Patent Application
20080080406
The accompanying figures where like reference numerals refer to identical or functionally similar elements throughout the separate views, and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.
As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure. Further, the terms and phrases used herein are not intended to be limiting; but rather, to provide an understandable description of the invention.
The terms “a” or “an”, as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e., open language). The term coupled, as used herein, is defined as connected, although not necessarily directly, and not necessarily mechanically.
The presently claimed invention, according to an embodiment, overcomes problems with the prior art by optimizing the hardware responsible for wireless communication of information to wireless communication devices. An embodiment of the present invention increases hardware utilization in TDD systems by using multiple frequencies at the system access point (AP) to operate a secondary TDD link out of phase with the primary.
The term wireless communication device is intended to broadly cover many different types of devices that can wirelessly receive signals, and optionally can wirelessly transmit signals, and may also operate in a wireless communication system. For example, and not for any limitation, a wireless communication device can include any one or a combination of the following: a cellular telephone, a mobile phone, a smartphone, a two-way radio, a two-way pager, a wireless messaging device, a laptop/computer, a PDA, an automotive gateway, a residential gateway, and the like.
Exemplary Wireless Communications System
According to an embodiment of the present invention, as shown in
The wireless communications network comprises a mobile phone network, a mobile text messaging device network, a pager network, or the like. An embodiment of the wireless communication network, in accordance with the present invention, is a wireless broadband data network (fixed and/or mobile). Further, the communications standard of the wireless communications network of
In an exemplary embodiment, the wireless communications network is capable of broadband wireless communications utilizing time division duplexing (“TDD”) as set forth, for example, by the IEEE 802.16e standard. The IEEE 802.16e standard is further described in IEEE Std. 802.16e-2005. As will be explained in detail below, the TDD duplexing scheme of the present invention allows for the transmissions of signals in out-of-phase downstream and upstream directions using two frequencies. It should be noted that the present invention is not limited to an 802.16e system for implementing the dual-frequency TDD scheme. Other such standards such as UMTS LTE (Long Term Evolution), and IEEE 802.20 are also applicable.
The wireless communications system 100 also includes one or more APs 108, 110 that serve as access points (AP) for communication between the subscriber devices 104a-n and the rest of the system. Each AP 108, 110 is equipped with an antenna 106 and a transceiver 122 that includes a transmitter 124 and a receiver 126 for wirelessly communicating with the plurality of subscriber devices 104a-n within coverage of the APs 108, 110. Although the subscriber devices 104a-n are shown communicating with AP 108 only, any or all of the subscriber units can move to a cell covered by AP 110 and receive coverage by AP 110.
If more than one AP is utilized, the APs 108, 110 are synchronized with one another. Each AP 108, 110, in one embodiment, includes an AP controller (“APC”) 112. In embodiments of the present invention, the elements of transceivers 122, APCs 112, and antennas 106 may be physically separated or integrated. The synchronization of the access points, in one embodiment, is a time-based synchronization for transmitting and/or receiving wireless data.
In the TDD scheme according to the present invention, a number of subscriber devices 104a-n are organized into groups. The TDD synchronization between the APs 108, 110 ensures that respective subscriber devices 104a-n in a single group are not transmitting while the other subscriber devices in the same group are receiving, and vice-versa.
Each AP 108, 110 (or APC 112 that is coupled to the AP 108, 110) includes, in one embodiment, a synchronization means such as a GPS receiver 216 (
The subscriber devices 104a-n in one embodiment, are capable of wirelessly communicating data using the 802.16e standard or any other communication scheme that supports TDD. As the subscriber devices 104a-n enter a cell, they are synchronized with an AP serving that cell. For example, as the subscriber devices 104a-n enter a cell served by AP 108, they access a TDD ranging channel. A downlink frame received by the subscriber devices 104a-n from AP 108 includes a preamble which gives the subscriber devices 104a-n basic synchronization information. An AP, via the APC 112, can determine a timing delay of a subscriber device based on information received from the device such as on a ranging channel. The AP 108, 110 can then signal the subscriber devices 104a-n to either advance or retard their timing so that the subscriber devices 104a-n are synchronized with other subscriber devices 104a-n in the system. The ranging channel is on the reverse link (from subscriber device to AP) and the signaling of timing advance is on the forward link (from AP to subscriber device).
