Patent Publication Number: US-2007104176-A1

Title: System and method for pilot signal utilization in an environment using dynamic frequency assignment

Description:
CLAIM OF PRIORITY  
      This application claims priority from U.S. Provisional Patent Application Ser. No. 60/735,972, filed on Nov. 10, 2005, and entitled “SYSTEMS AND METHODS FOR COMMUNICATIONS”, which is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND  
      Wireless communication systems use frequency channels to communicate with wireless devices. The frequency channels may be divided into downlink and uplink channels when communicating with a wireless device. The downlink channel is for communications sent from the system to the wireless device and the uplink channel is for communications sent from the wireless device to the system. Generally, the frequency channels in a large scale wireless system are predefined. For example, in wireless systems based on technologies such as code division multiple access (CDMA) or Global System for Mobile communication (GSM), the downlink and uplink channel frequencies may be predetermined and assigned to the system. The frequency channel assignments may take such issues as inter-cell interference into consideration. In such systems, due to the assigned frequency channels and predefined downlink/uplink channel pair relationships, the wireless device may automatically know the frequency of the uplink channel after synchronizing to a corresponding downlink channel.  
      However, in wireless systems using dynamically assigned frequencies, there may not be predefined frequency channel assignments and/or predefined relationships between the downlink and uplink channels. Accordingly, what is needed are a system and method for notifying a wireless device of available downlink and uplink channels and enabling the wireless device to communicate with the system using those channels.  
     SUMMARY  
      In one embodiment, a method for a wireless device comprises identifying a pilot signal of a base station in a frequency division duplex wireless system, and obtaining a reverse access channel identifier and a forward signaling channel identifier from the pilot signal. The method initiates communication with the base station via a reverse access channel corresponding to the reverse access channel identifier, senses a set of candidate channels available for use by the wireless device, and reports the set of candidate channels to the base station.  
      In another embodiment, a wireless device comprises a wireless interface configured to receive and transmit wireless signals, a processor coupled to the wireless interface, a memory coupled to the processor and configured to store a plurality of instructions, and the plurality of instructions. The plurality of instructions includes instructions for searching for a pilot signal transmitted by a base station in a frequency division duplex wireless network, obtaining reverse access channel information from the pilot signal, obtaining forward signaling channel information from the pilot signal, and contacting the base station via a reverse access channel extracted from the reverse access channel information. The instructions also include instructions for receiving a first directive from the base station via a forward signaling channel extracted from the forward signaling channel information to search for a first set of candidate channels, searching for the first set of candidate channels, and reporting at least one candidate channel identified during the search for the first set of candidate channels to the base station.  
      In yet another embodiment, a method for use by a base station comprises generating a pilot signal in a frequency division duplex wireless system, wherein the pilot signal includes uplink and downlink information. A message is received from a wireless device via an uplink channel defined in the uplink information and the wireless device is instructed to sense a first set of candidate channels via a downlink channel defined in the downlink information. A notification is received from the wireless device identifying at least one candidate channel available for use by the wireless device from the first set of candidate channels, and the wireless device is instructed to use at least one of the candidate channels from the first set of candidate channels identified as available for use.  
      In still another embodiment, a wireless communication system comprises a subdivision of a frequency division duplex wireless network and a base station providing wireless coverage for the subdivision, wherein the base station is coupled to a processor configured to execute instructions stored on a memory. The instructions include instructions for generating a pilot signal containing reverse access channel information and forward signaling channel information, receiving a message from a wireless device via a reverse access channel defined in the reverse access channel information, and instructing the wireless device via a forward signaling channel associated with the forward signaling channel information to use first and second frequency channels for downlink and uplink channels, respectively. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is emphasized that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.  
       FIG. 1  is a flowchart illustrating one embodiment of a method for establishing a connection between a user device and a base station using uplink and downlink channel information contained in a pilot signal transmitted by the base station.  
       FIG. 2  is a diagram of one embodiment of a network in which the method of  FIG. 1  may be implemented.  
       FIG. 3  is a flowchart illustrating another embodiment of a method for establishing a connection between a user device and a base station using uplink and downlink channel information contained in a pilot signal transmitted by the base station.  
       FIG. 4  is a flowchart illustrating still another embodiment of a method for establishing a connection between a user device and a base station using uplink and downlink channel information contained in a pilot signal transmitted by the base station.  
       FIG. 5  is a diagram of another embodiment of a network in which the method of  FIG. 1  may be implemented.  
       FIG. 6  is a block diagram of one embodiment of a simplified user device.  
