Abstract:
Embodiments disclosed herein provide systems and methods for dynamically adjusting preambles for a random access channel. In a particular embodiment, a method provides, for a wireless access node having a random access channel, determining a demand for contention based preambles of the random access channel and a demand for contention free preambles of the random access channel. The method further provides determining a number of contention based preambles and a number of contention free preambles for the random access channel based on the demand for contention based preambles and the demand for contention free preambles. The method also provides allocating the number of contention based preambles and the number of contention free preambles to the random access channel.

Description:
TECHNICAL BACKGROUND 
     Some wireless communication network protocols employ a random access channel for wireless communication devices to use when initiating wireless communications with a wireless access node. A wireless device attempting to initiate communications with the access node requests a communication channel over the random access channel using one of a fixed number of preambles for communications on the random access channel. Of the fixed number of preambles, a portion of the preambles is allocated as contention based preambles and the remainder of the preambles are allocated as contention free preambles. 
     If a wireless device is originating communications on the access node, then the wireless device uses a contention based preamble, which the device selects at random, to communicate over the random access channel. As the preamble is contention based, it is possible that another wireless device will attempt to use the same preamble to initiate communications. Thus, the access node employs a contention resolution procedure during times when multiple devices use the same preamble. 
     Alternatively, if the communications originated on another access node and are handing off to the access node, then the wireless device is assigned a contention free preamble that only that particular wireless device is able to use on the random access channel for communicating at that time. Contention free preambles allow a wireless device that is handing off to initiate communications with the new access node without the risk of adverse effects caused by a preamble collision. 
     While the number of wireless devices needing either contention based or contention free preambles may change over time, the portions of the total number of preambles on the random access channel allocated as each preamble type remains constant. Thus, at times, the demand for one type of preamble may not be satisfied by the constant preamble allocation. 
     OVERVIEW 
     Embodiments disclosed herein provide systems and methods for dynamically adjusting preambles for a random access channel. In a particular embodiment, a method provides, for a wireless access node having a random access channel, determining a demand for contention based preambles of the random access channel and a demand for contention free preambles of the random access channel. The method further provides determining a number of contention based preambles and a number of contention free preambles for the random access channel based on the demand for contention based preambles and the demand for contention free preambles. The method also provides allocating the number of contention based preambles and the number of contention free preambles to the random access channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a wireless communication system for dynamically adjusting preambles for a random access channel. 
         FIG. 2  illustrates an operation of the wireless communication system for dynamically adjusting preambles for a random access channel. 
         FIG. 3  illustrates a wireless communication system for dynamically adjusting preambles for a random access channel. 
         FIG. 4  is a sequence diagram illustrating an operation of the wireless communication system for dynamically adjusting preambles for a random access channel. 
         FIG. 5  illustrates an operation of the wireless communication system for dynamically adjusting preambles for a random access channel. 
         FIG. 6  illustrates a communication control system for dynamically adjusting preambles for a random access channel. 
     
    
    
     DETAILED DESCRIPTION 
     The following description and associated figures teach the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects of the best mode may be simplified or omitted. The following claims specify the scope of the invention. Note that some aspects of the best mode may not fall within the scope of the invention as specified by the claims. Thus, those skilled in the art will appreciate variations from the best mode that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents. 
       FIG. 1  illustrates wireless communication system  100 . Wireless communication system  100  includes wireless communication device  101 , wireless access node  102 , and communication control system  103 . Wireless communication device  101  and wireless access node  102  communicate over wireless link  111 . Wireless access node  102  and communication control system  103  communicate over communication link  112 . 
     In operation, wireless access node  102  and control system  104  are part of a wireless communication network that provides communication services to wireless communication devices, such as wireless device  101 . While not shown, the wireless communication network may also include other access nodes and systems for providing the communication services. Access node  102  exchanges communications with wireless devices using a wireless protocol, such as Long Term Evolution (LTE), that uses a random access channel. 
     The random access channel is a shared channel (i.e. used, or capable of being used, by multiple wireless devices concurrently) that is used by wireless devices to initiate communications with access node  102 . The random access channel has a fixed number of preambles that can each be used by a respective wireless device. A number of these preambles are contention free preambles that are assigned for use by a single wireless device at any given time. In contrast, a number of the preambles are contention based preambles that can be used by any wireless device. If more than one device uses a single one of the contention based preambles concurrently, then access node  102  implements a procedure to resolve the contention of the multiple devices. 
