Patent Publication Number: US-2004053634-A1

Title: Adaptive pointing for use with directional antennas operating in wireless networks

Description:
RELATED APPLICATION(S)  
     [0001] This application claims the benefit of U.S. Provisional Application No. 60/377,458, filed on May 2, 2002, U.S. Provisional Application No. 60/378,156, filed on May 14, 2002, U.S. Provisional Application No. 60/378,157, filed on May 14, 2002, and U.S. Provisional Application No. 60/377,911, filed on May 3, 2002. The entire teachings of the above applications are incorporated herein by reference. 
    
    
     
       BACKGROUND OF THE INVENTION  
       [0002] Code Division Multiple Access (CDMA) modulation may be used to provide wireless communication between a base station and one or more field units. In CDMA cellular systems, multiple field units may transmit and receive signals on the same frequency but with different codes to permit detection of signals on a per unit basis. A typical field unit is a digital cellular telephone handset or a personal computer coupled to a cellular modem.  
       [0003] The base station is typically a computer controlled set of transceivers that are interconnected to a land-based public switched telephone network (PSTN) or in the case of a data system, an Internet gateway such as through an Internet Service Provider (ISP). The base station includes an antenna apparatus for sending forward link radio frequency signals to the field units. The base station antenna is also responsible for receiving reverse link radio frequency signals transmitted from each field unit. Each field unit also contains an antenna apparatus for the reception of the forward link signals and for transmission of the reverse links signals.  
       [0004] The most common type of antenna used to transmit and receive signals at a field unit is a mono-pole or omni-directional antenna. This type of antenna consists of a single wire or antenna element that is coupled to a transceiver within the field unit. The transceiver receives reverse link signals to be transmitted from circuitry within the field unit and modulates the signals onto the antenna element at a specific frequency assigned to that field unit. Forward link signals received by the antenna element at a specific frequency are demodulated by the transceiver and supplied to processing circuitry within the field unit.  
       [0005] The signal transmitted from a monopole antenna is omnidirectional in nature. That is, the signal is sent with the same signal strength in all directions in a generally horizontal plane. Reception of a signal with a monopole antenna element is likewise omni-directional. A monopole antenna does not differentiate in its ability to detect a signal in one direction versus detection of the same or a different signal coming from another direction.  
       [0006] A second type of antenna which may be used by field units is described in U.S. Pat. No. 5,617,102. The system described therein provides a directional antenna comprising two antenna elements mounted on the outer case of a laptop computer. The system includes a phase shifter attached to the two elements. The phase shifter may be switched on or off in order to affect the phase of signals transmitted or received during communications to and from the computer. By switching the phase shifter on, the antenna transmit pattern may be adapted to a predetermined hemispherical pattern which provides transmit beam pattern areas having a concentrated signal strength or gain. The dual element antenna directs the signal into predetermined quadrants or hemispheres to allow for large changes in orientation relative to the base station while minimizing signal loss.  
       [0007] CDMA cellular systems are also recognized as being interference limited systems. That is, as more field units become active in a cell and in adjacent cells, frequency interference becomes greater and thus error rates increase. As error rates increase, maximum data rates decrease. Thus, another method by which data rate can be increased in a CDMA system is to decrease the number of active field units, thus clearing the airwaves of potential interference. For instance, to increase a current maximum available data rate by a factor of two, the number of active field units can be decreased by one half. However, this is rarely an effective mechanism to increase data rates due to a lack of priority amongst users.  
       SUMMARY OF THE INVENTION  
       [0008] Both simulation and field measurements have shown that operations of directional antennas in frequency duplexed systems operating in interference/multi-path environments can be contradictory. In other words, since transmit and receive frequencies are different and because interference can come from any direction, the optimum settings for a directional antenna may not be the same for a forward link as for a reverse link. Consideration should be given to optimizing the forward link operation, while still achieving a suitable reverse link. Because of this, some sort of process is needed to determine the best antenna settings when attempting to set-up the reverse link.  
       [0009] To optimize reception of the forward link signal, the antenna apparatus can be pointed via phase or mechanical steering techniques at the angle which gives the largest signal-to-noise ratio (E s /N o ), where E s  is defined as energy per symbol and N o  is defined as total noise in dB. This is because E s /N o  is the main metric that defines overall system performance. If a better E s /N o  ratio is achieved, the amount of power supplied to a user to support the same data throughput can be reduced. But, in many cases, pointing based on only E s /N o  can result in a significant degradation in reverse link performance. This is because pointing based on E s /N o  may steer the antenna beam at an angle away from the base station with which the field unit is communicating to reduce interference from a base station in an adjacent cell. Thus, when using an antenna apparatus associated with most low-cost portable antenna arrays that do not allow for separate and independent pointing beams for transmit and receive, the communications in the forward link will be optimized, but the communications in the reverse link may not be optimized for the same antenna direction selection. To maximize overall communications performance in both forward and reverse directions, direction selection should also be based on a metric associated with optimized performance in the reverse link, such as pilot power.  