       FIG. 7  is a sequence diagram illustrating an embodiment of a sequence of events for establishing a connection between a user device and a base station of  FIG. 5  using uplink and downlink channel information contained in a pilot signal transmitted by the base station. 
    
    
     DETAILED DESCRIPTION  
      It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.  
      Referring to  FIG. 1 , in one embodiment, a method  100  may be used by a user device (which may be referred to as Customer Premises Equipment (CPE)) to establish a connection with an access point (e.g., a base station (BS)) in a frequency division duplex (FDD) wireless system. In the present example, the wireless system may be a wireless regional access network (WRAN) that uses dynamic frequency selection. In such a wireless system, a dynamic frequency selection process may be used to identify and select frequencies for use by the system instead of relying on the assignment of predetermined frequencies. One example of dynamic frequency selection is described in U.S. patent application Ser. No. (Attorney Docket No. 2005.11.005.WS0/1005.10), filed on Sep. 25, 2006, and entitled “SYSTEM AND METHOD FOR DYNAMIC FREQUENCY SELECTION BASED ON SPECTRUM ETIQUETTE”, which is hereby incorporated by reference.  
      Dynamic frequency selection may be desirable, for example, as more of the frequency spectrum becomes available for license-exempted or light-licensing operations. In systems based on such concepts, each subdivision (e.g., cell or sector) of a network may dynamically identify and select frequencies with the consideration of avoiding inter-cell interference. The need for accomplishing such identification and selection dynamically is due in part to the difficulty of advance frequency planning in systems where frequency availability changes over time. In systems that must handle changing frequency availability, a centralized decision-making scheme may present issues such as scalability and point-of-failure. Although some simple schemes may exist for spectrum sharing negotiations between, for example, two neighboring cells, such schemes do not adequately the need for systematic dynamic frequency-sharing in large-scale wireless systems. Accordingly, dynamic frequency assignment processes may be used.  
      Due to the use of dynamically assigned frequencies, there may be no predefined relationship between downlink and uplink frequencies. In such a system, the CPE may not be allowed to initiate a transmission using any frequency unless directed by a BS to do so in order to avoid interference. However, in order to initiate the establishment of a connection with the system, the CPE may need information about how to contact the BS. Accordingly, as described below, the CPE may use information transmitted in a pilot signal generated by the BS in order to establish a connection. In addition, a downlink signaling channel also needs to be indicated so the BS can communicate with the CPE. This information may also be determined from information transmitted in the pilot signal.  
      In step  102 , the CPE may identify a pilot signal from a BS. As will be described later in greater detail, the pilot signal may include information such as a BS identifier, downlink channel information, and uplink channel information. In the present example, the uplink channel information may include channel characteristics of a reverse access channel (RACH), such as frequency, bandwidth, power requirements, and/or parameters for resolving RACH contention. The uplink information carried by the pilot signal may vary depending on such factors as the particular configuration of the wireless system. For example, if the wireless system operates with a known RACH power requirement, then the power requirement may not be transmitted in the pilot signal. In the present example, the downlink channel information may include channel characteristics of a forward signaling channel (FSCH), such as frequency and bandwidth. The downlink information carried by the pilot signal may vary depending on such factors as the particular configuration of the wireless system.  
      It is understood that the uplink channel may include channels other than the RACH, and that the pilot signal may carry uplink information on other channels in some embodiments. Likewise, it is understood that the downlink channel may include channels other than the FSCH, and that the pilot signal may carry downlink information on other channels in some embodiments. For example, in a TDMA system, the uplink channel may be divided into traffic channels and signaling channels, and the signaling channels may be further divided into one or more broadcast channels, common control channels (which may include the RACH), and dedicated/associated control channels. Accordingly, although the present disclosure describes a pilot signal containing RACH and FSCH information for purposes of example, the present disclosure is not limited to RACH and FSCH information.  
      In step  104 , the CPE may obtain the RACH ID and other RACH information as well as the FSCH ID and other FSCH information from the pilot signal and use the obtained information to initiate contact with the BS in step  106 . In step  108 , the CPE may sense candidate channels that are available for use by the CPE and report the candidate channels to the BS. For example, as will be described in greater detail with respect to  FIG. 2 , the CPE may sense television (TV) spectrum frequencies that are available (in terms of adequate power, etc.) to the CPE. These frequencies may then be reported to the BS.  
