Patent Application
20080013462
Example embodiments of this invention provide the capability to manage the resources of an access medium. Disclosed example techniques provide an indication of whether an amount of access attempts corresponds to an overload condition on the access medium. Disclosed example techniques for handling such a situation provide for minimizing or eliminating the effects of possible overload, which provides the ability to improve overall system throughput.
In one example the network 22 comprises a wireless communication network that operates in a known manner. In such an example, the access terminals 26-34 comprise mobile stations such as cell phones, personal digital assistants or notebook computers, for example. The access medium for a wireless communication network comprises a communication channel, which is facilitated by a base station for example, that the access terminals can access in a known manner for initiating a call or flow. The schematic connections between the access terminals 26-34 in such an example comprise wireless communication links.
In another example, the network 22 is line based and operates in a known manner. In such an example, the access terminals may be computers or other devices associated with the network 22 that gain access to a server or communicate with each other by accessing the access medium 24, which comprises one or more lines (e.g., hardwired connections). The schematic connections between the access terminals 26-34 in one such example comprise hardwired communication links.
In some situations, the number of access attempts from access terminals will approach the capacity of the access medium 24. Under such situations, the access medium 24 may be considered to be overloaded because it cannot allow the access attempts to all get through on the first attempt. Under congested or overloaded conditions, the access attempts from two or more of the access terminals will collide on the access medium resulting in a failed attempt for each of the involved terminals. This is a known condition that occurs for known reasons.
The illustrated example provides the ability to recognize such a situation and to take corrective action to improve throughput and overall system performance.
The illustrated example includes three possible determinations at 44. One example includes selecting one of them for making the decision at 44. Another example includes a combination of two or all three of the possible determinations for making the decision at 44.
One example determination shown at 46 includes determining whether an average number of probes associated with successful access attempts indicates an amount of access attempts corresponding to a congested or overloaded access medium condition. As known, access messages often include a field in the header indicating the number of probes that message has been tried. Each access message typically is sent multiple times and each time corresponds to a probe. Therefore, the probe number indicates how many times a particular access message was tried before it was successful. Larger probe numbers correspond to higher attempt numbers. One example includes using this information as an indication that there is a correspondingly high rate of collisions on the access medium 24, which is causing the relatively high number of retransmissions (e.g., probes).
In one example, the network 22 includes a processor 47 that gathers and processes data regarding the number of probes associated with each successful access message. The average number of probes is compared to a selected threshold that is determined based upon characteristics of the particular network. When the average number of probes is above the threshold, the access medium 24 is congested or overloaded. Those skilled in the art who have the benefit of this description will be able to select an appropriate threshold and an appropriate number of received access messages or an appropriate sampling time for inclusion in a determination of the average number of probes to meet their particular needs.
In the illustrated example, an access medium occupancy measurement or determination is made at 48. In this example, the occupancy of the access channel is determined over a time interval of a selected duration. In one example, the occupancy is determined from the relationship: ρ=Nsiezures/CT, where T is the measurement interval, C is the capacity of the access medium in seizures per second (e.g., how many probes the access medium 24 can handle in a unit of time) and Nsiezures is the number of successful access attempts (e.g., captured probes) received in T.
In one example, for each detection time interval T, the value of ρ is compared to a selected threshold. If ρ exceeds the threshold, then the access medium 24 is considered overloaded. In one example, the threshold is selected to correspond to the access medium 24 being between approximately 70% and 80% occupied. The random nature of the access attempts from access terminals typically dictates that the total capacity of the access medium will never be reached. Given this description, those skilled in the art will be able to select an appropriate threshold.
Another determination is schematically shown at 60 in the example of
In wireless communication systems such as CDMA systems, the interference on the reverse link in closely related to the carried loading in the system. If the loading in the system is small while the total interference is high, for example, that provides an indication that there might be many access attempts that are not getting through. The high number of access attempts causes the high interference level. When the determined received signal strength has a relationship to the interference level that is outside of a selected range, the determination at 60 includes a conclusion that the access medium 24 is congested or overloaded. Given this description, those skilled in the art will realize what received power and interference levels for their particular situation will provide an indication of congestion or overload.