       [0010] Accordingly, the present invention provides a technique that can be used to point a directional antenna based on a ranking process. The ranking process of choice may use both E s /N o  and Pilot Power parameters as measured from a pilot signal. Using this pointing and ranking process enables adaptive pointing of directional antennas in interference and multi-path driven environments where there is only one antenna beam to point for both transmit and receive links. This is especially useful for an application where transmit and receive links are separated (i.e., duplexed) in frequency.  
       [0011] In addition to selecting antenna angle settings based on metrics associated with good forward and reverse link performance, the system may use this process for initial base station acquisition or start it after establishing a link with a base station, for example, in omni-directional mode. In addition, weights may be combined with the metrics to account for various environments or directional factors.  
       [0012] Various phenomena directly affect the performance of antenna pointing processes. These phenomena may be different from one environment to another and may include severity of multi-path, amount of interference, and Root-Mean-Square (RMS) delay spread.  
       [0013] In one embodiment, the angle settings may be fine tuned for use with directional antenna pointing systems that operate in different environments. The fine tuning applies adjustment factors or weights to the metrics used in determining the angle settings to maximize the performance of the directional antenna in any environment.  
       [0014] In addition to the environmental weights, a system employing the principles of the present invention may include weights associated with the antenna pattern. An example of such weights is an Antenna Pattern Correlation Factor (CF), which can be used independent of or in conjunction with other processes to improve directional antenna pointing. The CF is the result of a comparison of patterns that can be, but are not limited to, expressions in discrete or continuous form. The comparison can be performed by discrete or continuous convolution or by some other comparison technique such as, but not limited to, least mean square. The use of CF allows for selection of the “best” pointing direction even when the metric varies significantly at different pointing angles.  
       [0015] The independent use of the CF allows for finding the center of mass of the “best” received pilot power signal, signal-to-noise ratio, frame error rate, delay spread, and other receiver signal metrics. Using the CF in conjunction with another weighting process allows for weighting of various metrics within the process, such as weighting based on multi-path severity. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0016] The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
     [0017]FIG. 1 is a block diagram of a system which employs two different types of channel encoding;  
     [0018]FIG. 2 illustrates a cell of a CDMA cellular communications system using a directional antenna apparatus;  
     [0019]FIG. 3 illustrates a preferred configuration of the directional antenna apparatus used by a field unit in the cellular communications system of FIG. 2;  
     [0020]FIG. 4 illustrates an alternative configuration of the directional antenna apparatus used by the field unit in FIG. 3;  
     [0021]FIG. 5 is a system diagram of the communications system of FIG. 2 depicting the field unit with directional antenna patterns;  
     [0022]FIG. 6 is a circuit diagram used by the field unit to determine metrics used to select one of the antenna angles of FIG. 5;  
     [0023]FIG. 7 is a generalized flow diagram of a process used by the field unit for selecting the angle setting based on the metrics of FIG. 6;  
     [0024]FIG. 8 is a flow diagram used by the process of FIG. 7 for selecting and ranking the angle settings;  
     [0025]FIG. 9A is a detailed flow diagram of a first aspect of the process of FIG. 7;  
     [0026]FIG. 9B is a detailed flow diagram of a second aspect of the process of FIG. 7;  
     [0027]FIG. 10 is a flow diagram of a process used to calculate weights for optional use by the process of FIG. 7;  
     [0028]FIG. 11 is a theoretical free space directional antenna pattern replicated ten times using ten different reference positions for use by the process of FIG. 10;  
     [0029]FIG. 12 is a theoretical free space directional antenna pattern and a superimposed theoretically measured pilot power pattern for use by the process of FIG. 10; and  
     [0030]FIG. 13 is a plot of an actual measured free space antenna pattern and a measured pilot power pattern annotated with arrows for which calculations may be made for calculating a maximum Correlation Factor (CF) applied as a weight in FIG. 10. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
     [0031] A description of preferred embodiments of the invention follows.  
     [0032]FIG. 1 is a block diagram of a Code Division Multiple Access (CDMA) communications system  10 . The communications system  10  is described such that the shared channel resource is a wireless or radio channel. Although depicted as a cellular communications network, it should be understood that the techniques described herein can be applied to other wireless networks, such as Wireless Local Area Networks (WLAN&#39;s).  
     [0033] The system  10  supports wireless communications for a first group of users  20  as well as a second group of users  30 . The first group of users  20  are typically legacy users of cellular telephone equipment, such as wireless handsets  40 - 1 ,  40 - 2 , and/or cellular mobile telephones  40 -k installed in vehicles. This first group of users  20  principally use the network in a voice mode whereby their communications are encoded as continuous transmissions. The users&#39; transmissions are forwarded from the subscriber units  40  through forward link  50  radio channels and reverse link  60  radio channels. Their signals are managed at a central location that includes a base station antenna  70 , base transceiver station (BTS)  72 , and base station controller (BSC)  74 . The first group of users  20  are therefore typically engaged in voice conversations using the field units  40 , BTS  72 , and BSC  74  to connect telephone connections through a Public Switch Telephone Network (PSTN)  76 .  
