channel conditions between a 1 st  antenna face and WT  1 . Path loss information corresponding to 2 nd  antenna face  274  is, e.g., feedback information received from WT  1  indicative of channel conditions between a 2 nd  antenna face and WT  1 , the second antenna face being adjacent said first antenna face. Path loss information ( 272 ,  274 ) is used by state determination module  250  in deciding the state for WT  1 , e.g., sector state or sector pair state. In general, for a wireless terminal near a sector boundary, the wireless terminal is in a sector pair state, while for a wireless terminal far away from a sector boundary the wireless terminal is in a sector state. 
     Recovered information being communicated  268  includes information output from extraction module  244  and/or information output from information recovery module  248 . 
     Timing/frequency structure information  260  includes downlink timing/frequency structure information and uplink timing frequency structure information. Downlink timing/frequency structure information includes information identifying and/or defining: downlink channel structure including logical channel segments, downlink frequency bands, downlink tone set information, subsets of tones which can be allocated to a wireless terminal, pilot signal information corresponding to each of the sectors, and downlink timing structure information including information defining symbol transmission timing intervals, groupings of symbols, e.g., into slots, superslots, beaconslots, ultraslots, etc., and recurring pattern information. 
     Uplink timing/frequency structure information includes information identifying and/or defining: uplink channel structure including logical channel segments, uplink frequency bands, uplink tone set information, subsets of tones which can be allocated to a wireless terminal, and uplink timing structure information including information defining symbol transmission timing intervals, groupings of symbols, e.g., into dwells and recurring pattern information. 
     Timing/frequency structure information  260  also includes tone hopping information  276 . In various embodiments, different tone hopping information is used for the downlink and the uplink. 
       FIG. 3  is a drawing of an exemplary wireless terminal  300 , e.g., mobile node, in accordance with various embodiments. Exemplary wireless terminal  300  is, e.g., one of the wireless terminals in system  100  of  FIG. 1 . Exemplary wireless terminal  300  is for use in a sectorized cell, each sector of said sectorized cell being adjacent at least one other sector in the cell, adjacent sectors forming sector pairs, the cell including a base station coupled to a multi-face antenna, each face of said base station antenna corresponding to a different sector of said cell, said sectors being timing synchronized. In some embodiments, the base station has three sectors. 
     Exemplary wireless terminal  300  includes a wireless receiver module  302 , a wireless transmitter module  304 , a processor  308 , user I/O devices  310  and memory  312  coupled together via bus  314  over which the various elements interchange data and information. Memory  312  includes routines  316  and data/information  318 . The processor  308 , e.g., a CPU, executes the routines  316  and uses the data/information  318  in memory  312  to control the operation of the wireless terminal  300  and implement methods, e.g., the method of flowchart  500  of  FIG. 5 . 
     Wireless terminal  300  also includes a plurality of antennas (antenna  1   303 , . . . , antenna N  305 ), and a duplex module  306 . The duplex module  303  couples one or more of the antennas (antenna  1   303 , . . . , antenna N  305 ) to wireless receiver module  302 . The duplex module  303  also couples one or more of the antennas (antenna  1   303 , . . . , antenna N  305 ) to wireless transmitter module  304 . In some other embodiments, different antennas are used for transmission and reception. 
     Wireless receiver module  302 , e.g., an OFDM receiver with MIMO capabilities, is used for receiving downlink signals from a base station. Wireless transmitter module  304 , e.g., an OFDM transmitter with MIMO capabilities, is used for transmitting uplink signals to a base station. Information transmitted by transmitter module  304  includes path loss information corresponding to a first antenna face of an antenna face pair and path loss information corresponding to a second antenna face in the antenna face pair, wherein said first and second antenna faces are adjacent antenna faces. Information transmitted by transmitter module  304  also includes uplink user data, e.g., uplink traffic channel segment data. 
     User I/O devices  310 , e.g., microphone, keypad, keyboard, mouse, camera, switches, speaker, display, etc., are used to receive input from the user of wireless terminal  300  and output information to the user of wireless terminal  300 . In addition, user I/O devices  310  allow a user of wireless terminal  300  to control at least some functions of the wireless terminal, e.g., initiate a communications session. 
