Abstract:
This invention provides a dynamic frequency hopping system that utilizes information from multiple base stations. The system assigns frequency hopping patterns based on current interference and traffic environments to avoid interference thus gaining the benefits of interference averaging and interference avoidance. The system imposes less stringent measurement requirements on terminals (wireless mobile devices) because many measurement requirements are replaced by generating estimates based on measurement data received from other base stations within a base station neighborhood. The system may continuously verify that the frequency hopping patterns assigned to the links of the system optimizes system performance. The system compares system performance of possible frequency hopping patterns against currently assigned frequency hopping pattern to optimize system performance. When a request for a link is received, a similar process as above is performed where the request is granted/denied/delayed based on system optimization requirements. In this way, the frequency hopping patterns of the links of the system may be assigned so that an optimum system performance may be obtained.

Description:
This Application is a Provisional claiming benefits under U.S. patent Ser. No. 60/165,913 filed on Nov. 17, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to dynamic frequency hopping. 
     2. Description of Related Art 
     Frequency hopping patterns are used in wireless communications to take advantage of interference averaging effects obtained by changing frequencies when transmitting a block of data. Conventionally, frequency hopping patterns have been selected in a random matter. However, with increasing popularity of wireless systems such as cellular phones or personal digital assistance (PDAs), greater efficiency in resource utilization is required than provided by random frequency hopping. Thus, new technology is needed to increase resource utilization efficiency. 
     SUMMARY OF THE INVENTION 
     This invention provides a dynamic frequency hopping system that utilizes information from multiple base stations to optimize an estimated performance of each individual link, of all links supported by a single base station or of all currently active links supported by the complete communication system. The system assigns frequency hopping patterns based on current interference and traffic environments to avoid interference thus gaining the benefits of interference averaging and interference avoidance. 
     The system imposes less stringent measurement requirements on terminals (wireless mobile devices) because many measurement requirements are replaced by generating estimates based on measurement data received from other base stations within a base station neighborhood. A base station neighborhood of a first base station is a group of second base stations that may be affected by first links serviced by the first base station. The base station neighborhood may be defined by a link neighborhood. A link neighborhood of a link includes all other links whose interference to the link exceeds an interference threshold. Thus, any of the first links that is included in link neighborhoods of second links serviced by the second base stations may interfere with the second links. Therefore, the second base stations are included in the base station neighborhood of the first base station. 
     The dynamic frequency hopping system may continuously verify that the frequency hopping patterns assigned to the links of the system optimizes an estimated system performance. Each currently assigned frequency hopping pattern is compared against all other possible frequency hopping patterns that may be assigned to a particular link. A possible frequency hopping pattern that corresponds to a maximum possible estimated system performance is compared against a current estimated system performance corresponding to the current frequency hopping pattern. If the current estimated system performance is less than the maximum possible estimated system performance, then the frequency hopping pattern of the particular link is changed to the possible frequency hopping pattern to improve system performance. 
     When a request for a link is received by the dynamic frequency hopping system, a similar process as above is performed where the request is granted allocation of system resources and assigned a frequency hopping pattern if the total estimated system performance exceeds a performance threshold. If the performance threshold is not exceeded, then the request for a link may be either delayed or denied. In this way, the frequency hopping patterns of all the links of the system may be assigned so that an optimum system performance may be obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is described with reference to the following figures, wherein like numerals identify like elements, and wherein: 
     FIG. 1 is an exemplary block diagram of a dynamic frequency hopping system; 
     FIG. 2 is an exemplary diagram of a frequency hopping pattern; 
     FIG. 3 is an exemplary diagram illustrating a base station in connection with a terminal; 
     FIG. 4 is an exemplary diagram of available frequencies; 
     FIG. 5 is an exemplary block diagram of a dynamic frequency hopping system having a centralized dynamic hopping device; 
     FIG. 6 is an exemplary block diagram of a dynamic frequency hopping management device; 
     FIG. 7 is a flowchart of an exemplary process of the dynamic frequency hopping management device for assigning frequency hopping patterns based on signal-interference-plus-noise-ratio; 
     FIG. 8 is a flowchart for an exemplary process for generating a list of available frequencies; 
     FIG. 9 is a flowchart for an exemplary process for assigning frequencies to a new frequency hopping pattern; 
     FIG. 10 is a flowchart for en exemplary process for verifying optimum system performance; and 
     FIG. 11 is a flowchart for an exemplary process for selecting possible frequency hopping patterns. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a dynamic frequency hopping system  100  that makes frequency hopping pattern assignments based on information that is detected by terminals throughout the system, information derived from the detected information and/or information resulting from decisions made throughout the system. The dynamic frequency hopping system  100  includes a network  102  and base stations  110 ,  112  and  114 . The base stations  110 - 114  are coupled to the network  102  which provides inter-base station communication for allocating wireless network resources for frequency hopping. 