     [0034] The communications system  10  also includes a second group of users  30 . This second group of users  30  are typically users who require high speed wireless data services. Their system components include a number of remotely located Personal Computer (PC) devices  80 - 1 ,  80 - 2 , . . .  80 -h, . . .  80 - 1 , corresponding remote Access Terminals (ATs)  82 - 1 ,  82 - 2 , . . .  82 -h, . . .  82 - 1 , and associated antennas  84 - 1 ,  84 - 2 , . . .  84 - h , . . .  84 - 1 . Centrally located equipment includes a base station antenna  90  and a Base Station Processor (BSP)  92 . The BSP  92  provides connections to and from an Internet gateway  96 , which in turn provides access to a data network such as the Internet  98 , and network file server  100 .  
     [0035] The operation of a system that allows for multi-user orthogonal and non-orthogonal interoperability of code channels that supports the two groups of users is described in International Publication Number WO 02/09320, the entire teachings of which are incorporated herein by reference.  
     [0036]FIG. 2 illustrates a cell of a CDMA cellular communications system using a directional antenna apparatus. The field units  210 - 1  through  210 - 3  with respective antennas  220  provide directional reception of forward link radio signals transmitted from base station  230  with antenna  240 , as well as providing directional transmission of reverse link signals, via a process called beamforming, from the field units  210  to the base station  230 . Beamforming may be performed by directional antenna arrays that include active antenna elements or combination of active and passive antenna elements.  
     [0037]FIG. 3 illustrates a detailed isometric view of a mobile subscriber unit  210  and one type of associated antenna apparatus  300 . The antenna apparatus  300  includes a platform or housing  310  upon which five antenna elements  301  through  305  are mounted. Within the housing  310 , the antenna apparatus  300  includes phase shifters  320  through  324 , a bi-directional summation network or splitter/combiner  330 , transceiver  340 , and control processor  350 , which are all interconnected via a bus  360 .  
     [0038] As illustrated, the antenna apparatus  300  is coupled via the transceiver  340  to a laptop computer  80  (not drawn to scale). This phase array type antenna apparatus  300  allows the laptop computer  80  to perform wireless data communications via forward link signals  50  transmitted from a base station  90  and reverse link signals  60  transmitted to the base station  90 .  
     [0039]FIG. 4 illustrates a detailed isometric view of a field unit  210  and another antenna apparatus  400 . This antenna apparatus  400  is an alternative embodiment of the previously discussed antenna apparatus  300  (FIG. 3). In contrast to the earlier presented antenna apparatus  300 , this antenna apparatus  400  employs multiple passive antenna elements  401  through  405  that are electromagnetically coupled (i.e., mutually coupled) to a centrally located active antenna element  406 . The passive antenna elements  401  through  405  re-radiate electromagnetic energy, which affects the direction from/to which the active antenna element  406  receives/transmits RF signals, respectively. The direction of the antenna pattern (not shown) is affected by the phase of the individual passive antenna elements  401 - 405 , which are set by selectable impedance components  410 - 414 , respectively. The laptop computer  80  or specialized processor (not shown) in the laptop computer  80 , antenna apparatus  400 , or separate device may be used to determine the setting for each of the selectable impedance components  410 - 414  to control the angle setting of the antenna pattern produced by the antenna apparatus  400 .  
     [0040]FIG. 5 is a network diagram of the field unit  210  communicating with base stations (not shown) associated with base station antenna towers  520  and  530 . The field unit  210  has a directional antenna  400  (FIG. 4) that is capable of providing an antenna pattern at a first antenna beam angle  505  and second antenna beam angle  510 . It should be understood that the directional antenna  400  is capable of providing many more beam angles; the first and second antenna beam angles  505 ,  510 , respectively, are shown for exemplary purposes.  
     [0041] The field unit  210  may start a scan with the antenna beam pointed in the first antenna beam angle  505  directly at the first antenna tower  520 . Forward link signals are sent from the first antenna tower  520  to the field unit  210  along a first transmission path  515 . At the same time, the second antenna tower  530  si sending forward link signals to the field unit  210  along a second transmission path  525 . While receiving signals along the first transmission path  515  from the first antenna tower  520 , the field unit  210  receives the forward link signals from the second antenna tower  530 , which may be considered interference or noise, since the first antenna beam  505  has some gain in the direction of the second transmission path  525 .  
     [0042] To reduce the interference from the second antenna tower  530 , the field unit  210  scans the antenna beam from the first antenna beam angle  505  to the second antenna beam angle  510 . In this way, the transmissions from the second antenna tower  530  along the second transmission path  525  are reduced since there is little to no gain in the antenna beam pattern at the second antenna beam angle  510  in the direction of the second transmission path  525 . This results in a loss of some gain for receiving signals from the first antenna tower  520  (e.g., 5 dB loss) and, understandably, loss in reverse link signal gain from the field unit  210  to the first antenna tower  520 .  
     [0043] However, it should be appreciated that overall, the communications between the field unit  210  and the first antenna tower  520  may be improved due to the reduction of interference from the signals received from the second antenna tower  530 . Thus, by using metrics, such as E s /N o  and pilot power, respectively associated with good performance in both the forward and reverse links, an overall improvement in communications performance may be achieved in the face of interference and multipath. In other words, selecting an angle setting suboptimal in one link direction may improve performance in the other link direction for improved overall performance of the field unit  210 .  