     Contention free preambles are typically assigned to wireless devices that hand off from another access node to access node  102  while exchanging wireless communications. A contention free preamble aids the handover process by allowing the wireless device to initiate communications with access node  102  over the random access channel using the contention free preamble without the risk of a collision with another device using the same preamble. Contention based preambles are used by wireless devices not already exchanging communications with the wireless network. A device randomly selects one of the contention based preambles (since a specific preamble cannot be assigned to the device by virtue of the device not yet exchanging communications with the network) and uses that preamble in an attempt to establish communications with access node  102  over the random access channel. 
     The number of contention free and the number of contention based preambles out of the total number of available preambles are static. Therefore, if a number of wireless devices handing off to access node  102  is, or will be, greater than the number of contention free preambles available, then the number of contention free preambles is not increased to help accommodate the larger number of handing off devices. In a similar example, if a number of wireless devices attempting to initiate communications with access node  102  is, or will be, greater the number of contention based preambles, then the number of contention based preambles is not increased to help alleviate collisions on the existing contention based preambles. 
       FIG. 2  illustrates an operation of wireless communication system  100  to dynamically adjust preambles on a random access channel. For wireless access node  101  having a random access channel, control system  103  determines a demand for contention based preambles of the random access channel and a demand for contention free preambles of the random access channel (step  200 ). The demand for contention based and contention free preambles may be based on current activity of wireless devices or based on anticipated activity. 
     The demand for contention free preambles may be determined based on a number of wireless communication devices that are, or soon will be, in the process of handing off to wireless access node  102 . Each of those devices are, or soon will be, in need of a contention free preamble to initiate communications with access node  102  when handing off to access node  102  from another access node. Determining that a number of wireless devices will soon be handing off to wireless access node  102  may be based on mobility of wireless devices in access nodes neighboring access node  102 . For example, as devices enter a state of mobility, the chances that the devices will need to handoff between access nodes increases because a stationary device is not likely to handoff. The mobility state of a wireless device may depend upon device speed, direction, as well as other factors. 
     To determine anticipated activity, control system  103  may track activity of wireless devices over time and then use that activity information to determine expected device activity for a similar time period. For example, control system  103  from tracking the number of handoffs that occur at given times, control system  103  may determine that the demand for contention free preambles increases during rush hour on weekdays as wireless device users commute to and from work. Additional factors may also contribute to a determination of anticipated activity. For example, a large event may be scheduled during a time period for an area within the coverage area of access node  102 . Therefore, control system  103  may determine, based on information for the event (i.e. expected attendance), that the demand for contention based preambles will be greater due to an increased number of devices that may need to initiate communications with access node  102 . 
     Control system  103  then determines a number of contention based preambles and a number of contention free preambles for the random access channel based on the demand for contention based preambles and the demand for contention free preambles (step  202 ). In some embodiments, control system  103  will balance the number contention based preambles and the number of contention free preambles within the total number of preambles available on the random access channel. The balancing between the two types of preambles may be performed in proportion to the determined demands. For example control system  103  may determine the number of each type of preamble such that the ratio of contention based preambles to contention free preambles is equivalent to the ratio of the demand for contention based preambles and the demand for contention free preambles. 
     In some embodiments, control system  103  increases the number of contention free preambles if the demand for contention free preambles increases and increases the number of contention based preambles if the number of contention based preambles increase. These increases may be performed regardless of the demand for the other type of preamble. Alternatively, control system  103  may consider other factors when determining the number of each type of preamble. For example, contention free preambles may be considered higher priority so that communications already in progress do not drop when handing over to access node  102 . Thus, control system  103  will increase the number of contention free preambles even if increasing the number of contention free preambles would reduce the number of contention based preambles below demand. 
     Control system  103  then allocates the number of contention based preambles and the number of contention free preambles to the random access channel (step  204 ). Control system  103  may transfer a message to access node  102  instructing access node  102  to operate using determined numbers of each type of preamble. In some embodiments, control system  103  may further determine and specify to access node  102  which specific preambles of should be designated to each preamble type while, in other embodiments, access node  102  determines the specific preamble designations itself. 
     Other access nodes may also receive a notification so that those access node can assign contention free preambles of access node  102  to wireless devices that are handing off to access node  102 . Wireless device  101  and other wireless devices within the coverage area of access node  102  may also receive messages from access node  102  indicating which preambles are now designated contention based for use when the wireless devices initiate communications with access node  102 . 