     The dynamic frequency hopping system  100  also includes terminals  134 - 136  wirelessly communicating with the base stations  110 - 1   14  via links  104 - 108 , respectively. Associated with each of the links  104 - 108  is a link neighborhood  116 - 120 . FIG. 1 shows the link neighborhoods  116 - 120  as contours which may be defined based on parameters such as geographic areas, interference and/or noise thresholds, N largest interference/noise sources, etc. As an example, FIG. 1 shows link neighborhood  118  of link  106  including link  104  while excluding link  108 . 
     Each of the terminals  134 - 136  may detect or measure information such as path gain between each of the terminals  134 - 136  and the base stations  110 - 114  and transmit the detected information to a select one of the base stations  110 - 114 . The terminals  134 - 136  may select a respective base station  110 - 114  based on path gain information. For example, the terminal  134  may detect signal strength from control signals being transmitted by each of the base stations  110 - 114  and select the base station  112  because the path gain with the base station  112  is the largest. Then the terminal  134  transmits all the detected information or information derived from the detected information to the base station  112 . The control signal transmitted by the base station  110 - 112  may include a base station identification, an identification of a channel on which a terminal  134 - 136  may transmit the detected information, etc. as is well known in the art. 
     When a request for a link  106  for the terminal  134  is received (e.g., the terminal  134  makes a call or the terminal  134  receives a call), the base station  112  may allocate wireless communication resources to the link  106  based on resource allocation techniques disclosed in U.S patent applications entitled “Allocation of Wireless Network Resources” filed by Chawala et al., on Dec. 3, 1999, having Ser. No. 09/453,565; and “Wireless Resource allocation” filed by Chawala et al., on Dec. 3, 1999, having Ser. No. 09/453,566, for example. Both of the above-two U.S. applications are hereby incorporated by reference. Instead of a single frequency or channel as discussed in the above applications, a frequency hopping pattern is allocated that optimizes the system. The dynamic frequency hopping system  100  assigns the frequency hopping pattern to the terminal  134  based on the techniques applied to channels in the above applications. 
     FIG. 2 shows an example of a frequency hopping pattern  200  that may be assigned to the terminal  134 . The frequency hopping pattern  200  includes a pattern of eight different frequencies  202 - 216  where each frequency is used for transmission for a duration (or dwell) of 10 milliseconds (ms). The sequence of frequencies is the hopping pattern that is assigned and transmitted to the terminal  134 . The terminal  134  communicates with the base station  112  by transmitting information in the frequency sequence and duration of each frequency as specified by the frequency hopping pattern. Thus, the terminal  134  may begin by transmitting information using frequency  202  for a duration of 10 ms and then transmits information using frequency  204  for the next 10 ms, and so on. When transmission using the frequency  216  is completed, the terminal  134  repeats the frequency hopping pattern until either the communication is completed or until the frequency hopping pattern is changed by the base station  112 . 
     While the exemplary frequency hopping pattern  200  shows eight frequencies of 10 milsecs per frequency and a frequency range varying between 810 MHz to 880 MHz, the particulars of a frequency hopping pattern may be changed and adapted based on specific implementation details. For example, the frequency range of the hopping pattern may be regulated by various government entities and the duration of each of the frequencies in the frequency hopping pattern may be determined based on wireless transmission conditions such as noise environment, congestion, etc. This invention provides a dynamic frequency hopping system  100  that selects a frequency hopping pattern which optimizes system performance. 
     Conventional frequency hopping patterns provides benefits of interference averaging achieved by channel coding over multiple hops. Thus, if one or a few hops experience strong interference, the transmitted information can still be reliably recovered. Therefore, interference averaging provides robustness to sudden change in one or more interferers as well as robustness to measurement and estimation errors and fading of the channel. This invention further extends the benefits of frequency hopping by ensuring that the frequency hops experience weaker interference by avoiding strong interferers. 
     It is assumed that all the links  104 - 108  are synchronized (i.e., frequency and frame) so that all the links  104 - 108  hop from one frequency to another frequency at substantially the same time. Thus, interference among the links  104 - 108  may be determined without considerations of the percentage of time that interference may occur. Additionally, it is assumed that interference between links occurs when the links  104 - 108  are communicating within a same frequency neighborhood (i.e., those frequencies whose cross frequency interference exceeds a threshold set as a system parameter). For a frequency neighborhood of 1, interference occurs when more than one link  104 - 108  communicate using the same frequency. However, adjacent frequencies may also interfere. Thus, depending on specific circumstances, frequency neighborhoods of more than one may be considered. In the following discussion, frequency neighborhood of 1 is assumed. Thus, different frequencies in a frequency hopping pattern are assumed not to interfere with each other. However, the following discussion may be extended to frequency neighborhoods of greater than 1. 