     Routines  316  includes a state information maintenance module  320 , a mode determination module  322 , a MIMO module  324 , a non-MIMO mode module  326 , a tone allocation determination module  328 , a tone hopping module  330 , a state information recovery module  332 , a power measurement module  334 , and a path loss determination module  336 . State information maintenance module  320  maintains information indicating whether said wireless terminal is in a sector state or sector pair state. Mode determination module  322  determines whether the wireless terminal is to operate in a MIMO or non-MIMO mode of operation as a function of the maintained information indicating whether said wireless terminal is in a sector state or sector pair state. 
     MIMO module  324  is used for communicating with a base station when the wireless terminal  300  is in a MIMO mode of operation, as determined by module  322 . Non-MIMO mode module  326  is used for communicating with a base station when the wireless terminal  300  is in a non-MIMO mode of operation, e.g., a SISO mode of operation, as determined by module  322 . Modules  324  and  326  control various operations of wireless receiver module  302 , wireless transmitter module  304 , and duplex module  306  to implement a determined mode of operation. In various embodiments, communicating with a base station in a MIMO mode of operation includes using at least two wireless terminal antennas from the set of antennas ( 303 , . . . ,  305 ) in communications with two adjacent base station antenna faces. In some such embodiments, communicating with the base station in a MIMO mode of operation further includes using a first set of tones for communicating with both base station antenna faces of two adjacent base station antenna faces during the same time. 
     Tone allocation determination module  328  determines from received signal that a wireless terminal has been allocated a first set of tones for communicating. During some times, the tone allocation determination module  328  determines from received signals, e.g., received assignment signals, that the wireless terminal has been allocated a first set of tones for communication with both a first antenna face of the multi-face base station antenna and a second antenna face of the multi-face base station antenna, said first and second faces being adjacent. 
     Tone hopping module  330  uses stored information, e.g., stored tone hopping information  364  corresponding to base station  1  to implement tone hopping, wherein the first set of tones allocated to wireless terminal  300  are hopped over time in a synchronized manner in a sector pair. 
     State information recovery module  332  recovers from a received signal a base station determination indicating whether said wireless terminal is to be in a sector state or sector pair state, wherein said base station determination is based upon received path loss information communicated from the wireless terminal to the base station. 
     Power measurement module  334  performs a power measurement of a signal received on a tone during a period of time during which a first base station antenna face transmits a pilot tone signal and a second base station antenna face intentionally does not transmit on that tone, said first and second base station antenna faces being adjacent. This use of pilot signals from one base station antenna face intentionally paired with an intentional null from an adjacent base station antenna face, facilitates wireless terminal determination of path loss information with respect to individual base station antenna faces. Path loss determination module  336  determines path loss information as a function of power measurement information from module  334 . 
     Data/information  318  includes state information  338 , base station identification information  340 , sector or sector pair identification information  342 , allocated tone set information  344 , recovered information being communicated  346 , information to transmit  348 , pilot/sector null measurement information  350 , path loss information corresponding to a 1 st  antenna face  352 , path loss information corresponding to a 2 nd  antenna face  354 , and system data/information  356 . State information  338  includes information indicating whether the wireless terminal  300  is currently in a sector state or in a sector pair state. Base station identification information  340  includes information identifying which base station, from the plurality of base stations in the communications system, the wireless terminal is currently using as its point of network attachment. Sector or sector pair identification information  342  includes information identifying the particular sector of the base station for which tones are allocated to the wireless terminal when in the sector state and information identifying the pair of adjacent sectors of the base station for which tones are allocated to the wireless terminal for concurrent use when in the sector pair state. Information  342  also includes information identifying the sectors used to which the path loss information being communicated corresponds. Recovered information being communicated  346  includes user data recovered using a MIMO decoding operation of the receiver module  302  when the wireless terminal is in a sector pair state. Recovered information being communicated  346  also includes user data recovered using a SISO decoding operation of the receiver module  302  when the wireless terminal is in a sector state. Information to be transmitted  348  includes user data to be transmitted which is subjected to MIMO encoding operations by wireless transmitter module  304 , when the wireless terminal is in a sector pair state. Information to be transmitted  348  also includes user data to be transmitted which is subjected to SISO encoding operations by wireless transmitter module  304 , when the wireless terminal is in a sector state. 
