Allocating root sequences to access nodes

In systems and methods of allocating root sequences to access nodes, a first coverage radius and a first neighbor list of a first access node are determined, wherein the first neighbor list comprises second access nodes which are each a neighbor access node of the first access node. A second coverage radius and a second neighbor list of each of the second access nodes is then determined. An access node comprising a largest coverage radius from among the first access node and the second access nodes is selected. A number of root sequences required for the selected access node is calculated based on the coverage radius of the selected access node, and root sequences are assigned to the selected access node according to the number of root sequences required.

TECHNICAL BACKGROUND

To initiate the establishment of a communication link with an access node, a wireless device may perform an initial synchronization process and a random access procedure. To perform the random access procedure, the wireless device typically selects a random access (RACH) preamble, and the wireless device can use the selected RACH preamble to transmit an initial access request to the access node. The randomly selected preamble can distinguish the wireless device's initial access request from other similar requests from other wireless devices. Access node preambles can be determined based on a unique sequence such as a root sequence. The same root sequence is typically not assigned to more than one access node in proximity to one other access nodes, to mitigate confusion among initial access requests received by the access nodes.

Preambles for each access node can then be obtained based on, for example, a cyclic shift of the assigned root sequence. The cyclic shift value can depend on the size of the coverage area of each access node, as well as other factors such as delay spread factors. In many cases, the larger the coverage area of the access node, the larger the cyclic shift which is required. Because root sequences cannot be assigned to more than one access node in relative proximity to other access nodes, root sequence assignment is an important consideration in network configuration.

Overview

In operation, a first coverage radius of a first access node is determined, as well as a first neighbor list of the first access node. The first neighbor list comprises second access nodes which are each a neighbor access node of the first access node. A second coverage radius and a second neighbor list of each of the second access nodes is determined. An access node comprising a largest coverage radius from among the first access node and the second access nodes is selected. A number of root sequences required for the selected access node is calculated based on the coverage radius of the selected access node, and root sequences are assigned to the selected access node according to the number of root sequences required.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary communication system100to allocate root sequences to access nodes in a wireless communication system comprising wireless device102, access node104, access node106, and communication network108. Examples of wireless device102can comprise a cell phone, a smart phone, a computing platform such as a laptop, palmtop, or tablet, a personal digital assistant, or an internet access device, including combinations thereof. Wireless device102can communicate with access node104over communication link110.

Access node104and access node106are each a network node capable of providing wireless communications to wireless device102, and can be, for example, a base transceiver station, a radio base station, an eNodeB device, or an enhanced eNodeB device. Access node104is in communication with communication network108over communication link112, and access node106is in communication with communication network108over communication link114. In an embodiment, access nodes104and106can be located in proximity to each other, and each access node can be a neighbor access node of the other.

Communication links110,112and114can be wired or wireless communication links. Wired communication links can comprise, for example, twisted pair cable, coaxial cable or fiber optic cable, or combinations thereof. Wireless communication links can comprise a radio frequency, microwave, infrared, or other similar signal, and can use a suitable communication protocol, for example, Global System for Mobile telecommunications (GSM), Code Division Multiple Access (CDMA), Worldwide Interoperability for Microwave Access (WiMAX), or Long Term Evolution (LTE), or combinations thereof. Other wireless protocols can also be used.

Other network elements may be present in communication system100to facilitate wireless communication but are omitted for clarity, such as base stations, base station controllers, gateways, mobile switching centers, dispatch application processors, and location registers such as a home location register or visitor location register. Furthermore, other network elements may be present to facilitate communication between access node104, access node106and communication network108which are omitted for clarity, including additional processing nodes, routers, gateways, and physical and/or wireless data links for carrying data among the various network elements.