     [0044]FIG. 6 provides an example processor  600 , or part thereof, for determining metrics associated with the forward and reverse links. In this case, the processor  600  outputs (i) a first metric, calculated as a function of noise, such as the Pilot E s /N o , and (ii) a second metric, such as Pilot Power (PilotPwr).  
     [0045] Referring to the processor  600 , a received channel from the base transceiver station (BTS) is received by a variable gain amplifier (VGA)  605 . The output of the VGA  605  is received by a detector  610 , which provides a signal to an automatic gain control (AGC) controller  615 . The AGC controller  615  outputs a control voltage as feedback to the VGA  605 .  
     [0046] The output of the VGA  605  is also received by a pilot demodulator  620 . The pilot demodulator outputs a signal E s /N o , which may be representative of the energy per symbol divided by the total noise in the pilot channel. This signal is multiplied by the control voltage through use of a multiplier  625 . Since the control voltage represents energy of the received channel, the resultant signal is the Pilot Power.  
     [0047] It should be understood that there is additional circuitry, not shown, that is used to isolate the Pilot channel from among the orthogonal channels sent in the forward link from the BTS to the field unit  210  in which this processor  600  is deployed.  
     [0048]FIG. 7 is a flow diagram of a process  700  that illustrates alternative uses or timings in which the identification and selection of angle settings may be applied. This process  700  describes a “best angle selection” subprocess  702  and a “best base station selection” subprocess  704 . In the best angle selection subprocess  702 , the process  700  is already associated with a base station, and the process  700  identifies a best angle setting for the directional antenna to communicate with that base station, balanced for good performance in both forward and reverse links, as described above. In the best base station selection subprocess  704 , the process  700  uses the scanning capability of the antenna to assist in searching for a “best” base station with which to communicate.  
     [0049] Referring to the process  700 , after the process  700  has started (step  705 ), a determination is made as to whether to use directional mode of the antenna to locate a “best” base station (step  710 ) or to select a base station in omni-directional mode as is traditionally done. If the traditional method of locating a base station is selected, such as through identification of the pilot signal with the best signal-to-noise ratio (SNR), the process  700  sets its directional antenna to omni-directional mode (step  715 ) and locates a base station  720  based on measurements of a Pilot signal(s) that it receives from one or more base stations (step  720 ). Once a base station has been selected in omni-directional mode, the field unit  210  sets the directional antenna to a directional mode (step  725 ) and performs a scan to determine angle setting rankings of each of the angle settings associated with the directional antenna (step  730 ). As discussed above, determining the angle setting rankings is done as a function of a metric associated with the forward link and a metric associated with a reverse link between the base station and field unit  210 .  
     [0050] Using the angle setting rankings, the field unit  210  may attempt to connect in the reverse link to the base station using the highest ranked angle setting (step  735 ). If the connection is successful (step  740 ), then the process is complete (step  770 ). If the connection is not successful (step  740 ), then the field unit  210  uses the directional antenna and attempts to connect to the base station using the next highest ranked angle setting (step  735 ). This process of attempting to use the next highest ranked angle setting (step  735 ) continues until a connection with the base station located in omni-directional mode  715  by the field unit has been successful or results in the field unit connecting to the base station in omni-directional mode, a step which is not shown but is used as a default should directional mode connection fail.  
     [0051] If the field unit  210  uses directional mode to locate a “best” base station (step  710 ) using the other subprocess  704 , the process  700  sets the directional antenna  400  to directional mode (step  745 ). The process  700  performs a scan using the directional antenna and determines base station rankings through use of the angles in the scan (step  750 ). The base station rankings may be assigned as a function of the signal-to-noise (SNR) of the respective pilot signals of the base stations, as identified at each of the scan angles.  
     [0052] Once the scan is complete, the field unit  210 , using the subprocess  704 , attempts to connect to the highest ranked base station (step  755 ). If the connection is successful (step  760 ), the process  700  continues by either ending (step  770 ) or performing an optional step of optimizing the scan angle for the selected base station by using the scan and angle setting ranking process ( 765 ), similar to steps  735  and  740  of the other subprocess  702  described above. If the connection is not successful (step  760 ), the field unit  210  uses the directional antenna in an attempt to connect to the next highest ranked base station (step  755 ). Again, it should be understood that when attempting to connect to the next highest ranked base station, the directional antenna  400  is set to have a scan angle associated with that next highest ranked base station.  
     [0053]FIG. 8 is a flow diagram of a process  800  that performs a scan (steps  730  and  750 ) through use of the directional antenna  400 , as described in reference to FIG. 7. After the process  800  begins (step  802 ), the process  800  selects a next angle setting (step  803 ) and calculates a received power of a pilot signal or other predetermined signal associated with a given base station (step  805 ). The process  800  calculates a metric as a function of noise (e.g., E s /N o ) of a channel associated with the pilot signal (step  810 ). These three steps ( 803 ,  805 , and  810 ) are repeated until all angle settings have been measured (step  815 ).  
     [0054] Following the measurements, the process  800  selects and ranks angle settings of the directional antenna based on a combination of the received power and metric (step  820 ). The process  800  is then complete (step  825 ), and a table, database, or other reference to the rankings and angle settings may be output from the process  800 .  