      In step  110 , the BS uses the FSCH to direct the CPE to use a specific uplink channel and downlink channel for data transfer. In some embodiments, the BS may select the uplink and downlink channels from the candidate channels reported by the CPE in step  106 . Accordingly, by receiving a pilot signal from the BS containing the information needed to communicate with the BS prior to knowing the downlink and uplink channel frequencies, the CPE may operate within the dynamic frequency assignment environment of the wireless network even though the CPE may not be allowed to initiate a transmission without first receiving permission from the BS (e.g., via the RACH information). Following step  110 , the CPE and the BS use the assigned uplink and downlink channels for data transfer.  
      Referring to  FIG. 2 , one embodiment of a portion of a wireless network  200  is illustrated with cells  202   a  and  202   b  and corresponding BSes  204   a  and  204   b . It is understood that the cells  202   a  and  202   b  may represent any subdivision (e.g., a cell, sector, or other network segment) of a wireless communication network, and that the terms “cell” and “sector” may be interchangeable depending on the configuration of a particular network. Although not shown, it is understood that BS  204   a  and BS  204   b  may include processors, memories, and other components that enable the base stations to receive, store, retrieve, process, and transmit instructions and data over wireless and/or wireline communication links. Furthermore, at least some functionality of a base station may be distributed and located elsewhere, either within a cell or outside of a cell. Repeaters (not shown) may be used to extend the range of the BS  204   a  and/or the BS  204   b.    
      In the present example, the network  200  may be a WRAN, but it is understood that the wireless network  200  may represent many different types of wireless networks. In some embodiments, the wireless network  200  may be configured to use available television (TV) spectrum frequencies in certain areas (e.g., rural areas) to provide additional bandwidth to user terminals. For example, a fixed point-to-multipoint WRAN may be configured to use ultra high frequency and very high frequency (UHF/VHF) TV bands between 54 and 862 MHz. Such specifications may comply, for example, with those developed by the Institute of Electrical and Electronics Engineers (IEEE) 802.22 Working Group on WRANs. It is understood, however, that the present disclosure is not limited to TV spectrum frequencies and that other frequencies may be used in place of or in addition to those in the TV spectrum.  
      In the present example, the cells  202   a  and  202   b  are shown in a sectorized configuration. More specifically, the cell  202   a  is divided into sectors  206   a - 206   f  and the cell  202   b  is divided into sectors  208   a - 208   f . To avoid inter-cell and inter-sector interference, neighboring cells and/or sectors should generally cooperate when deciding what frequency bands to use. In the network  200 , each cell  202   a  and  202   b  may pick up an available frequency band dynamically, which forecloses the possibility of advance frequency planning and assignment. Without cooperation between the cells and/or sectors, the frequency selection in a particular cell may prevent neighboring cells from properly functioning. For example, assume that the available frequency channels at BS  204   a  and BS  204   b  are { 1 ,  3 } and { 1 ,  2 ,  3 }, respectively. If BS  204   b  decides to use channels { 1 ,  3  }, then BS  204   a  has no available channel. Furthermore, cooperation may be used to facilitate load balancing within the wireless network  200 . For example, if BS  204   a  is heavily loaded (e.g., has a large amount of traffic) and BS  204   b  is not heavily loaded, then BS  204   a  may use { 1 ,  3 } and BS  204   b  may use { 2 }. This provides BS  204   a  with additional bandwidth to handle its heavier load while allowing BS  204   b  to still provide service. Accordingly, each BS  204   a  and  204   b  may be configured to dynamically select frequencies to be used in its corresponding cells and/or sectors.  
      In the present example, each BS  204   a  and  204   b  may generate a pilot signal containing information such as a WRAN ID, BS ID, downlink channel information, and uplink channel information. The pilot signal may be designed to provide information to a CPE (not shown) in order for aid the CPE in frequency synchronization, timing synchronization, acquiring the WRAN ID and BS ID, and acquiring characteristics of the RACH such as frequency, bandwidth, power requirements, and/or parameters for resolving RACH contention (e.g., using slotted Aloha). The downlink channel information may contain similar information for the FSCH. By providing RACH and FSCH information and/or other needed uplink or downlink information in a pilot signal used in the wireless network  200 , the CPE may communicate with the wireless network despite the wireless network&#39;s use of dynamic frequency assignments and any prohibition on transmission by the CPE without authorization from the wireless network.  
      Referring to  FIG. 3 , in another embodiment, a method  300  may be used by a BS (e.g., the BS  204   a  of  FIG. 2 ) within a system that uses dynamic frequency assignment, such as the wireless network  200  of  FIG. 2 . In step  302 , in addition to BS ID and downlink channel information that may be traditionally transmitted in a pilot signal, the BS  204   a  may generate a pilot signal containing uplink channel information. The uplink information may include characteristics of a RACH (e.g., frequency, bandwidth, power requirements, and/or parameters for resolving RACH contention). The downlink information may include characteristics of a FSCH (e.g., frequency and/or bandwidth). In the present example, the CPE may only have permission to communicate with the BS  204   a  via the RACH at this time.  