     As is discussed below, the signal-interference-plus-noise-ratio (SINR) of a link may be defined in terms of power and path gains of all currently active links for a frequency neighborhood. Thus, to avoid any interference, all of the frequencies assigned to frequency hopping patterns for currently active links may not be assigned to another link for the same dwell period. However, if two links are separated in such a way that the path gains between a receiver of one link and a transmitter of another link is below a path gain threshold, then the two links may be considered non-interfering and frequencies of the same frequency neighborhood may be assigned to the two links for the same dwell period. 
     Based on the above, a link neighborhood may be associated with each link where a first link (a transmitter of the link, for example) may be included in a link neighborhood of a second link (a receiver of the second link, for example) if the path gain between the respective transmitter and receiver of the two links is less than a path gain threshold. 
     Based on the above, the link neighborhood  118  of FIG. 1 includes the link  104  if the link  104  is a downlink from the base station  110  to the terminal  134  and the link neighborhood  116  includes the link  106  if the link  106  is uplink from the terminal  134  to the base station  112 . 
     The size of the link neighborhoods  116 - 120  may be adjusted depending on a particular cost/performance levels desired. The link neighborhoods  116 - 120  may be selected based on a trade off between optimizing performance of the wireless communication system  100  and resources of the network  102  (i.e., costs) that are required to support that performance. In the ideal case, the link neighborhoods  116 - 120  may be defined to include all links  104 - 108  of the wireless communication system  100 . If such a definition is assumed, then path gain and other information from all the base stations  110 - 114  of the dynamic frequency hopping system  100  must be included to determine whether to allocate resources such as to assign a frequency hopping pattern to a requested link. For this case, all the base stations  110 - 114  are required to constantly communicate with every other base station in the dynamic frequency hopping system  100  to achieve optimum system performance. The cost to support such a communication may be very high. 
     The cost may be reduced while controlling the impact on system performance by limiting the size of the link neighborhoods  116 - 120  based on magnitudes of interference that are expected to be received, for example. The link neighborhood of link r may be defined as follows: 
     1) sort all links of a wireless communication system in a descending order based on a magnitude of interference that may be expected from a link q on link r; then 
     2) select the first K r  links q in the sorted order to be the link neighborhood for link r. 
     In this way, the size of a link neighborhood K r  may be balanced against an efficiency of the frequency assignments by accounting for interference that may be sustained by other links  104 - 108  within the link neighborhood of a limited size. Thus, cost and performance are optimized by balancing the magnitude of K r  against the cost required to provide inter-base station communications over the network  102 . 
     FIG. 3 shows a functional block diagram of the terminal  134  and the base station  112  as an example to discuss the dynamic frequency hopping pattern assignment process. The terminal  134  detects channel quality for all the base stations  110 - 114  from which the terminal  134  can receive control signals as shown in functional block  302 . The detected information is transmitted wirelessly to the base station  112  which is servicing the terminal  134 . The base station  112  collects the detected information from the terminal  134  and all other terminals that are serviced by the base station  112  as shown in functional block  306 . The detected information that is collected by the base station  112  is stored in a database  308  as well as transmitted to other base stations  110 ,  114  via the network  102 . The database  308  also stores detected information received from other base stations  110 , 114  so that the database  308  has a “local” copy of all the detected information throughout the base station neighborhood. 
     The base station neighborhood of a base station  110 - 114  may be defined in terms of link neighborhoods of links  104 - 106  supported by the base stations  110 - 114 . For example, a base station neighborhood of the base station  112  may include all those base stations  110 ,  114  supporting links  104 - 108  that may receive interference from links  104 - 108  supported by the base station  112 . 
     For example, FIG. 1 shows that the link  106  is serviced by the base station  112 , and the link  104  is serviced by the base station  110 . The link  104  has a link neighborhood  116  that includes the link  106 . Thus, the base station neighborhood of base station  112  includes the base station  110 . The base station  114  may also be included in the base station neighborhood of the base station  112  if there was another link that is serviced by the base station  112  and that is included in the link neighborhood  120  of the link  108 . Thus, the base station neighborhood for a selected base station  110 - 114  includes all those base stations  110 - 114  that support links  104 - 108  having link neighborhoods that include a link serviced by the selected base station. The database  308  includes all the detected information that are collected by the base stations  110 - 114  that are within the base station neighborhood of the base station  112 . 
     The base station  112  also includes a frequency hopping pattern database  312 . The database  312  receives frequency hopping patterns from all the base stations  110 - 114  within the base station neighborhood of the base station  112  as well as the frequency hopping patterns assigned by the base station  112 . Thus, the database  312  includes the frequency hopping patterns of the links  104 ,  108  serviced by all the base stations  110 ,  114  within the base station neighborhood of the base station  112 . 
     The base station  112  includes a dynamic frequency hopping management device  310  that processes the information of the system  100  stored in the database  308  and the frequency hopping patterns in the database  312  to generate new frequency hopping patterns for the links  106  supported by the base station  112 . The base station  112  wirelessly transmits new frequency hopping patterns to the terminal  134 . The terminal  134  receives the new frequency hopping pattern form the base station  112  as shown in block  304  and applies the new frequency hopping pattern for further communications. 