     [0055] It should also be understood that this process may result in a single angle setting (i.e., the “best” angle setting) for use by the process  700  of FIG. 7, where the process  800 , in this alternative embodiment, is used on an as-needed basis.  
     [0056]FIG. 9A is a flow diagram of a pointing process used to set the direction of the antenna apparatus  400  based on a ranking process. The controller  350  uses the pointing process to determine optimum impedance settings of the selectable impedance components  411  through  414  during startup, i.e., when the AT  82  is initially establishing a communications link with the BSP  92  via the antenna apparatus  400 . During start-up (beginning in Step  903 ), the antenna apparatus  400  is placed in omni-mode (Step  906 ). The antenna apparatus  400  locks onto the “best” BSP  92  (Steps  909 - 921 ) and performs an initial pilot scan (Step  924 ).  
     [0057] The field unit  210  may include a sophisticated digital receiver that can provide output parameters such as E s /N o , Pilot Power, Total Received Power, RMS Delay Spread (if a so-called “rake receiver” is used to separate multipath), Forward Error Rate (FER), and other receiver signal metrics. Other technology capable of determining these signal metrics may alternatively be employed.  
     [0058] The antenna apparatus  400  is then put in directive mode, and the same parameters are recorded at each of the  1  through i&#39;th different pointing angles or modes (Step  927 ). It should again be understood that the principles of the present invention are based in part on the observation that the location of the BSP  92  in relation to any one field unit  210  (e.g., laptop  80 ) is approximately circumferential in nature. That is, if a circle is drawn around a field unit and different locations are assumed to have a minimum of one degree of granularity between any two locations, the BSP  92  can be located at any of a number of different pointing angles or modes. Assuming accuracy to ten degrees, for example, there are thirty-six different possible modes or setting combinations that exist for such an antenna apparatus  400 . Each phase setting combination can be thought of as a set of five impedance values, one for each selectable impedance component  410 - 414  electrically connected to respective passive antenna elements  401  through  405 .  
     [0059] Once this “database” is generated, each mode, including the omni-mode, is ranked from  1  through i&#39;th plus omni-mode using a ranking process (Step  933 ). The preferred angle or mode ranking process of choice may include using E s /N o  and Pilot Power, as shown below:  
       Rank  ( A   0 )= Es   0   /No   0   +PilotPwr   0    
       Rank  ( A   1 )= Es   1   /No   1   +PilotPwr   1    
       Rank  ( A   2 )= Es   2   /No   2   +PilotPwr   2    
     [0060] where:  
     [0061] E s /N o =energy per pilot symbol to total noise ratio in decibels (dB&#39;s);  
     [0062] PilotPwr=Received Pilot Power of Selected Base Station in decibels referenced to 1 milliwatt (dBm&#39;s); and  
     [0063] Rank(A i )=the ranking value for the i&#39;th mode or angle.  
     [0064] This metric is preferred because correlated power has a much stronger relationship to reverse link performance than signal-to-noise. For example:  
     Angle 6 : E   s   /N   o =8dB  PilotPwr=− 100dBm Ranking Value=−92  
     [0065] Angle 10 : E   s   l /N   o =6.5 dB  PilotPwr=− 92 dBm Ranking Value=−85.5  
     [0066] In general, if only E s /N o  is used, then Angle 6 is ranked higher than Angle 10 even though there is only a 1.5 dB difference in E s /N o . By using PilotPwr in the ranking, Angle 10 is ranked higher, which, in many cases, results in a more acceptable reverse link.  
     [0067] Although it may be suggested that, since power control is available, it does not matter if transmit power of the subscriber must be increased. This is true (i) if there is an infinite amount of transmit power in the subscriber unit, and (ii) if the additional power being transmitting does not contribute to same cell and other cell interference. Since this is not the case, it is better to try to balance the forward and reverse links as best as possible.  
     [0068] Because pilot symbols are used for the E s /N o  measurement metric in the angle ranking, antenna pointing decisions can be made before traffic channels are ever set-up. Additionally, since the pilot power is traditionally fixed, this gives a stable baseline that linearly degrades as interference and multi-path get worse.  
     [0069] The E s /N o  of the Pilot Signal is used as opposed to the E s /N o  of Traffic signals, since there are times when no Traffic data is being sent. Referring to the noise component of this metric, E s /N o , if the forward link is assumed to be interference limited, the biggest contributor to No is interference from adjacent cells and multi-path. By using Pilot E s /N o , which starts with a fixed ratio, any degradation in this ratio is expected to come from adjacent cell interference and multi-path.  
     [0070] Other factors that could be used in ranking the modes include Total Received Power, RMS Delay Spread, and FER, as mentioned above.  
     [0071] Returning attention to FIG. 9A, the processor  350  then provides and sets the optimal impedance for each selectable impedance component  411  through  414  using the highest ranking antenna mode first (Step  936 ). Next, a reverse link connection is initiated using the highest ranked antenna mode (Step  939 ). If a suitable connection cannot be made (Step  942 ), the processor  350  sets the next highest ranked candidate mode (Steps  945 - 948 ), and a reverse link connection is initiated using this mode. This process continues until a successful reverse link connection is achieved, the number of candidate modes to try is reached, or the omni mode is reached (Steps  942 - 954 ).  