Another technique is included in the example of
One example condition that is likely to result in overload on an access medium is scheduled network maintenance or configuration. For example, system parameters and configurations will sometimes need updating. Such information is provided to all users through a broadcast message, for example. The corresponding changes will sometimes cause the users to send access attempts to request updating the user information, also. For example, in a wireless communication system, users may request a universal access terminal identification if the system changes its code for a particular network component. Such a situation has the potential to overload the access medium. In the event this happens abruptly, the access medium loading changes abruptly, also.
It is desirable to recognize the potential for such a situation and to predict the likelihood of corresponding overload. The illustrated example includes using information such as times associated with pre-scheduled maintenance or configuration operations for predicting when overload may occur.
Another example situation where there is a predictable, abrupt increase in access attempts is during an emergency situation when more users are likely to attempt to make a call than otherwise may happen. In many local emergency situations such as a natural disaster, for example, many users try to access the communication network 22 essentially at the same time. The loading on the access medium 24 at such times is much larger than in normal, everyday situations. One example includes an ability to trigger a recognition of the likelihood of overload whenever an emergency situation is detected. Given this description, those skilled in the art will be able to configure an appropriate portion of their particular network to accept suitable information indicating such a situation and to responsively provide an indication that overload control is desired to meet the needs of their particular situation.
In one example, whenever at least one of the determinations at 44 or the prediction at 62 indicates that the access medium is (at least expected to be) congested or overloaded, at least one technique is implemented at 64 for managing access attempts to stabilize the access channel by reducing or eliminating the congested or overloaded condition. Controlling overload or congestion at 64 in the illustrated example includes three techniques. Some examples include using one of the techniques while other examples include using a combination of two or all three of them.
One example technique is shown at 66 where access attempts are throttled to reduce the number of attempts for at least a selected amount of time. In one example, the network 22 directs at least some access terminals 26-34 to stop attempting to access the medium 24. The network 22 selects the users with lower access priority in one example. In another example, the users are randomly selected. This is accomplished in one example through a broadcast message from the network 22 that changes an access persistence parameter, which is used by an access terminal to control a probability that the terminal will send an access request. When the probability is zero, the access terminal will not send a request.
After an appropriate time the access terminal can increase the parameter above zero so that an attempt to initiate a new call or flow can be accomplished. In other words, the affected access terminals will not be effectively rendered unusable by having their access persistence parameter permanently set to zero.
In one example, the percentage of throttled users whose persistence parameter probability should be changed to zero is determined by the relationship: ρuser=(ρ−ρth)/ρ where ρ is the access medium occupancy and ρth is the access medium occupancy threshold.
Another technique is schematically shown at 68. This technique includes smoothing out a traffic burst on the access medium to reduce the loading. In this example, the network 22 sends a broadcast message with a smaller access persistence parameter so that each user will reduce its access attempt rate. The new access persistence parameter in one example is determined using the relationship αpersistence
The techniques shown at 66 and 68 may be implemented for a preselected time period or until a determination is made that there no longer is congestion or overload on the access medium 24. For example, the broadcast message indicating that the persistence parameter probability should be reduced may include a time during which the reduced probability should be used by an affected access terminal. In one example, at least some of the access terminals have an ability to automatically reset the persistence parameter to a default value after a selected time.
Another example technique is included at 70. With this technique, the access traffic loading is reduced by adjusting the access medium parameters (e.g., the access channel structure). In one example, each access attempt consists of a number of probe sequences, which each consist of a number of probes. Whenever overload is detected, the number of probe sequences, the number of probes in a sequence or both is selectively reduced to relieve the loading for stabilizing the access medium. This technique essentially changing at least one of the back off time, the number of probes or the number of probe sequences used by the access terminals.
By recognizing when a congestion or overload condition occurs on an access medium, the above example provides the ability to better manage the capacity of an access medium, which has the advantage of improving overall system throughput and performance in some examples.
The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims.