     Pilot/sector null measurement information  350  represents output of power measurement module  334  and an input to path loss determination module  336 . Path loss information corresponding to 1 st  base station antenna face  352  and path loss information corresponding to 2 nd  base station antenna face  354  represents outputs of path loss determination module  336 . In some embodiments, the path loss information  352  is communicated independently from the path loss information  354 ; while in other embodiments, the information ( 352 ,  354 ) is transmitted in a jointly coded single report. In some embodiments, the report is a sector boundary report, e.g., as part of an uplink dedicated control channel reporting structure. 
     System data information  356  includes a plurality of sets of base station information (base station  1  data/information  358 , . . . , base station N data/information  360 ). Base station  1  data/information  358  includes base station identification information, base station sector identification information and timing/frequency structure information  362 . Timing frequency structure information  362  includes, e.g., downlink carrier frequency information, uplink carrier frequency information, downlink frequency band information, uplink frequency band information, downlink tone block information, uplink tone block information, individual tone definition information, recurring downlink timing information, recurring uplink timing information, OFDM symbol transmission timing information, information identifying grouping of OFDM symbols into, e.g., slots or dwells, downlink channel structure information and uplink channel structure information. Timing/frequency structure information  362  also includes tone hopping information  364 . Tone hopping information  364 , in some embodiments, includes different tone hopping information corresponding to the uplink and downlink. For example, the tone hopping, can be and sometimes is, different in both the hopping equations used and the rate of the hopping, e.g., tone hopping between successive OFDM transmission time intervals for the downlink and tone hopping based on dwells of seven successive OFDM symbol transmission time intervals for the uplink. 
       FIG. 4  comprising the combination of  FIG. 4A ,  FIG. 4B  and  FIG. 4C  is a flowchart  400  of an exemplary method of operating a base station in accordance with various embodiments. The base station is, e.g., a base station in a sectorized cell, each sector being adjacent at least one other sector in the cell, adjacent sectoring forming sector pairs, said base station being coupled to a multi-face antenna, each face of said antenna corresponding to a different sector or said cell, said sectors being timing synchronized. In some embodiments, the base station has three sectors. The base station is, e.g., base station  200  of  FIG. 2 . In some other embodiments, the base station has six sectors. Multi-sector base stations with different numbers of sectors are also possible. In various embodiments, said base station is a base station in an OFDM communications system and said timing synchronization is OFDM symbol time synchronization. 
     Operation of the exemplary method starts in step  402 , where the base station is powered on and initialized and proceeds to steps  404 ,  408 ,  410 , and  436 . Operation proceeds to step  404 , for each of a plurality of wireless terminals. In step  404 , the base station receives path loss information corresponding to a first antenna face in an antenna face pair, and in step  405 , the base station receives path loss information corresponding to a second antenna face in an antenna face pair. In various embodiments, the received path loss information is a power measurement of a signal transmitted on a tone during a time during which the adjacent antenna face does not transmit on said tone. For example, in some OFDM embodiments, there are at least some sector null and some corresponding pilot signals using the same tone at the same time in adjacent sectors. Operation proceeds from step  405  to step  406 , in which the base station determines if said wireless terminal is in a sector state or sector pair state based on the received path loss information. Wireless terminal state information  407 , identifying one of a sector state or sector pair state, is output from step  406  and input to step  408 . Operation proceeds from step  406  to step  404 , where the base station receives additional path loss information corresponding to the same wireless terminal. 
     In step  408 , which is performed for each of a plurality of wireless terminals, on an ongoing basis, the base station maintains information indicating whether the wireless terminal is in a sector state or sector pair state. 
     Operation proceeds from start step  402  to step  410  for a receive opportunity corresponding to a pair of wireless terminals. In step  410 , the base station allocates a first set of tones for communication with a first wireless terminal in said sector pair state, the first set of tones being allocated in each of a first and second sector of sector pair state. In some embodiments, the tones of the first set of tones are hopped in a synchronized manner in the sector pair. Operation proceeds from step  410  to step  412 . In step  412 , the base station allocates said first set of tones to a second wireless terminal in said first sector during at least a portion of time in which said first set of tones are allocated to the first wireless terminal. In some embodiments, the base station allocates said first set of tones to a second wireless terminal in said first sector during the same time in which said first set of tones are allocated to the first wireless terminal. Operation proceeds from step  412  via connecting node A  414  to step  416 . 