     [0072] This process  900  can be used to point a directional antenna operating in virtually any environment but is particularly suited for use in cellular networks, Wireless Local Area Networks (WLANs), or other environments that are strongly influenced by interference/multi-path or operate using a different transmit (TX) and receive (RX) frequency.  
     [0073] An alternative selection process may be used to choose the “best”—base station as opposed to the best angle for an already-selected base station—to set the direction of the antenna apparatus  400  based on a ranking process. An example of this alternative process is shown in FIG. 9B. Similar to choosing a best angle setting following selection of the base station in omni mode as described in reference to FIG. 9A, setting the direction of the antenna apparatus  400  is accomplished by setting the impedance for each selectable impedance component  411  through  414 .  
     [0074] Referring to FIG. 9B, during start-up (beginning in Step  905 ), the antenna apparatus  400  is placed in directional-mode (Step  957 ), and the antenna apparatus  400  locks onto 1 of i&#39;th BSPs  92  and performs an initial pilot scan (Step  909 ).  
     [0075] The antenna apparatus  400  then records the same parameters at each of the 1 through i&#39;th different pointing BSPs (Steps  924 - 930 ).  
     [0076] Once this database is generated (Step  960 ), each BSP is ranked from 1 through i&#39;th using a ranking process (Step  963 ). The preferred “best” BSP ranking process of choice is using E s /N o  and Pilot Power, as shown below:  
       Rank  ( A   0 )= Es   o   No   0   +PilotPwr   0    
       Rank  ( A   1 )= Es   1   /No   1   +PilotPwr   1    
       Rank  ( A   i )= Es   i   /No   i   +PilotPwr   i    
     [0077] where:  
     [0078] E s /N o  =energy per pilot symbol to total noise ratio in decibels (dB&#39;s);  
     [0079] PilotPwr=Received Pilot Power of Selected Base Station in decibels referenced to 1 milliwatt (dBm&#39;s); and  
     [0080] Rank(A i )=the ranking value for the i&#39;th BSP.  
     [0081] Continuing to refer to FIG. 9B, the processor  350  then provides and sets the optimal impedance for each selectable impedance component  411  through  414  using the highest ranking BSP first (Step  966 ). Next, a reverse link connection is initiated using the highest ranked BSP (Steps  969 - 972  and  939 ). If a suitable connection cannot be made (Step  942 ), the processor  350  sets the antenna angle toward the next highest ranked candidate BSP (Steps  975 - 978 ), and a reverse link connection is initiated using this mode. This process continues until a successful reverse link connection is achieved or the number of candidate BSPs to try is reached (Steps  951 - 954 ).  
     [0082] This process can be used to point a directional antenna  400  operating in virtually any environment but is particularly suited for use in cellular networks or other environments that are strongly influenced by interference/multi-path and that operate using different transmit (TX) and receive (RX) frequencies.  
     [0083] The selection process described above may be improved or fine tuned by adding predetermined or adaptively learned information about the operating environment or directivity of the directive antenna  400 . This information is represented in the field unit  210 , or other system in which the present invention is employed, as weights.  
     [0084]FIG. 10 is a flow diagram of a process  1000  in which these weights are applied to the metrics related to noise and predetermined signal power learned through use of the scanning process  800 .  
     [0085] Referring to the process  1000 , the process  1000  begins (step  1005 ) and calculates the noise-related metric (e.g., E s /N o ) and pilot power metric using, for example, steps  805  and  810  discussed above in reference to FIG. 8 (step  1010 ). If weights are to be applied (step  1015 ), then the selected weights are determined in steps  1020  and  1025 .  
     [0086] If the weights are environmental in nature, the process  1000  calculates or receives the environmental weights (step  1020 ). If calculating the weights, the field unit  210  is operating in an autonomous mode (i.e., the field unit self-determines the environmental weights). If the field unit receives the environmental weights, the base station has provided these weights via wireless communication, and, thus, the field unit  210  has not acted autonomously.  
     [0087] If the weights to be applied are based on the directivity of the directional antenna (i.e., the weights are directional), the process  1000  may calculate, receive, or be preprogrammed with a Correlation Factor (CF) (step  1025 ). The correlation factor is a particular type of weighting and based on the antenna pattern. The correlation factor is discussed further below in reference to FIGS.  11 - 13 .  
     [0088] If no weights are to applied, the weightings are set to the value “1”. The process  1000  multiplies the weights by the respective metrics. For example, a first environmental weight and first directional weight may be multiplied by the metric that is a function of noise, and a second environmental weight and second directional weight may be multiplied by the metric related to pilot power (step  1030 ). When the process  1000  ends (step  1035 ), the weighted metrics may be stored in a table, database, or sent to the real-time running program on the field unit  210  for use in making an angle selection. The weighted metrics can then be used similar to the non-weighted metrics, as discussed above.  