Access node preambles can be determined based on a unique sequence such as a root sequence. To mitigate confusion among initial access requests received by access nodes, typically a unique root sequence is assigned to access nodes in proximity to one another. Preambles for each access node can then be obtained based on, for example, a cyclic shift of the assigned root sequence. The cyclic shift value can depend on the size of the coverage area of each access node, as well as other factors such as delay spread factors. In many cases, the larger the coverage area of the access node, the larger the cyclic shift which is required. Accordingly, an access node with a relatively large coverage area may require more than one root sequence to generate the requisite number of preambles for the access node. On the other hand, an access node with a relatively small coverage areas may use a smaller cyclic shift, and may therefore require only one root sequence to generate the requisite number of preambles for the access node. Because root sequences cannot be assigned to more than one access node in relative proximity to other access nodes, root sequence assignment is an important consideration in network configuration.

Configuring root sequences for access nodes based on an assumed fixed coverage radius, such as an average coverage radius of access nodes in a market or a geographic area, limits the number of available root sequences for assignment to the access nodes. When the number of root sequences is limited, the number of available RACH preambles available for initial network access can be limited, and network performance can be degraded. For example, call setup requests from wireless device can be delayed when insufficient RACH preambles are available. Similarly, the transmission of data from wireless devices to access nodes can be delayed when an uplink transmission is resumed from a suspended state, due to a lack of available preambles. In addition, the rate of call setup success and handover success can also be degraded.

In operation, to allocate root sequences to access nodes in communication system100, a first coverage radius of first access node104is determined and a first neighbor list of first access node104is also determined. The first neighbor list comprises second access nodes, for example, access node106, which are each a neighbor access node of first access node104. A second coverage radius and a second neighbor list of each of the second access nodes is then determined. For example a second coverage radius and a second neighbor list of access node106can be determined. Next, an access node comprising a largest coverage radius from among the first access node and the second access nodes is selected. A number of root sequences required for the selected access node is calculated based on the coverage radius of the selected access node, and root sequences are assigned to the selected access node according to the number of root sequences required.

In an embodiment, another access node comprising a next-largest coverage radius from is selected among the first access node and the second access nodes. For example, access node106may comprise the next-largest coverage radius after access node104. A second number of root sequences required for the selected another access node is calculated based on the coverage radius of the selected another access node, and root sequences are assigned to the selected another access node according to the second number of root sequences required. In an embodiment, the root sequences assigned to the selected another access node are different than the root sequences assigned to the selected access node.

FIG. 2illustrates an exemplary method of allocating root sequences to access nodes in a wireless communication system. In operation202, a first coverage radius of a first access node and a first neighbor list of the first access node are determined. The first neighbor list comprises second access nodes which are each a neighbor access node of the first access node. For example, a first coverage radius of access node104can be determined. The coverage radius can comprise a distance from the access node in which at least one signal level transmitted by access node104which is detectable at or above a signal level threshold. The coverage radius can be determined for access node104or for a subset of a coverage area of access node104, such as a sector of the access node.

In addition, a first neighbor list of access node104can be determined. The first neighbor list can comprise one or more access nodes in proximity to access node104, such as access node106. The first neighbor list can comprise access nodes comprising a coverage radius bordering or overlapping with the coverage radius of access node104.

Next, a second coverage radius and a second neighbor list of each of the second access nodes is determined (operation204). For example, a second coverage radius of access node106, and a second neighbor list of access node106, can be determined. The second coverage radius can comprise a radius in which at least one signal level transmitted by access node106which is detectable at or above a signal level threshold, and can be determined for access node106or for a subset of a coverage area of access node106, such as a sector of the access node. The second neighbor list can comprise one or more access nodes in proximity to access node106, which can comprise access nodes comprising a coverage radius bordering or overlapping with the coverage radius of access node106. While the second neighbor list can comprise first access node104, the second neighbor list will typically comprise at least one additional access node which is not a neighbor of access node104.

In operation206, an access node comprising a largest coverage radius from among the first access node and the second access nodes is selected. For example, access node104, comprising a larger coverage radius than access node106or any other neighbor access node of access node104, can be selected. An access node with a relatively large coverage area may require more than one root sequence to generate the requisite number of preambles for the access node. In an embodiment, 64 preambles can be generated for an access node, though the number of preambles required can be determined according to network access technology, communication protocols used in the communication system, available communication resources in wireless and wired communication links, and the like. On the other hand, an access node with a relatively small coverage areas may use a smaller cyclic shift, and may therefore require only one root sequence to generate the requisite number of preambles for the access node.