     The frequency hopping pattern assignment process may be performed in three alternative ways as described below. 
     Independent Assignment 
     Each of the base stations  110 - 114  may independently assign frequency hopping patterns without any coordination among the base station  110 - 114  except for exchanging information such as detected information and frequency hopping pattern assignments, of all the base station  110 - 114 . The independent assignment process may be performed based on a performance criteria such as signal-interference-to-noise-ratio (SINR), optimum estimated performance or optimum estimated gain as described below. 
     The SINR is used as a criterion for frequency hopping assignment decisions in the discussed below as an example. However, one or more other link quality parameters such as block error rate, frame error rate, bit error rate measure, etc. may also be used as criteria for the frequency hopping assignment decisions without departing from the spirit of the invention. 
     The SINR of a link i for a particular frequency may be defined by equation (1) below:                SINR   i     =         P   i          G   ii             ∑     j   ≠   i              P   j          G   ji         +     n   i                 (   1   )                                
     where P i  is the power transmitted over the link i, G ii  is a path gain over the link i for a receiver of the link i, P j  is the power transmitted over one or more links j, G ji  is the path gain from transmitters of the links j to the receiver of link i, and n i  is the receiver noise of the receiver. Thus, the numerator of equation (1) represents the power received by the receiver when receiving signals over the link i. The denominator represents the sum of all the interfering power received by the receiver of link i from all the transmitters of other links j transmitting in the particular frequency (or frequency neighborhood) for the link i plus the noise power at the receiver of link i. P i  and G ii  are available locally at a base station  110 - 1   14  that is servicing the link i and P j  and G ji  may be obtained (via the network  102 ) from one or more base stations  110 ,  114  servicing links j, if necessary. 
     The dynamic frequency hopping management device  310  may first determine the SINR for each of the frequencies assigned to frequency hopping patterns of currently active links serviced by the base station  112 . Then, the dynamic frequency hopping management device  310  compares each of the SINRs against a SINR threshold. A number of frequencies in a frequency hopping pattern that is less than the SINR threshold is determined. When this number falls below a marking threshold, then the dynamic frequency hopping management device  310  marks the corresponding link for assignment of a new frequency hopping pattern. 
     For each of the marked links, the dynamic frequency hopping management device  310  generates available frequencies that may be assigned to the frequency hopping patterns of the marked links. As shown in FIG. 4, the available frequencies  320  for a marked link includes a first block  322  of unassigned frequencies. A second block  324  of currently assigned frequencies whose SINR is below the SINR threshold is also included because the SINR for a frequency may change when assigned to a different link due to different geographical conditions, for example. Thus, while the SINR of a frequency for one link may be below the SINR threshold, the SINR for another link may exceed the SINR threshold. A third block  326  of frequencies assigned to currently active links whose link neighborhood does not include the marked link may also be included. 
     The third block  326  is generated for each of the marked links by verifying whether the marked link is within the link neighborhood of any currently active link. If the marked link is not in the link neighborhood of a currently active link, then all the frequencies in the frequency hopping pattern of the currently active link are included in the available frequency list for the marked link. This process is performed for all the currently active links to generate the third block  326  of available frequencies. 
     The dynamic frequency hopping management device  310  may assign the frequencies to each of the marked links based on assignment rules such as: 
     1) Randomly select frequencies that have associated SINRs that exceed an assignment threshold. Assign the selected frequencies to replace those frequencies that have SINRs that is below the SINR threshold; 
     2) Select the frequencies that have the highest SINRs of the available frequency list and assign the selected frequencies as replacement frequencies. The dynamic frequency hopping management device  310  may rank all the frequencies in the available frequencies  320  based on communication qualities that may be obtained if each of the available frequencies is assigned to the marked link as part of a new frequency hopping pattern. Then, the frequencies corresponding to the highest ranked SINRs are assigned as either new or replacement frequencies; and 
     3) Make tentative frequency assignments for all the marked links from respective lists of available frequencies. Assign as replacement frequencies the tentative assignment for all the marked links that results in an optimum estimated performance for all the links serviced by the base station  110 - 114 . 
     Assignment guidelines 1 and 2 treat each link  106  separately from other links  106 . However, some of the frequencies of the available frequencies for each of the marked links may occur in the available frequency list of other marked links serviced by the same base station  112  (e.g., the unassigned frequencies of block  322 ). Thus, the available frequencies may be generated when needed so that each of the available frequencies takes into consideration frequency assignments that have already been made. 