     Referring back to  FIG. 1 , wireless communication device  101  comprises Radio Frequency (RF) communication circuitry and an antenna. The RF communication circuitry typically includes an amplifier, filter, modulator, and signal processing circuitry. Wireless communication device  101  may also include a user interface, memory device, software, processing circuitry, or some other communication components. Wireless communication device  101  may be a telephone, computer, e-book, mobile Internet appliance, wireless network interface card, media player, game console, or some other wireless communication apparatus—including combinations thereof. 
     Wireless access node  102  comprises RF communication circuitry and an antenna. The RF communication circuitry typically includes an amplifier, filter, RF modulator, and signal processing circuitry. Wireless access node  102  may also comprise a router, server, memory device, software, processing circuitry, cabling, power supply, network communication interface, structural support, or some other communication apparatus. Wireless access node  102  could be a base station, eNodeB, Internet access node, telephony service node, wireless data access point, or some other wireless communication system—including combinations thereof. 
     Communication control system  103  comprises a computer system and communication interface. Communication control system  103  may also include other components such as a router, server, data storage system, and power supply. Communication control system  103  may reside in a single device or may be distributed across multiple devices. Communication control system  103  is shown externally to wireless access node  102 , but system  103  could be integrated within the components of wireless access node  102  or within some other component of a wireless communication network. Communication control system  103  could be a mobile switching center, network gateway system, Internet access node, application server, service node, or some other communication system—including combinations thereof. 
     Wireless link  111  uses the air or space as the transport media. Wireless link  111  may use various protocols, such as Code Division Multiple Access (CDMA), Evolution Data Only (EVDO), Worldwide Interoperability for Microwave Access (WIMAX), Global System for Mobile Communication (GSM), Long Term Evolution (LTE), Wireless Fidelity (WIFI), High Speed Packet Access (HSPA), or some other wireless communication format. Communication link  112  uses metal, glass, air, space, or some other material as the transport media. Communication link  112  could use various communication protocols, such as Time Division Multiplex (TDM), Internet Protocol (IP), Ethernet, communication signaling, CDMA, EVDO, WIMAX, GSM, LTE, WIFI, HSPA, or some other communication format—including combinations thereof. Communication link  112  could be a direct link or may include intermediate networks, systems, or devices. 
       FIG. 3  illustrates wireless communication system  300 . Wireless communication system  300  includes wireless communication devices  301  and  302 , eNodeBs  303 - 306 , communication control system  307 , and LTE wireless network  308 . Wireless communication device  301  and eNodeB  304  communicate over wireless link  311 . Wireless communication device  302  and eNodeB  305  communicate over wireless link  312 . eNodeBs  303 - 306  and LTE wireless network  308  communicate over communication links  313 - 316 , respectively. LTE wireless network  308  and communication control system  307  communicate over communication link  117 . 
       FIG. 4  is a sequence diagram illustrating an operation of wireless communication system  400  to dynamically adjust preambles on a random access channel. In this embodiment, control system  307  is configured to allocate contention based and contention free preambles on each respective random access channel for eNodeBs  303 - 306 . The random access channel for each eNodeB includes 64 preambles for the purposes of this embodiment. Therefore, control system  307  allocates each of the 64 preambles to be either contention based or contention free. 
     In order to allocate the preambles, control system  307  receives mobility information from each of eNodeBs  303 - 306 . The mobility information may indicate to control system  307  whether wireless devices within the coverage areas of each base station are moving, how fast the devices are moving, directions in which the devices are moving, or other information related to the movement of wireless devices—including combinations thereof. Based on the mobility information, control system  307  is able to determine whether the wireless devices are moving and where those devices are moving. Wireless devices that are not moving are more likely to need contention based preambles to initiate communications with their respective eNodeBs. Alternatively, wireless devices that are moving are more likely to require contention free preambles on the eNodeB to which they are moving so that communications exchanged with those devices can handoff to that eNodeB. 
     In accordance with the mobility information, control system  307  determines a preamble allocation for each of eNodeBs  303 - 306 . For example, if the mobility information indicates that more contention free preambles are needed on eNodeB  304  than contention based preambles, then control system  307  allocates more of the 64 preambles of eNodeB  304  to be contention free preambles. Control system  304  then notifies eNodeB  304  of the determined allocation so that eNodeB  304  can implement its preambles in accordance with the allocation. In addition to notifying the other eNodeBs of their respective allocations, control system  307  may also indicate at least a portion of the allocation information for eNodeB  304  to the other eNodeBs so that the other eNodeBs can assign a contention free preamble to any wireless devices handing off to eNodeB  304 . 