A number of root sequences required for the selected access node is calculated based on the coverage radius of the selected access node (operation208). For example, when access node104is selected, based on the first coverage radius, a number of root sequences can be calculated. Then, root sequences are assigned to the selected access node according to the number of root sequences required (operation210). Preambles for each access node can be obtained based on, for example, a cyclic shift of the assigned root sequence. The larger the cyclic shift, the larger the number of root sequences required by an access node. In operation, assigned root sequences are substantially consecutive, in part to enable wireless devices (e.g., wireless device102) to determine the root sequences assigned to an access node, and to determine the available RACH preambles for the wireless device to initiate communication with the access node.

FIG. 3illustrates another exemplary communication system300to allocate root sequences to access nodes in a wireless communication system comprising access nodes302,304,306,308,310,312, and314, communication network316, and processing node318. Access nodes302-314are each a network node capable of providing wireless communications to a wireless device (such as wireless device102), and can be, for example, a base transceiver station, a radio base station, an eNodeB device, or an enhanced eNodeB device. Access nodes302,304,306,308,310,312, and314are in communication with communication network316over communication links320,322,324,326,328,330and332, respectively. In an embodiment, access nodes304and306can comprise neighbor access nodes to access node302. Similarly, access nodes302and308can comprise neighbor access nodes to access node304; access nodes312and304can comprise neighbor access nodes to access node308; access nodes302and310can comprise neighbor access nodes to access node306; and access nodes306and314can comprise neighbor access nodes to access node310.

Processing node318can comprise a processor and associated circuitry to allocate root sequences to access nodes in a communication system300. Processing node318can retrieve and execute software from storage, which can include a disk drive, flash drive, memory circuitry, or some other memory device, and which can be local or remotely accessible. The software comprises computer programs, firmware, or some other form of machine-readable instructions, and may include an operating system, utilities, drivers, network interfaces, applications, or some other type of software, including combinations thereof. Processing node318can receive instructions and other input at a user interface. Examples of processing node318can include a standalone computing device, a computer system, or a network component, such as a mobile switching center (MSC), a dispatch call controller (DCC), a mobility management entity (MME), an access service network gateway (ASN-GW), a packet data network gateway (P-GW), a serving gateway (S-GW), a mobile switching controller (MSC), a packet data serving node (PDSN), call processing equipment, a home agent, a radio node controller (RNC), a subscriber profile system (SPS), authentication, authorization, and accounting (AAA) equipment, and a network gateway, or another similar network node, including combinations thereof. Processing node318is in communication with communication network316over communication link334.

Communication links320-334can be wired or wireless communication links. Wired communication links can comprise, for example, twisted pair cable, coaxial cable or fiber optic cable, or combinations thereof. Wireless communication links can comprise a radio frequency, microwave, infrared, or other similar signal, and can use a suitable communication protocol, for example, Global System for Mobile telecommunications (GSM), Code Division Multiple Access (CDMA), Worldwide Interoperability for Microwave Access (WiMAX), or Long Term Evolution (LTE), or combinations thereof. Other wireless protocols can also be used.

Other network elements may be present in communication system300to facilitate wireless communication but are omitted for clarity, such as base stations, base station controllers, gateways, mobile switching centers, dispatch application processors, and location registers such as a home location register or visitor location register. Furthermore, other network elements may be present to facilitate communication between and among access nodes302-314, communication network316, and processing node318, which are omitted for clarity, including additional processing nodes, routers, gateways, and physical and/or wireless data links for carrying data among the various network elements.

FIG. 4illustrates another exemplary method of allocating root sequences to access nodes in a wireless communication system. In operation402, a first coverage radius of a first access node and a first neighbor list are determined. The first neighbor list comprises second access nodes which are each a neighbor access node of the first access node. For example, a first coverage radius of access node302can be determined. The coverage radius can comprise a radius in which at least one signal level transmitted by access node302which is detectable at or above a signal level threshold. The coverage radius can be determined for access node302or for a subset of a coverage area of access node302, such as a sector of the access node.