     The assignment guideline  3  may consider all possible frequency assignments in terms of optimum estimated link performance for all the links serviced by the base station  112  independent of whether a link is marked. In actual implementation, links may be marked and only marked links may be considered to reduce base station processing loads. Optimum estimated link performance may include frequency assignments that optimizes an estimated signal quality for a link  106 , maximize a number of terminals  134 - 136  that may be serviced by the base station  112  or other performance characteristics that may be desired. For example, the dynamic frequency hopping management device  310  may not necessarily assign frequencies having the highest estimated performance for a selected link because the same available frequency may have highest SINR in more than one of the links. Thus, the dynamic frequency hopping management device  310  may consider spreading the highest SINR frequencies among all the links so that an overall optimum estimated performance for all of the active links may be obtained. 
     Optimum estimated performance corresponding to the available frequencies for each of the links may be based on any number of communication criteria. For example, if throughput is selected as a communication criterion, then the dynamic frequency hopping management device  310  generates an estimated throughput for each of the available frequencies for each of the links. 
     Estimated throughput T i   s  for link i at frequency s using mode m i  may be defined by equation (2) below. 
       T   s   i   =R   m     i    (1 −BLER   m      i   ( SINR   i ))  (2) 
     where m i  is a transmission mode for link i, R m     i    is a radio interface rate for link i transmitting using mode m i , BLER m      i    is a block error rate for the mode m i , and SINR i  is the SINR for a receiver of link i. While equation (2) defines the throughput as a function of the SINR, other link quality parameters may also be used to define the throughput such as frame error rate and bit error rate measure. 
     The transmission mode m i  is assigned to a link i for optimal transmission based on the transmission environment such as interference conditions. For example, different transmission modes such as QAM (Quadrature Amplitude Modulation), nPSK (n order phase shift keying), different types of coding (e.g., half rate coding), etc., have different transmission performance advantages depending on the transmission environment. 
     Based on the throughput generated using equation 2 above, the dynamic frequency hopping management device  310  may assign frequencies to optimize a total base station throughput parameter for the base station  112 . The total estimated throughput for a frequency neighborhood q, T q , is a sum of the estimated throughputs of all links actively supporting communications using the frequency q and may be defined by equation (3) below.                T   q     =       ∑     i   ∈     all                   links      in                   q              T   i   q               (   3   )                                
     The dynamic frequency hopping management device  310  assigns frequencies to the links so that T q  is maximized, for example. Alternatively, the dynamic frequency hopping management device  310  may assign any frequency combination that results in T q  exceeding a threshold. In this way, the dynamic frequency hopping management device  310  may avoid generating all possible T q s and may assign a first set of frequencies for which T q  exceeds the threshold. 
     The dynamic frequency hopping management device  310  may also make frequency assignments based on a link quality parameter improvement. For example, the dynamic frequency hopping management device  310  may make frequency hopping pattern assignments based on a difference between an original base station link estimated performance before the frequency hopping patterns are changed and a maximum new base station&#39;s estimated link performance after the frequency hopping patterns are changed. The total estimated throughput for the marked links may be generated for the originally assigned frequencies and new estimated throughputs frequency hopping patterns may be generated for each new possible frequency assignment. If the largest new estimated throughput of all the possible frequency assignments does not exceed the original estimated throughput by a gain threshold, then the original frequencies may be retained or the link may be assigned a mode zero to temporarily stop transmission until a later time when better interference and/or noise conditions are encountered. If the threshold value is set to a positive value, then the above procedure may not change a frequency pattern unless a throughput improvement is obtained. 
     Token Passing Assignment 
     Token passing assignment accounts for possible adverse interaction of frequency hopping pattern assignments between multiple base stations  110 - 114 . This technique provides a token passing procedure where only the base station  110 - 114  that possesses a token, for example, may assign new frequency hopping patterns to terminals  134 - 136  serviced by the base station  110 - 114 . For example, the base station  110 - 114  may be configured in a ring order much like a token ring network. A token may be initiated at any one of the base stations  110 - 114  and the base station  110 - 114  that has the token may assign new frequency hopping patterns. When the base station  110 - 114  has completed the link frequency hopping pattern assignments or after a set period of time, the token may be passed on to a next base station  110 - 114  based on the ring order. In this way, at any one time, only one base station  110 - 114  is assigning new frequency hopping patterns to its terminals  134 ,  136 . 
     The token passing procedure may also be controlled by a centralized token unit (not shown) where, a token is passed to a base station  110 - 114  by the centralized token unit via the network  102 . When the frequency hopping pattern assignments are completed or after the set period of time, the token maybe sent to a next base station  110 - 114 . The centralized token unit may easily change the sequence of base station frequency hopping pattern updates based on system wide conditions. Also, if necessary, selected base stations  110 - 114  may receive tokens more often than other base stations  110 - 114 . 