     [0089] One way to establish the weights relative to the environment (i.e., environmental adjustment factors) for different areas is based on simulations of different statistically significant environments, such as urban, suburban, or rural. Other ways to establish these weights can be based on actual field measurements. Alternatively, these weights can be established in real-time based on an optimization routine using a kernel based on simulations or blind adaptive optimization.  
     [0090] An optimization routine can be set-up to optimize different metrics based on the needs of the specific network. For example, in dense urban areas, forward capacity, i.e., forward signal-to-noise ratio (SNR), may be considered a greater concern than range improvements, so the process can be set to converge on best SNR for each user. Likewise, in rural areas, coverage can be considered a greater concern, so received signal power or subscriber transmit power may be optimized.  
     [0091] One way to implement the adjustment factors is to preprogram values into each field unit  10 . These values may be based on geographic areas, i.e., planet earth, different continents, different countries, different regions within the different countries, and the user&#39;s home area network. These values allow for macro adjustments of the process based on the geographic area in which a user operates their field units. These values do not account for relocation of the user to a different geographic area or a major variation within the user&#39;s own geographic area. Therefore, there is a high probability the weights related to environment may not be correct for the user&#39;s field units if the user moves to a new geographic area or a major variation within the user&#39;s own geographic area.  
     [0092] A second way to implement the adjustment factors is to embed a predefined database in the field unit  210 . The predefined database may include different weights for a set of predefined environments, e.g., rural, suburban, urban, and metropolitan areas. When a user logs onto a particular network, the base station may notify the field unit of the type of environment in which the user is located. The field unit loads the predefined value associated with the environment from its internal database based on the information provided by the base station. This method does not easily allow for changes to the weighting factors for different environments, nor does it support real-time adjustments of the factors.  
     [0093] The preferred method uses specific weights for the smallest definable region. These weights may be dynamically downloaded to the user&#39;s field unit during login, or the weights can be continuously broadcast to the user&#39;s field unit. In a cellular network, each base station may contain its own set of weights that may be downloaded to each user over some control channel or broadcast over a broadcast channel. The network engineer who is managing a particular site can “tweak” these parameters to further optimize performance in a particular cell. The parameters the network engineer can “tweak” may be based on capacity, time of day, or a Link Quality Metric (LQM). Automatic tweaking of the weights may be accomplished using a network optimization tool, which monitors the overall system and network performance. The optimization tool collects link statistics and builds a database of the performance of users within the cell. The optimization tool inputs the statistics into a real-time modeling program and uses permutation techniques, for example, to try and solve for the optimum weights that maximize overall system performance.  
     [0094] The preferred angle or mode ranking algorithm of choice is using E s /N o  and Pilot Power, as shown below:  
       Rank  (A 0 )= RfAntEsNoWgt×Es   0   /No   0   +RfAntPilotWgt×PilotPwr   0    
       Rank  (A 1 )= RfAntEsNoWgt×Es   1   /No   1   +RfAntPilotWgt×PilotPwr   1    
       Rank  (A i )= RfAntEsNoWgt×Es   i   /No   i   +RfAntPilotWgt×PilotPwr   i    
     [0095] where:  
     [0096] E s /N o =energy per pilot symbol to total noise ratio in decibels (dB&#39;s);  
     [0097] PilotPwr=Received Pilot Power of Selected Base Station in decibels referenced to 1 milliwatt (dBm&#39;s);  
     [0098] Rant(A i )=the ranking value for the i&#39;th mode or angle;  
     [0099] RfAntEsNoWgt=the E s /N o  weight that is downloaded from the current Base Station, internal, or adaptively determined that defines how the E s /N o  should factor into the pointing decision for that base station environment; and  
     [0100] RfAntPilotWgt=the Pilot Power weight that is downloaded from the current Base Station, internal, or adaptively determined that defines how the Pilot Power should factor into the pointing decision for that base station environment.  
     [0101] The E s /N o  of the Pilot Signal is used as opposed the E s /N o  of Traffic signals for the same reason as discussed above, namely, the pointing direction decision preferably occurs during initial system access when no Traffic data is being sent. If the forward link is assumed to be interference limited, the biggest contributor to No is interference from adjacent cells and multi-path. By using Pilot E s /N o , one starts with a fixed ratio, and any degradation in this ratio comes from adjacent cell interference and multi-path.  
     [0102] Other factors that can be used in ranking the modes include Total Received Power, RMS Delay Spread, and FER, as mentioned above.  
     [0103] In addition to weights related to the operating environment that can be applied to the metrics to fine tune the pointing, weights related to the antenna directivity or beam pattern can also be applied to the metrics for fine tuning. These directional weights can be applied independent of or in addition to the environmental weights.  
     [0104] An example of a directional weight is an Antenna Pattern Correlation Factor (CF). The CF is a comparison between a free space antenna pattern of a directional antenna and any metric recorded as a function of the antenna pointing direction. The patterns can be, but are not limited to, expressions in continuous form or discrete measurements. The comparison can be performed by continuous or discrete convolution or by some other comparison technique, such as least-mean-square.  
     [0105] One type of comparison compares the free space pattern of the directional antenna  400  to pilot power. The comparison locates the center of mass of the pilot energy and forms a metric to describe the presence and severity of the multipath environment.  