In addition, a first neighbor list of access node302can be determined. The first neighbor list can comprise one or more access nodes in proximity to access node302, such as access nodes304and306. The first neighbor list can comprise access nodes comprising a coverage radius bordering or overlapping with the coverage radius of access node302. The first coverage radius and the first neighbor list can be determined by processing node318, or by another network element of communication system300. In an embodiment, processing node318can query access node302for the first neighbor list and the first coverage radius. Alternatively, or additionally, processing node318can receive information from each of access nodes302-314and can determine the first coverage radius and the first neighbor list based on the received information.

Next, a second coverage radius and a second neighbor list of each of the second access nodes is determined (operation404). For example, a second coverage radius of each of access nodes304and306, and a second neighbor list of each of access nodes304and306, can be determined. The second coverage radius can comprise a radius in which at least one signal level transmitted by access nodes304and306which is detectable at or above a signal level threshold, and can be determined for access nodes304and306or for a subset of a coverage area of access nodes304and306, such as a sector of an access node. The second neighbor list can comprise one or more access nodes in proximity to access nodes304and306, which can comprise access nodes comprising a coverage radius bordering or overlapping with the coverage radius of access nodes304and306. For example, a second neighbor list for access node304can comprise access nodes308and302, and a second neighbor list for access node306can comprise access node310and access node302. Access nodes308and310are not neighbors of access node302, each having access nodes304and306, respectively, interposed between access node302and access nodes308and310. Thus, while the second neighbor list can comprise first access node302, the second neighbor list will typically comprise at least one additional access node which is not a neighbor of access node304.

In operation406, an access node comprising a largest coverage radius from among the first access node and the second access nodes is selected. For example, access node302, comprising a larger coverage radius than access nodes304and306or any other neighbor access node of access node104, can be selected. An access node with a relatively large coverage area may require more than one root sequence to generate the requisite number of preambles for the access node. In an embodiment, 64 preambles can be generated for an access node, though the number of preambles required can be determined according to network access technology, communication protocols used in the communication system, available communication resources in wireless and wired communication links, and the like. On the other hand, an access node with a relatively small coverage areas may use a smaller cyclic shift, and may therefore require only one root sequence to generate the requisite number of preambles for the access node.

A cyclic shift is calculated for the selected access node, and a number of root sequences required for the selected access node is calculated based on the coverage radius and the cyclic shift of the selected access node (operation408). For example, when access node302is selected, based on the first coverage radius, a cyclic shift can be calculated for access node302. The larger the cyclic shift, the larger the number of root sequences required by an access node. Then, a number of root sequences can be calculated.

In an embodiment, the cyclic shift can be calculated based on a round trip delay and a delay spread associated with an access node. The round trip delay can comprise a time required for a signal to travel from an access node to a wireless device, and to be returned from the wireless device back to the access node. The delay spread can comprise a measure of multipath delay from an access node to a wireless device. In an embodiment, the delay spread can comprise a time difference between an arrival of a first multipath component and a second multipath component of a signal transmitted from the access node to the wireless device.

In operation410, root sequences are assigned to the selected access node according to the number of root sequences required. Preambles for each access node can be obtained based on, for example, a cyclic shift of the assigned root sequence. In operation, assigned root sequences are substantially consecutive, in part to enable wireless devices (e.g., wireless device102) to determine the root sequences assigned to an access node, and to determine the available RACH preambles for the wireless device to initiate communication with the access node. The number of assigned root sequences can comprise a length of a root sequence divided by the cyclic shift value. The length of the root sequence can be determined by an operator of communication network300, or it can be determined according to a communication protocol used in communication system300.

In operation412, another access node is selected comprising a next-largest coverage radius from among the first access node and the second access nodes. For example, access node304can comprise the next-largest coverage radius of the group of access nodes302-314, after access node302, so access node304can be selected next. A cyclic shift and a number of root sequences required for the next selected access node is calculated based on the coverage radius of the selected access node (operation414). For example, when access node302is selected, based on the first coverage radius, a number of root sequences can be calculated. Then, root sequences are assigned to the selected access node according to the number of root sequences required (operation416). Preambles for each access node can be obtained based on, for example, a cyclic shift of the assigned root sequence. The larger the cyclic shift, the larger the number of root sequences required by an access node.