     The dynamic frequency hopping management device  310  may make total estimated system performance optimizations under the token assignment alternative because all the other base stations that the frequency hopping pattern assignments remain static while the base station  110 - 114  that possesses the token is assigning its new frequency hopping patterns. For example, if estimated system throughput is used as a performance parameter that is optimized, the dynamic frequency hopping management device  310  may generate an estimated system throughput parameter using equation 3 with the exception that the summation is taken over all the links in the complete system instead of only the links for a particular base station  110 - 114 . The frequency hopping patterns assigned to all the actively communicating links for the base station  112  that correspond to an estimated system throughput that exceeds a system throughput threshold may be assigned to optimize the estimated system performance. Alternatively, the dynamic frequency hopping management device  310  may assign a new frequency hopping pattern for all the links supported by the base station  112  that provide an estimated system throughput that exceeds a current estimated system throughput by a performance gain threshold. 
     Centralized Assignment 
     In the centralized assignment technique, the dynamic frequency hopping management device  310  may be a separate unit (or a specifically assigned base station  110 - 114 , for example) that interfaces with all the base stations  110 - 114  through the network  102 . As shown in FIG. 5, a dynamic frequency hopping system  101  includes a dynamic frequency hopping management device  340  that is connected to the network  102  and a database  342  coupled to the dynamic frequency hopping management device  340 . The dynamic frequency hopping management device  340  receives information (detected or generated) as well as the frequency hopping patterns from all the base stations  110 - 114 . The dynamic frequency hopping management device  340  provides for optimum estimated system performance by reviewing each of the frequency hopping patterns to verify whether a different frequency hopping pattern may be assigned to improve system performance. 
     For example, the dynamic frequency hopping management device  340  may generate estimated throughput for a current frequency hopping pattern assignment for all currently active links and also possible estimated throughputs for new potential frequency hopping patterns for the currently active links. The dynamic frequency hopping management device  340  may permute the frequency patterns through possible frequency patterns and select potential frequency patterns that provide an optimum possible estimated throughput. For example, if a possible estimated throughput exceeds the original estimated throughput by a threshold value, then the dynamic frequency hopping management device  340  may change the frequency pattern assignments to new frequency hopping patterns that corresponds to the optimum estimated throughput. In this way, the dynamic frequency hopping system  101  is constantly maintained at an optimum estimated system performance level. 
     The dynamic frequency hopping management device  340  may also determine optimum estimated performance based on the estimated system performance damage concept disclosed in U.S. Patent application Ser. No. 09/453,566 entitled “Wireless Network Resource Allocation” filed on December 3, which is herein incorporated by reference. A new frequency hopping pattern may be assigned for a particular link if the maximum estimated system gain that corresponds to a new frequency hopping pattern exceeds a gain threshold for the current frequency hopping pattern assignment. 
     While the above discussion addresses changing a frequency hopping pattern of a currently active link, the dynamic frequency hopping management device  310 ,  340  also assigns new frequency hopping patterns for a link request. The link request may be received from a terminal  134 - 136  when placing a call or initiating a data transfer, for example; when a call is received for a terminal  134 - 136 ; or when a data packet is being forwarded en route to its destination. 
     When a request is received for a new link, the dynamic frequency hopping management device  310 ,  340  may identify a list of available frequencies corresponding to blocks  322  and  326  as shown in FIG. 4, for example. Block  324  is not applicable because a new link has not yet been assigned a frequency hopping pattern. The dynamic frequency hopping management device  310 ,  340  may assign a new frequency hopping pattern using any of the techniques discussed above, i.e., random assignment of frequencies whose SINR exceed the assignment threshold, assignment of frequencies having highest SINRs, or assigning frequencies that provides for optimum base station estimated performance or estimated system performance. 
     Example Block Diagram and Processes of the Dynamic Frequency Hopping Management Device 
     FIG. 6 shows an exemplary block diagram for the dynamic frequency hopping management device  310 ,  340 . The dynamic frequency hopping management device  310 ,  340  may include a controller  402 , a memory  404 , a wireless interface  406 , a network interface  408  and a database interface  410 . The above components are coupled together via signal bus  412 . While the exemplary block diagram shown in FIG. 6 is illustrated in a bus architecture, any other types of architecture as dictated by implementation details may be used as is well known to one of ordinary skill in the art. The functions performed by the dynamic frequency hopping management device  310 ,  340  may be performed by application specific integrated circuits (ASICs), PLA, PLDs or a program executing in a general purpose or special purpose processor. 
     The dynamic frequency hopping management device  310 ,  340  receives detected information and other communication parameters such as frequency hopping pattern assignments, SINRs, etc. from the base stations  110 - 114  through the network interface  408 . The dynamic frequency hopping management device  310 ,  340  may receive detected information from terminals  134 - 136  directly, if necessary, via the wireless interface  406 . The received information are stored in the database  342  via the database interface  410 . The controller  402  controls the dynamic frequency hopping management device processes by performing the required functions using the memory  404  and processing the data that are stored in the database  342 . New frequency patterns may be communicated to the terminals  134 - 136  by sending the new frequency patterns to the respective base stations  110 - 114  via the network interface  408  or directly to the terminals  134 - 136  via the wireless interface  406 . If the dynamic frequency hopping management device  310 ,  340  is incorporated in the base stations  110 - 114 , the frequency hopping patterns are transmitted to the terminals  134 - 136  via the wireless interface  406  and communicated to all other base stations  110 - 114  via the network interface  408 . The functions performed by the dynamic frequency hopping management device  310 ,  340  are described in conjunction with flowcharts shown in the following FIGURES. 