      In step  304 , the BS  204   a  may receive a communication from a CPE on the RACH. In step  306 , the BS  204   a  may instruct the CPE using the FSCH to sense candidate channels that are available for use by the CPE. In the present example, the BS  204   a  may send a set of candidate channels to the CPE and instruct the CPE to determine whether it can detect any of the candidate channels. In other embodiments, the BS  204   a  may instruct the CPE to sense all available channels, or the CPE may sense the available candidate channels without being instructed by the BS  204   a . In step  308 , the BS  204   a  may receive a list of candidate channels sensed by the CPE. The list may include only candidate channels from a set provided by the BS  204   a  or may include all candidate channels.  
      In step  310 , the BS  204   a  may determine whether the candidate channels (if any) reported by the CPE are acceptable. For example, if the CPE detected and reported all candidate channels to the BS  204   a , the BS  204   a  may determine if any of the candidate channels can be used by the CPE without causing interference. If the CPE detected and reported only candidate channels from a list sent by the BS  204   a , then step  310  may involve determining if the reported list of candidate channels contains the number of channels needed (e.g., for downlink and uplink channels). If the reported candidate channels are not acceptable (in number or otherwise), the method  300  may return to step  306 . If acceptable candidate channels exist, the BS  204   a  may select one or more of the acceptable channels and instruct the CPE via the FSCH to use the selected channels in step  312 . If only one channel is available and two or more are needed (e.g., for downlink and uplink), the BS  204   a  may reserve the available channel and may instruct the CPE to search for other candidate channels, may wait until a candidate channel is released for use by the CPE, or may request that a channel be released.  
      Referring to  FIG. 4 , in another embodiment, a method  400  may be used by a CPE within a system that uses dynamic frequency assignment, such as the wireless network  200  of  FIG. 2 . In step  402 , the CPE may search for a pilot signal, such as a pilot signal generated by the BS  204   a  of  FIG. 2 . In the present example, the CPE may not be allowed to initiate a transmission on any frequency at this time. If no pilot signal is found, as determined in step  404 , the CPE may return to step  402  and continue searching. If a pilot signal is found, the method  400  may continue to step  406 , where the CPE synchronizes with the BS  204   a  using information from the pilot signal. It is noted that the CPE may find multiple pilot signals in step  402 . If multiple pilot signals were found in step  402 , the CPE may identify a primary pilot signal based on signal strength and/or other factors and synchronize with the BS corresponding to the primary pilot signal.  
      In step  408 , the CPE may obtain a RACH ID and/or other RACH information from the pilot signal, along with a FSCH_ID and/or other FSCH information. The CPE may then attempt to associate with the BS  204   a  using the RACH. In the present example, the CPE may not be allowed to initiate a transmission on any frequency except the RACH at this time. In step  410 , the CPE may receive instructions on the FSCH from the BS  204   a  to search for candidate channels. The instructions may include a set of candidate channels for which the CPE is to search or may instruct the CPE to search for all available channels. In some embodiments, step  410  may be omitted and the CPE may search for available candidate channels without being instructed by the BS  204   a . In step  412 , the CPE may search for candidate channels and report the channels that are available for use by the CPE, which may include TV frequencies and/or other frequencies.  
      In step  414 , the CPE may determine whether it has received a channel designation from the BS  204   a  notifying the CPE to use one or more of the candidate channels. If no such channels have been designated, the method  400  may receive instructions to search for other candidate channels (step  410 ). If the CPE determines that the BS  204   a  has designated channels for use by the CPE, the CPE may begin to communicate using the designated channels in step  416 .  
      Referring to  FIG. 5 , a communications network  500  illustrates another embodiment of a system within which the method  100  of  FIG. 1  may be executed. In the present example, the network  500  is a time division multiple access (TDMA) network that may be compatible with a variety of standards including, but not limited to, Global System for Mobile communication (GSM), General Packet Radio Service (GPRS), and Enhanced Data Rates for GSM Evolution (EDGE). The network  500  may include WRAN functionality as well as, for example, GSM functionality.  