     In step  416  the base station communicates with wireless terminals, wherein communication with a particular wireless terminal uses a number of antenna faces determined by the state corresponding to the particular wireless terminal. In some such embodiments, the number is one or two. Step  416  includes sub-steps  418 ,  426 ,  428  and  434 . In sub-step  418 , the base station communicates with said first wireless terminal using two antenna faces. Sub-step  418  includes sub-steps  420 ,  422  and  424 . In sub-step  420 , the base station receives a signal on said first set of tones from a first antenna face corresponding to a first sector and concurrently receives a signal on said first set of tones from a second antenna face corresponding to a second sector. Then, in sub-step  422 , the base station combines the signal received from the first antenna face with the signal received from the second antenna face. Operation proceeds from sub-step  422  to sub-step  424 . In sub-step  424 , the base station extracts a signal corresponding to said first wireless terminal from said combined signal to recover at least some information communicated by the first wireless terminal. Operation proceeds from sub-step  418  to sub-step  426 . 
     In sub-step  426  the base station determines whether the second wireless terminal is in the sector state or sector pair state. If the second wireless terminal is in the sector state, then operation proceeds from sub-step  426  to sub-step  428 ; however, if the second wireless terminal is in the sector pair state, then operation proceeds from sub-step  426  to sub-step  434 . In sub-step  428  the base station communicates with said second wireless terminal using one antenna face. Sub-step  428  includes sub-step  430  and sub-step  432 . In sub-step  430 , the base station cancels the extracted signal, obtained in sub-step  424 , from the signal received on one of the antenna faces to generate a processed signal. Operation proceeds from sub-step  430  to sub-step  432 . In sub-step  432 , the base station recovers information communicated by the second wireless terminal from the processed signal. Returning to sub-step  434 , in sub-step  434 , the base station communicates with said second wireless terminal using two antenna faces. 
     Operation proceeds from start step  402  to step  436  for a transmit opportunity corresponding to a pair of wireless terminals. In step  436 , the base station allocates a second set of tones for communication with a third wireless terminal in said sector pair state, the second set of tones being allocated in each of a first and second sector of sector pair state. In some embodiments, the second set of tones are hopped over time in a synchronized manner in the sector pair. Operation proceeds from step  436  to step  438 . In step  438 , the base station allocates said second set of tones to a fourth wireless terminal in said first sector during at least a portion of time in which said second set of tones are allocated to the third wireless terminals. In some embodiments, the base station allocates said second set of tones to a fourth wireless terminal in said first sector during the same time in which said second set of tones are allocated to the third wireless terminals. Operation proceeds from step  438  via connecting node B  440  to step  441 . 
     In step  441  the base station communicates with wireless terminals, wherein communication with a particular wireless terminal uses a number of antenna faces determined by the state corresponding to the particular wireless terminal. Step  441  includes sub-steps  442 ,  446 ,  448  and  452 . In sub-step  442 , the base station communicates with said third wireless terminal using two antenna faces. Sub-step  442  includes sub-step  444 . In sub-step  444 , the base station transmits the same information from each of two antenna faces to said third wireless terminal using the second set of tones. 
     In sub-step  446  the base station determines whether the fourth wireless terminal is in the sector state or sector pair state. If the fourth wireless terminal is in the sector state, then operation proceeds from sub-step  446  to sub-step  448 ; however, if the fourth wireless terminal is in the sector pair state, then operation proceeds from sub-step  446  to sub-step  452 . In sub-step  448  the base station communicates with said fourth wireless terminal using one antenna face. Sub-step  448  includes sub-step  450 . In sub-step  450 , the base station transmits to the fourth wireless terminal using one antenna face and using the second set of tones. Returning to sub-step  452 , in sub-step  452 , the base station communicates with said fourth wireless terminal using two antenna faces. Sub-step  452  includes sub-step  454 . In sub-step  454 , the base station transmits different information to the fourth wireless terminal than the information being transmitted to the third wireless terminal using the second set of tones and uses both faces of the antenna pair at the same time. 
       FIG. 5  comprising the combination of  FIG. 5A  and  FIG. 5B  is a flowchart  500  of an exemplary method of operating a wireless terminal in accordance with various embodiments. The exemplary wireless terminal is a wireless terminal in a sectorized cell, each sector being adjacent at least one other sector in the cell, adjacent sectors forming sector pairs, the cell including a base station, e.g., a three sector base station, coupled to a multi-face antenna, each face of said base station antenna corresponding to a different sector of the cell, said sectors being timing synchronized. The exemplary wireless terminal includes at least two antennas and supports MIMO signaling. In various embodiments, the wireless terminal is part of an OFDM wireless communications system and the sectors of a cell corresponding to a base station are OFDM symbol timing synchronized Operation starts in step  502 , where the wireless terminal is powered on and initialized and proceeds to step  504 . Operation proceeds from start step  502  to step  504 , step  508 , step  526  via connecting node A  510 , and step  540  via connecting node B  512 . 