     FIG. 7 shows a flowchart for an exemplary process of the dynamic frequency hopping management device  310 ,  340  for frequency assignment rules 1 and 2. In step  1000 , the controller  402  determines whether it is time to verify the frequency hopping pattern assignments. If it is time, the controller  402  goes to step  1002 ; otherwise, the controller  402  returns to step  1000 . In step  1002 , the controller  402  determines whether all the SINRs are available via either the database interface  410  or in the memory  404 . If available, the controller  402  goes to step  1006 ; otherwise, the controller  402  goes to step  1004 . In step  1004 , the controller  402  generates the SINRs that are needed and goes to step  1006 . 
     In step  1006 , the controller  402  marks those links whose frequency hopping patterns include frequencies that have corresponding SINRs which are below the SINR threshold and goes to step  1008 . In step  1008 , the controller  402  generates lists of available channels for all the marked links and goes to step  1010 . In step  1010 , the controller  402  assigns new frequency hopping patterns to all the marked links and goes to step  1012 . In step  1012 , the controller  402  sends the new frequency assignments to the terminals  134 - 136  via the wireless interface  406  (also via a base station  110 - 114  if the dynamic frequency hopping management device is the centralized unit) and goes to step  1014 . In step  1014 , the controller  402  determines whether a system off condition has been received. If received, the controller  402  goes to step  1016  and ends the process; otherwise, the controller  402  returns to step  1000  and continues the process. 
     FIG. 8 shows a flowchart of a subroutine that expands step  1008  of FIG. 7 in greater detail. In step  2000 , the controller  402  selects a marked link and goes to step  2002 . In step  2002 , the controller  402  adds unassigned frequencies to a list of available frequencies and goes to step  2004 . The list of available frequencies may be stored in the memory  404 , for example. In step  2004 , the controller  402  adds all the frequencies that have SINRs which are below the SINR threshold to the list of available frequencies and goes to step  2006 . 
     In step  2006 , the controller  402  selects a next remaining frequency. The remaining frequencies are those frequencies that are assigned to frequency hopping patterns of currently active links. Then the controller  402  goes to step  2008 . In step  2008 , the controller  402  determines whether the selected marked link is in a link neighborhood of the link that is associated with the remaining frequency. If associated, the controller  402  goes to step  2012 ; otherwise, the controller  402  goes to step  2010 . In step  2012 , the controller  402  determines whether any frequencies still remain. If frequencies still remain, the controller  402  returns to step  2006 ; otherwise, the controller  402  goes to step  2014 . In step  2010 , the controller  402  adds the selected remaining frequency to the list of available frequencies and goes to step  2012 . In step  2014 , the controller  402  determines whether there are more marked links. If there are more marked links, the controller  402  returns to step  2000 ; otherwise, the controller  402  goes to step  2018  and ends the process. 
     FIG. 9 shows a flowchart of a subroutine that expands step  1010  of FIG. 7 in greater detail for guideline 1 using an assignment threshold. In step  3000 , the controller  402  selects a marked link and goes to step  3002 . In step  3002 , the controller  402  selects a next frequency from the list of available frequencies corresponding to the selected marked link and goes to step  3004 . In step  3004 , the controller  402  determines whether the SINR corresponding to the selected frequency is greater than the assignment threshold. If greater, the controller  402  goes to step  3006 ; otherwise, the controller  402  returns to step  3002  and selects a next frequency. 
     In step  3006 , the controller  402  assigns the selected frequency to the frequency hopping pattern of the marked link then goes to step  3008 . In step  3008 , the controller  402  determines whether more frequencies are to be assigned to the marked link. If more frequencies are to be assigned, the controller  402  returns to step  3002 ; otherwise, the controller  402  goes to step  3010 . In step  3010 , the controller  402  determines whether there are more marked links to assign frequencies. If there are more marked links, the controller  402  returns to step  3000  and selects another marked link; otherwise, the controller  402  goes to step  3012  and ends the process. 
     The process for guideline 2 is similar to the assignment process discussed above with FIG.  9 . The difference is in step  3002 . Instead of selecting a next frequency from the list of available frequencies, the controller  402  ranks all of the available frequencies based on the magnitude of the SINR associated with each of the frequencies. Instead of step  3004 , the controller  402  selects a frequency corresponding to a next highest SINR. All subsequent steps  3006 - 3012  are identical to those shown in FIG.  9 . 