     [0106]FIG. 11 illustrates a theoretical free space directional antenna pattern replicated ten times using ten different reference positions, Angle 1 through Angle 10. The free space reference pattern may be obtained by measuring the antenna in a nonreflecting environment. To quantify the multi-path environment, it is useful to use the free space antenna pattern because a determination must be made on how much the measured pattern (e.g., the pilot power) deviates from the free space pattern. The lower the value of the comparison (i.e., a smaller CF) between the measured pattern and the free space directional antenna pattern, the more severe the multi-path environment. Likewise, the higher the value of the comparison, the less severe the multi-path environment.  
     [0107]FIG. 12 illustrates a theoretical free space directional antenna and a theoretically measured pilot power pattern. As shown in FIG. 12, Angle 5 has the highest correlation between each of the ten free space antenna patterns and the measured pilot power pattern. Therefore, Angle 5 is selected as the optimum pointing angle. However, calculating the maximum CF further optimizes the pointing angle. The maximum CF can be calculated using the correlation value computed using Angle 5 and a complex pointing process. The CF is smaller in environments with greater multi-path angular spread and larger in environments with less multi-path angular spread. One method to calculate CF for each antenna position j is to use the following equation:  
       CF   j =1−( sum   i-32 1−&gt;A ( sqrt ( abs ( Diff   i,j )/ X )  
     [0108] where:  
     [0109] CF is the correlation factor;  
     [0110] “A” is the total number of angles measured;  
     [0111] “Diff” is the difference between the i&#39;th measured value and the j&#39;th antenna pattern; and  
     [0112] “X” is the maximum total difference that is obtained if a flat noise pattern is convolved with the actual free space antenna pattern.  
     [0113]FIG. 13 illustrates a process to compute the maximum CF using an actual measured free space antenna pattern and a measured pilot power pattern. The process may be described, in list format, as follows:  
     [0114] Outer Loop  
     [0115] 1. Normalize the peak of the measured pilot pattern to the peak of the free space antenna reference patterns;  
     [0116] 2. Select the first of the ten different free space antenna patterns;  
     [0117] Inner Loop  
     [0118] a. Convert the measured pilot power pattern and the recorded free space reference patterns to power in watts.  
     [0119] b. Calculate the difference between the free space reference pattern and the measured pilot pattern at the current angle (Diff).  
     [0120] c. Calculate the absolute value of the difference;  
     [0121] d. Calculate the square root of the difference;  
     [0122] e. Divide that difference by the maximum total difference of what is obtained if a flat noise pattern is convolved with the actual free space antenna pattern. For example, for the directional antenna  400 , the value is 7.6951;  
     [0123] f. Perform the Inner Loop b through e until D1 through D10 have been computed;  
     [0124] g. Sum the results of D1 through D10 and subtract this value from 1;  
     [0125] 3. Select the next free space antenna pattern and perform the Inner Loop again;  
     [0126] 4. Once all 10 free space reference patterns have a CF computed, the reference pattern with the largest value (between 0 and 1) is the direction of the center of mass of the pilot energy with a value of CF that is CFmax.  
     [0127] Once the database of modes (i.e., angles or base stations as discussed in referenced to FIG. 7) and CF max  is generated, each mode is ranked from 1 through i&#39;th using a weighted ranking process to obtain the optimum pointing angle. One example of a weighted ranking process is to weight the PilotPwr by the CF. Simulations and measurements have shown it is desirable to weight the received PilotPwr less as the multi-path environment gets worse because the PilotPwr in the Ranking equations is used to match the Forward and Reverse Links. It is difficult to find a predominant angle of arrival of the Base Station pilot as the multi-path environment gets worse. Hence, the contribution to the ranking by the PilotPwr is preferably reduced. The preferred angle or mode ranking process of choice is using E s /N o  and weighted Pilot Power, as shown below:  
       Rank  ( A   0 )= Es   0   /No   0   +CF   max   ×PilotPwr   0    
       Rank  ( A   1 )= Es   1   /No   1   +CF   max   ×PilotPwr   1    
       Rank  ( A   i )= Es   i   /No   i   +CF   max   PilotPwr   i    
     [0128] Where:  
     [0129] E s /N o =energy per pilot symbol to total noise ratio in decibels (dB&#39;s);  
     [0130] PilotPwr=Received Pilot Power of Selected Base Station in decibels referenced to 1 milliwatt (dBm&#39;s);  
     [0131] Rank(A i )=the ranking value for the i&#39;th mode or angle; and  
     [0132] Cf max =largest correlation factor.  
     [0133] In addition to applying the CF to the ranking process alone, the CF can be applied in combination with the environmental weights, as follows:  
       Rank ( A   0 )= RfAntEsNoWgt×Es   0   /No   0   +CF   max   RfAntPilotWgt×PilotPwr   0    
       Rank ( A   1 )= RfAntEsNoWgt×Es   1 /No 1   +CF   max   ×RfAntPilotWgt×PilotPwr   1    
       Rank ( A   i )= RfAntEsNoWgt×Es   i   /No   i   +CF   max   ×RfAntPilotWgt×PilotPwr   i    
     [0134] While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.