     In step  526 , the wireless terminal performs power measurements of pilot tone signals and sector null signals. Step  526  includes sub-steps  528  and  530 . In sub-step  528 , the wireless terminal performs a power measurement of a signal received on a tone during a period of time during which a first base station antenna face transmits a pilot tone signal and a second base station antenna face intentionally does not transmit on that tone, said first and second antenna faces being adjacent. In sub-step  530 , the wireless terminal performs a power measurement of a signal received on a tone during a period of time during which said second base station antenna face transmits a pilot tone signal and said first base station antenna face intentionally does not transmit on that tone. Operation proceeds from step  526  to step  532 , in which the base station determines path loss information as a function of said power measurement information. Operation proceeds from step  532  to step  534 . In step  534 , the base station transmits path loss information. Step  534  includes sub-step  536  and sub-step  538 . In sub-step  536 , the base station transmits path loss information corresponding to said first base station antenna face and in step  538 , the base station transmits path loss information corresponding to said second base station antenna face, said first and second base station antenna faces being part of antenna pair face. In some embodiments, path loss information corresponding to the first antenna face is transmitted independently of the path loss information corresponding to the second antenna face. In some embodiments, path loss information corresponding to the first antenna face is communicated in the same report as path loss information corresponding to the second antenna face. 
     Returning to step  504 , in step  504 , which is performed on an ongoing basis, the wireless terminal monitors for state assignment signals. Operation proceeds from step  504  to step  506  for a received state assignment signal intended for the wireless terminal. In step  506 , the wireless terminal receives a base station determination as to whether said wireless terminal is to be in a sector state or sector pair state. The base station determination is based upon received path loss information from the wireless terminal. WT state information  507 , e.g., an indication of either sector state or sector pair state, is an output from step  506  which is used an input in step  508 . 
     In step  508 , which is performed on an ongoing basis, the wireless terminal maintains information indicating whether said wireless terminal is in a sector state or sector pair state. Operation proceeds from step  508  to step  514 . In step  514 , the wireless terminal communicates with said base station in one of a MIMO mode of operation and a non-MIMO mode of operation, the mode of operation used for communication being a function of whether said maintained information indicates that said wireless terminal is in a sector state or sector pair state. Step  514  includes sub-steps  516 ,  518  and  520 . 
     In sub-step  516 , the wireless terminal checks if the wireless terminal is in a sector state or sector pair state. If the wireless terminal is determined to be in a sector pair state operation proceeds from sub-step  516  to sub-step  518 ; otherwise operation proceeds from sub-step  516  to sub-step  520 . In sub-step  518 , the wireless terminal communicates with said base station in a MIMO mode of operation. Sub-step  518  includes sub-steps  522  and  524 . In sub-step  522 , the wireless terminal uses at least two wireless terminal antennas to communicate with two adjacent base station antenna faces. In sub-step  524 , the wireless terminal uses a first set of tones to communicate with both faces of said two adjacent base station antenna faces during the same time. Returning to step  520 , in step  520 , the wireless terminal communicates with the base station in a non-MIMO mode of operation, e.g., a SISO mode of operation or a mode of operation or a mode of operation using two or more wireless terminal antennas communicating with a single base station antenna face. 
     Returning to step  540 , in step  540 , which is performed on an ongoing basis, the wireless terminal monitors for tone allocation information. Operation proceeds from step  540  to step  542  in response to detected tone allocation information intended for the wireless terminal. In step  542 , the wireless terminal receives tone allocation information indicating that said wireless terminal has been allocated a first set of tones. Step  542  includes sub-step  544  for some tone allocations, e.g., a tone allocation when said wireless terminal is in a sector pair state. In sub-step  544 , the wireless terminal receives tone allocation information indicating that said wireless terminal has been allocated a first set of tones for communication with both a first antenna face of said multi-face base station antenna and second antenna face of said multi-face base station antenna, said first and second antenna faces being adjacent. In various embodiments, the first set of tones are hopped in a time synchronized manner in the sector pair. 