     FIG. 10 shows an exemplary flowchart for a process of the dynamic frequency hopping management device  310 ,  340  that assigns frequency hopping patterns to optimize an estimated system performance. In step  4000 , the controller  402  collects information from other base stations  110 ,  114  and from links serviced by the base station  112 , for example, and goes to step  4002 . In step  4002 , the controller  402  selects a next link to verify estimated system performance in relation to the assigned frequency hopping pattern for the link and goes to step  4004 . In step  4004 , the controller  402  generates three estimated throughput values (estimated throughput values being used as a measure of estimated system performance ) T ORG , T 0  and T NEW . T ORG  is the estimated system throughput for the currently assigned frequency hopping pattern for the selected link. T 0  is the estimated system throughput if the currently selected link is not permitted to transmit data (assign a transmission mode of 0); and T NEW  is the maximum estimated system throughput for all possible frequency hopping patterns that may be assigned to the selected link. 
     As discussed earlier, a list of available frequencies may be generated for the selected link where the list of available frequencies may include the unassigned frequencies corresponding to block  322  of FIG.  4  and frequencies of currently assigned active links having link neighborhoods that do not include the selected link corresponding to block  326  of FIG.  4 . The controller  402  tests every combination of the available frequencies to form possible frequency hopping patterns for the selected link and selects a possible frequency hopping pattern that corresponds to a maximum estimated system throughput T NEW . Then the controller goes to step  4006 . 
     In step  4006 , the controller  402  determines whether T 0  or T NEW  exceeds T ORG  by a gain threshold. If exceeded, the controller  402  goes to step  4008 ; otherwise, the controller  402  goes to step  4010 . In step  4008 , the controller  402  either assigns transmission mode 0 to the selected link or assigns the frequency hopping pattern corresponding to T NEW  to the selected link and goes to step  4010 . In step  4010 , the controller  402  determines whether a system off condition is detected. If detected, the controller  402  goes to step  4014  and ends the process; otherwise, the controller  402  returns to step  4002  and continues the verification process. 
     FIG. 11 shows a flowchart for a subroutine that expands step  4006  of FIG. 10 for generating T NEW  in greater detail. In step  5000 , the controller  402  sets the maximum estimated throughput T NEW  to an initial value and goes to step  5002 . In step  5002 , the controller  402  selects a next possible frequency hopping pattern. The possible frequency hopping patterns are possible combinations of available frequencies that may be assigned to the selected link. Then the controller  402  goes to step  5004 . In step  5004 , the controller  402  generates an estimated system throughput T. The estimated system throughput may be the sum of the estimated throughputs of each currently active link generated using equation 2 above where the estimated throughput for each of the frequencies for a frequency hopping pattern is summed together for a currently active link. Then the controller  402  goes to step  5006 . In step  5006 , the controller  402  determines whether the estimated system throughput T is greater than the maximum estimated system throughput T NEW . If T is greater than T NEW , the controller  402  goes to step  5008 ; otherwise, the controller  402  goes to step  5010 . 
     In step  5008 , the controller  402  sets T NEW  to T and goes to step  5010 . In step  5010 , the controller  402  determines whether more frequency hopping patterns remain. If more possible frequency hopping patterns remain, the controller  402  returns to step  5002 ; otherwise, the controller  402  goes to step  5012  and returns to the next processing step of FIG.  10 . 
     The estimated system throughput T may also be generated by using the nominal throughput and throughput damage techniques described in the wireless network resource allocation application, Ser.No. 09/453,566 mentioned above. Also, other system parameters other than system throughput may be used as an optimizing parameter such as a maximum number of terminals to be served by the base station or maintaining specific qualities of service. 
     The above-described processes in connection with FIGS. 10 and 11 may be applied to a single base station  110 - 114  to optimize total estimated performance of the links serviced by the base station  110 - 114  or on a system wide basis to optimize total estimated system performance. In addition, the processes described in FIGS. 7-11 may be applied to determine whether a request for a link should be allocated system resources and assign a frequency hopping pattern or the request denied because a desired system performance cannot be obtained. 
     Other Alternatives and Modifications 
     While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. For example, while the dynamic frequency hopping system  100  is discussed in terms of assigning frequencies to new frequency hopping patterns, the process is equally applicable to assigning different time division multiplexing (TDM) time slots or combinations of time slots and/or frequencies when the new frequency/slot hopping patterns are assigned. If TDM is used and the original frequency hopping pattern/slot assignment is: slot s o   1 -frequency f o   1 , slot s o   2 -frequency f o   2 , . . . , slot s o n-frequency f o n, then new frequency hopping pattern/slot assignment may be: slot s n   1 -frequency f n   1 , slot s n   2 -frequency f n   2 , . . . , slot s n n-frequency f n n. To obtain benefits of frequency diversity, f o   1 -f o n should be different frequencies and f n   1 -f n n should be different frequencies. The system performance may be generated for each available slot and the patterns of slot and frequency pairs that optimizes the system may be selected as the new patterns. Accordingly, preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.