     In an example of this embodiment, wireless device  301  is within the coverage area of eNodeB  304  and is thereby notified of the preambles that are allocated as contention based preambles in accordance with control system  307 . Thus, when wireless device  301  initiates a communication session with eNodeB  304 , wireless device  301  selects one of the preambles allocated as contention based to perform the initiation. Additionally, wireless device  302  is currently exchanging communications in a communication session with eNodeB  305  and is moving towards handing off with eNodeB  304 . Therefore, in preparation for the handoff and wireless device  302  needing to initiate communications with eNodeB  304  to continue the communication session, wireless device  302  is assigned one of the preambles allocated as contention free. Wireless device  302  then uses that contention free preamble to initiate and handoff communications for the communication session to eNodeB  304 . 
     In operation, control system  307  may continue to adjust the preamble allocations for each of eNodeBs  303 - 306  in order to account for current demand for each type of preamble. 
       FIG. 5  illustrates an operation of wireless communication system  300  to dynamically adjust preambles on a random access channel based on expected demand. Over time, control system  307  receives mobility information from eNodeBs  303 - 306  and determines demands for contention free and contention based preambles at the time the mobility information was collected (step  500 ). The demands are then stored in a storage system in correlation with the time the mobility information was collected (i.e. time of day, day, week, month, etc.) for later reference. In some embodiments, the mobility information itself may be stored in addition to the demands or alternatively to the demands so that the demands can be calculated at a later time. Control system  307  may also store additional information about the time period that may be useful when determining an expected demand (e.g. events, weather conditions, etc.). 
     At a later time, control system  307  accesses the storage system to determine a number of contention based preambles and a number of contention free preambles based on demands stored for one or more time periods corresponding to the later time (step  502 ). For example, the demands around noon on a Saturday for eNodeB  304  will likely be similar to demands around noon on Saturdays in the past. However, as mentioned above, if the storage system further stores additional information related to the time in which the mobility information was captured, then control system  307  may further consider demands during times having similar aspects in the additional information. In some embodiments, control system  307  may also consider demands for non-corresponding time periods having similar additional information. 
     After determining the number of contention based preambles and the number of contention free preambles based on the stored demands, control system  307  allocates the respective preamble numbers to the random access channel for each of eNodeBs  303 - 306  (step  504 ). In some embodiments, control system  307  may subsequently adjust the preamble allocations to better account for actual mobility conditions experienced for wireless devices communicating with eNodeBs  303 - 306 . 
       FIG. 6  illustrates communication control system  600 . Communication control system  600  is an example of communication control system  103 , although control system  103  may use alternative configurations. Communication control system  600  comprises communication interface  601 , user interface  602 , and processing system  603 . Processing system  603  is linked to communication interface  601  and user interface  602 . Processing system  603  includes processing circuitry  605  and memory device  606  that stores operating software  607 . 
     Communication interface  601  comprises components that communicate over communication links, such as network cards, ports, RF transceivers, processing circuitry and software, or some other communication devices. Communication interface  601  may be configured to communicate over metallic, wireless, or optical links. Communication interface  601  may be configured to use TDM, IP, Ethernet, optical networking, wireless protocols, communication signaling, or some other communication format—including combinations thereof. 
     User interface  602  comprises components that interact with a user. User interface  602  may include a keyboard, display screen, mouse, touch pad, or some other user input/output apparatus. User interface  602  may be omitted in some examples. 
     Processing circuitry  605  comprises microprocessor and other circuitry that retrieves and executes operating software  607  from memory device  606 . Memory device  606  comprises a non-transitory storage medium, such as a disk drive, flash drive, data storage circuitry, or some other memory apparatus. Operating software  607  comprises computer programs, firmware, or some other form of machine-readable processing instructions. Operating software  607  includes demand determination module  608  and allocation module  609 . Operating software  607  may further include an operating system, utilities, drivers, network interfaces, applications, or some other type of software. When executed by circuitry  605 , operating software  607  directs processing system  603  to operate communication control system  600  as described herein. 
     In particular, demand determination module  608  directs processing system  603  to, for a wireless access node having a random access channel, determine a demand for contention based preambles of the random access channel and a demand for contention free preambles of the random access channel. Allocation module  609  directs processing system  603  to determine a number of contention based preambles and a number of contention free preambles for the random access channel based on the demand for contention based preambles and the demand for contention free preambles. Allocation module  609  further directs processing system  603  to allocate the number of contention based preambles and the number of contention free preambles to the random access channel. 
     The above description and associated figures teach the best mode of the invention. The following claims specify the scope of the invention. Note that some aspects of the best mode may not fall within the scope of the invention as specified by the claims. Those skilled in the art will appreciate that the features described above can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described above, but only by the following claims and their equivalents.