      The network  500  includes a plurality of cells  202   a ,  202   b  (e.g., the cells  202   a  and  202   b  of  FIG. 2 ). In the present example, the network  500  is a wireless network, and may be connected to other wireless and/or wireline networks, such as a Public Switched Telephone Network (PSTN)  502   a  and a packet network  502   b . Each cell  202   a ,  202   b  in the network  500  includes a base station (BS)  204   a ,  204   b , respectively, that are coupled to base station controllers (BSC)  504   a ,  504   b , respectively. A mobile switching center (MSC)  506  may be used to connect the network  500  with other networks such as the PSTN  502   a . Although not shown, the base stations  204   a  and  204   b  may be coupled to the same BSC, and the BSCs  504   a  and  504   b  may be coupled to separate MSCs. The BSC  504   b  may be coupled to a packet-switched node  508  (e.g., a packet data node such as a packet data serving node (PDSN)) that is coupled to the packet network  502   b . It is understood that other network components, such as a Gateway Mobile Switching Center (GMSC), Home Location Register (HLR), Visitor Location Register (VLR), Authentication Center (AuC), Equipment Identity Register (EIR), and/or a Short Message Service Gateway, are not shown for purposes of clarity but may be included in the network  500 . As such components are well known to those of skill in the art, they are not described in detail herein.  
      The network  500  enables a wireless device  510  (e.g., a CPE) to communicate with another device (not shown) via the BS  204   a  associated with the cell  202   a  in which the CPE is located. Although illustrated in  FIG. 5  as a cellular phone, it is understood that the CPE  510  may be any device capable of wirelessly participating in a communication session, and such devices may include personal digital assistants, modems, computers, pagers, and/or telephones. The cells  202   a ,  202   b  overlap so that the CPE  510  (if mobile) may travel from one cell to another (e.g., from the cell  202   a  to the cell  202   b ) while maintaining a communication session. In a handoff region  512  (e.g., the area where the cells  202   a ,  202   b  overlap), the CPE  510  may be serviced by both the BS  204   a  and the BS  204   b . Pilot signals transmitted by the BS  204   a  and/or  204   b , at least for a WRAN portion of the network  500 , may include uplink and downlink information as previously described.  
      Referring to  FIG. 6 , one embodiment of a simplified CPE  600  is illustrated. The CPE  600  may include a central processing unit (“processor”)  602 , a memory unit  604 , an input/output (“I/O”) interface  606 , and a wireless interface  608 . The wireless interface  608  may be, for example, one or more wireless network interface cards (NICs) that are each associated with a media access control (MAC) address. The wireless interface  608  may be coupled directly to a network (not shown) or may be coupled via one or more other networks (not shown). The components  602 ,  604 ,  606 , and  608  may be interconnected by a bus system  610 .  
      It is understood that the CPE  600  may be differently configured and that each of the listed components may actually represent several different components. For example, the processor  602  may represent a multi-processor or a distributed processing system; the memory unit  604  may include different levels of cache memory, main memory, hard disks, and remote storage locations; and the I/O device  606  may include monitors, keyboards, and the like. Furthermore, although shown within the CPE  600 , it is understood that some components (e.g., a keyboard or antenna) may be physically located outside of the CPE  600 . In addition, some or all of the components  602 ,  604 ,  606 , and  608  may be distributed. Therefore, a wide range of flexibility is anticipated in the configuration of the CPE  600 .  
      Referring to  FIG. 7 , in yet another embodiment, a sequence diagram  700  illustrates one possible sequence of events between the CPE  510  and BS  204   a  of  FIG. 5 . In the present example, the sequence diagram  700  illustrates the CPE  510  moving from a powered off state to a powered on state. In step  702 , the BS  204   a  is transmitting a pilot signal containing uplink and downlink information as previously described. In step  704 , the CPE  510  may be powered on and may detect the pilot signal transmitted by the BS  204   a  (step  706 ). The CPE  510  may synchronize with the BS  204   a  in step  708  and may extract a RACH ID and/or other uplink information as well as an FSCH ID and/or other downlink information from the pilot signal in step  710 . In step  712 , using the RACH ID and the FSCH ID, the CPE  510  may associate with the BS  204   a . It is understood that the CPE  510  may search for and identify candidate channels, report those channels to the BS  204   a , and receive instructions to use one or more of the candidate channels from the BS during the sequence illustrated by the sequence diagram  700 .  
      Although only a few exemplary embodiments of this disclosure have been described in details above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this disclosure. Also, features illustrated and discussed above with respect to some embodiments can be combined with features illustrated and discussed above with respect to other embodiments. For example, various steps from different flow charts may be combined, performed in an order different from the order shown, or further separated into additional steps. Furthermore, steps may be performed by network elements other than those disclosed. Accordingly, all such modifications are intended to be included within the scope of this disclosure.