       FIG. 6  is a drawing  600  illustrating an exemplary embodiment corresponding system  100  of  FIG. 1  in which WT  4   130  includes two antennas (antenna  1   602 , antenna  2   604 ). Communications  144  between base station sector B antenna face  120  and WT  4   130  includes a first portion  144   a  corresponding to antenna  1   602  and a second portion  144   b  corresponding to antenna  2   604 . Similarly, communications  146  between base station sector C antenna face  122  and WT  4   130  includes a first portion  146   a  corresponding to antenna  1   602  and a second portion  146   b  corresponding to antenna  2   604 . 
       FIG. 7  is a drawing  700  illustrating an exemplary embodiment corresponding system  100  of  FIG. 1  in which WT  4   130  includes three antennas (antenna  1   702 , antenna  2   704 , antenna  3   706 ). Communications  144  between base station sector B antenna face  120  and WT  4   130  includes a first portion  144   c  corresponding to antenna  1   702 , a second portion  144   d  corresponding to antenna  2   704 , and a third portion  144   e  corresponding to antenna  3   706 . Similarly, communications  146  between base station sector C antenna face  122  and WT  4   130  includes a first portion  146   c  corresponding to antenna  1   702 , a second portion  146   d  corresponding to antenna  2   704 , and a third portion  146   e  corresponding to antenna  3   706 . Embodiments, with wireless terminals having more than three antennas are also possible. 
       FIG. 8  is a drawing  800  illustrating exemplary air link resources corresponding to different sectors of a base station and exemplary tone allocation to wireless terminals in accordance with various embodiments. Drawing  800  includes a first graph  802  corresponding to sector A, a second graph  804  corresponding to sector B, and a third graph  806  corresponding to sector C. Each graph ( 802 ,  804 ,  806 ) includes a vertical axis  810  representing frequency, e.g., OFDM tone index in frequency band A, and a horizontal axis  812  of time, e.g., OFDM symbol index. It should be noted that the three sectors of the base station are synchronized in terms of both time and frequency. In this exemplary embodiment, tone hopping, e.g., in terms of logical channel tone index designation to physical tone index designation, is also synchronized with respect to the sectors. 
     Block  814  in graph  802  represents 64 basic units of air link resources, e.g., 64 OFDM tone-symbols, used by sector A and illustrates exemplary allocation of those resources. Block  816  in graph  804  represents 64 basic units of air link resources, e.g., 64 OFDM tone-symbols, used by sector B and illustrates exemplary allocation of those resources. Block  818  in graph  806  represents 64 basic units of air link resources, e.g., 64 OFDM tone-symbols, used by sector A and illustrates exemplary allocation of those resources. 
     Legend  808  indicates that a tone-symbol allocated to WT  2 , which is in sector pair state with the sectors of the pair being A and C, is indicated by diagonal line shading with descending slope from left to right as shown in example small block  820 . Legend  808  indicates that a tone-symbol allocated to WT  3 , which is in sector pair state with the sectors of the pair being A and C, is indicated by diagonal line shading with ascending slope from left to right as shown in example small block  822 . Legend  808  indicates that a tone-symbol allocated to WT  4 , which is in sector pair state with the sectors of the pair being B and C, is indicated by horizontal line shading as shown in example small block  824 . Legend  808  indicates that a tone-symbol allocated to WT  5 , which is in sector state with the sector being C, is indicated by vertical line shading as shown in example small block  826 . Legend  808  indicates that a tone-symbol allocated to WT  1 , which is in sector state with the sector being B, is indicated by dotted shading as shown in example small block  828 . 
       FIG. 9  is a drawing  900  illustrating sector nulls corresponding to pilot tones in an exemplary OFDM wireless communications system implementing synchronized sectors. Drawing  800  includes a first graph  902  corresponding to sector A, a second graph  904  corresponding to sector B, and a third graph  906  corresponding to sector C. Each graph ( 902 ,  904 ,  906 ) includes a vertical axis  910  representing frequency, e.g., OFDM tone index in downlink frequency band, and a horizontal axis  912  of time, e.g., OFDM symbol index. It should be noted that the three sectors of the base station are synchronized in terms of both time and frequency. 