In operation, assigned root sequences are substantially consecutive, in part to enable wireless devices (e.g., wireless device102) to determine the root sequences assigned to an access node, and to determine the available RACH preambles for the wireless device to initiate communication with the access node. Typically a unique root sequence is assigned to access nodes in proximity to one another, to mitigate potential confusion among access nodes when a wireless device sends a request to initiate communication with an access node. Thus, in operation, the root sequences assigned to the selected next-largest access node are different than the root sequences assigned to the selected access node. In an embodiment, a root sequence assigned to a first access node can be re-assigned to a second access node when the second access node does not include the first access node in its neighbor list. In operation, greater distance between access nodes can be used to mitigate possible confusion caused by re-use of root sequences, such as requiring that a root sequence is only re-assigned to a second access node which is three tiers away from the first access node (i.e., a neighbor of a neighbor of a neighbor of the first access node). For example, a root sequence assigned to access node302could be re-assigned to access node312or314, but not to access nodes304,306,308or310.

When root sequences are assigned to the first and second access nodes, the root sequences are transmitted to the respective access nodes (operation418). The root sequences can be transmitted via communication network316to each of the recipient access nodes and stored at each of the access nodes. In an embodiment, the root sequences themselves can be transmitted to the access nodes. Additionally, or alternatively, an index or another indicator of the root sequences, such as a root sequence indicator, can be transmitted to each access node to indicate the assigned root sequences. The root sequence index can then be used by each access node to determine the specific root sequences assigned.

In operation420, at least one assigned root sequence is broadcast from each access node. The root sequence can be broadcast in a system information message to provide the root sequence to a wireless device for use in formulating an initial access request to an access node. In an embodiment, the root sequence can be broadcast in a system information block message. Additionally, or alternatively, information derived from a root sequence, such as a preamble, or an index of available preambles, can be broadcast by each access node. A wireless device which received the at least one assigned root sequence (and/or the preamble or index of preambles) can use the received information to determine at least one random access preamble, and can use the preamble to request initial access to the access node, e.g., through a random access procedure. In an embodiment, the at least one root sequence broadcast by the access node can enable a wireless device to determine one or more random access preambles. The wireless device can then use the one or more determined random access preambles to perform a random access procedure to initiate communication with an access node.

FIG. 5illustrates an exemplary processing node500in a communication system. Processing node500comprises communication interface502, user interface504, and processing system506in communication with communication interface502and user interface504. Processing node500can be configured to allocate root sequences to access nodes in a wireless communication system. Processing system506includes storage508, which can comprise a disk drive, flash drive, memory circuitry, or other memory device. Storage508can store software510which is used in the operation of the processing node500. Storage508may include a disk drive, flash drive, data storage circuitry, or some other memory apparatus. Software510may include computer programs, firmware, or some other form of machine-readable instructions, including an operating system, utilities, drivers, network interfaces, applications, or some other type of software. Processing system506may include a microprocessor and other circuitry to retrieve and execute software510from storage508. Processing node500may further include other components such as a power management unit, a control interface unit, etc., which are omitted for clarity. Communication interface502permits processing node500to communicate with other network elements. User interface504permits the configuration and control of the operation of processing node500.

Examples of processing node500include a gateway node and a controller node, such as processing node318. Processing node500can also be an adjunct or component of a network element, such as an element of access node104,302, or another access node as illustrated inFIGS. 1 and 3. Processing node500can also be another network element in a communication system. Further, the functionality of processing node500can be distributed over two or more network elements of a communication system.

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, and that various modifications may be made to the configuration and methodology of the exemplary embodiments disclosed herein without departing from the scope of the present teachings. Those skilled in the art also will appreciate that various features disclosed with respect to one exemplary embodiment herein may be used in combination with other exemplary embodiments with appropriate modifications, even if such combinations are not explicitly disclosed herein. As a result, the invention is not limited to the specific embodiments described above, but only by the following claims and their equivalents.