     Block  914  in graph  902  represents 64 basic units of air link resources, e.g., 64 OFDM tone-symbols, used by sector A and illustrates exemplary allocation of those resources with regard to pilot tone signals and intentional nulls. Block  916  in graph  904  represents 64 basic units of air link resources, e.g., 64 OFDM tone-symbols, used by sector B and illustrates exemplary allocation of those resources with regard to pilot tone signals and intentional nulls. Block  918  in graph  906  represents 64 basic units of air link resources, e.g., 64 OFDM tone-symbols, used by sector C and illustrates exemplary allocation of those resources with regard to pilot tone signals and intentional nulls. 
     Legend  908  indicates that a tone-symbol allocated to convey a pilot tone signal is represented by a small box including an O, as shown in example element  920 ; while a tone-symbol allocated to convey an intentional sector null is represented by a small box including an X, as shown in example element  922 . 
     In various embodiments one or more channel quality measurements and/or indicators are used by state determination module  250  in deciding the state for a wireless terminal WT, e.g., sector state or sector pair state. In the above description, the channel quality indicator used by the state determination module  250  has been described as path loss information. However, other types of channel quality information may, and in some embodiments are, used in the place of path loss information. Consider for example SNR measurements which are used in the place of path loss information by the state determination module  250  in making the state determination in some embodiments. Such an embodiment is particularly well suited when an uplink transmission SNR value is available for use. In such a case, the SNR value is dependent on path loss but may also be dependent on other factors such as sector interference. The SNR may, and in some embodiments is, measured separately from sector interference measurements. Sector interference is an example of a channel quality measurement upon which the state determination may be made instead of path loss however, as can be appreciated, other channel quality indicates may be used instead or in addition to SNR and/or path loss information. 
     It should also be appreciated that while determining path loss has been described in the above example as being done, at least in some embodiments by measuring path loss through the use of sector pilots and/or sector nulls other approaches may be used for determining path loss. For example, in some embodiments rather than have the mobile determine and communicate path loss information to the base station, the base station may determine path loss by monitoring one or more persistent, periodic or otherwise recurring uplink signals from the mobile transmitted at, e.g., a power level known to the base station. In one particular embodiment, the base station monitors a dedicated uplink control channel between the mobile and the base station and estimates path loss based on measurements of signals received from the mobile node which correspond to the dedicated uplink control channel. Other base station centric ways of measuring and/or estimating path loss could be used depending on the particular embodiment and the above examples are intended to facilitate an understanding of various embodiments but not limit the scope of subject matter thereto. 
     While described in the context of an OFDM system, the methods and apparatus of various embodiments are applicable to a wide range of communications systems including many non-OFDM and/or non-cellular systems. 
     In various embodiments nodes described herein are implemented using one or more modules to perform the steps corresponding to one or more methods, for example, maintaining information indicating a sector state or sector pair state, communicating with a wireless terminal using a number of base station antenna faces determined by the state corresponding to the wireless terminal, determining a state for a wireless terminal as a function of received path loss information, maintaining timing synchronization between sectors, transmitting pilots in conjunction with sector nulls, etc. In some embodiments various features are implemented using modules. Such modules may be implemented using software, hardware or a combination of software and hardware. Many of the above described methods or method steps can be implemented using machine executable instructions, such as software, included in a machine readable medium such as a memory device, e.g., RAM, floppy disk, etc. to control a machine, e.g., general purpose computer with or without additional hardware, to implement all or portions of the above described methods, e.g., in one or more nodes. Accordingly, among other things, various embodiments are 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). 
     In some embodiments, the processor or processors, e.g., CPUs, of one or more devices, e.g., communications devices such as wireless terminals are configured to perform the steps of the methods described as being as being performed by the communications device. Accordingly, some but not all embodiments are directed to a device, e.g., communications device, with a processor which includes a module corresponding to each of the steps of the various described methods performed by the device in which the processor is included. In some but not all embodiments a device, e.g., communications device, includes a module corresponding to each of the steps of the various described methods performed by the device in which the processor is included. The modules may be implemented using software and/or hardware. 
     Numerous additional variations on the methods and apparatus described above will be apparent to those skilled in the art in view of the above descriptions. Such variations are to be considered within scope. The methods and apparatus of various embodiments 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. In some embodiments the access nodes are implemented as base stations which establish communications links with mobile nodes using OFDM and/or CDMA. In various embodiments 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 various embodiments.

Technology Category: 5