The synchronization between the subscriber devices 104a-n in a group is a timing synchronization for wirelessly transmitting and receiving data. Therefore, the subscriber devices 104a-n within a single group all transmit and receive data at substantially the same time.
Additionally, the wireless communication system 100 is capable of communicatively coupling the subscriber devices 104a-n to a wide area network 118, a local area network 120, a public switched telephone network 111, the internet 116, and the like, through the wireless communications network 102. Each of these networks has the capability of sending data, for example, a multimedia text message to the subscriber devices 104a-n.
Exemplary Information Processing System
The TX/RX timing synchronization means 216, in one embodiment, is a Global Positioning System (“GPS”) module, which provides a master clock source for the APC 200. For example, the CPU 204 receives the clock source from the GPS module 216 and passes this clock source to a clock distribution module 226. Clock signals for the respective components of the AP 108 are generated, in one embodiment, by the clock distribution module 226 based on the master clock source received from the GPS module 216.
The master clock source provides a timing reference for its AP, which is used to synchronize itself and its respective wireless communication devices for transmission and reception of wireless data. A TX/RX synchronizer 224 uses the timing reference to synchronize the AP for wirelessly transmitting and receiving data. Each of the APs 108, 110 in the wireless communication system 100 are synchronized to a substantially common synchronization timing. In other words, the TX/RX timing synchronization means 216 communicatively coupled to each AP 108, 110 generates a substantially common synchronization timing signal. Therefore, the transmission and reception of data by each AP 108, 110 is synchronized with the other APs 108, 110 in the wireless communication system. For example, the APs 108, 110 are synchronized so that downlink and uplink subframes in a TDD communication frame transmitted by each AP 108, 110 are aligned. In other words, the synchronization ensures that any of the subscriber devices 104a-n of AP 108 are not transmitting/receiving while any other subscriber devices of the TDD system are receiving/transmitting.
In one embodiment, the TX/RX timing synchronization is predefined and common among all of the APs 108, 110. In one embodiment, wireless communication devices that are coupled to the AP 108 are also synchronized for transmission and reception of data. For example, the preamble of a downlink frame includes synchronization information for synchronizing one or more respective subscriber devices 104a-n.
The stability oscillator 210, in one embodiment, is a medium stability oscillator, a high stability oscillator, or the like. The stability oscillator 210 acts as a back-up synchronization device if the TX/RX timing synchronization means 216 fails or if a timing reference signal is lost for any reason. For example, if the TX/RX timing synchronization means 216, the stability oscillator 210 provides a timing frame of reference to the clock distribution module 226. The stability oscillator 210 has a relatively slow drift rate, e.g., 0.8 μs per hour, which extends the survivability of the communications system 100. The synchronization of the APs 108, 110 with respect to a timing frame of reference that is common to the APs 108, 110, in one embodiment, is monitored by a TX/RX synchronization monitor 220.
The TX/RX synchronization monitor 220 detects when a loss of the timing reference has occurred. A timing reference loss can occur, for example, from a failure of the TX/RX timing synchronization means 216, loss of the GPS signal, and the like. Once a loss is detected, a TX/RX synchronization loss timer 222 starts to count a predefined time period. The TX/RX synchronization loss timer 222 is used to determine when a predefined period of time has passed since losing the time reference signal. In one embodiment, the predefined period of time correlates to a known amount of time that the stability oscillator can drift (e.g. maximum clock slip rate) before potential interference between subscriber devices 104a-n occurs.
The guard time updater 202 helps mitigate interference. For example, in an 802.16e system utilizing TDD, a frame comprises, among other things, a downlink portion, uplink portion, a transmit turn guard (“TTG”) portion, and a receive turn guard (“RTG”) portion. The transmit turn guard is a time period where the subscriber device 104 is transitioning from a transmitting mode to a receiving mode. In other words, the wireless communication device stops transmitting so that it can receive data from the AP 108. The receive turn guard is a time period where the subscriber device 104 is transitioning from a receiving mode to a transmitting mode.
Once the predefined time period corresponding to the maximum drift rate has passed, the guard time updater 202 decreases the available amount of transmission time for the AP 108 and its respective subscriber devices 104a-n by increasing the guard times in the frame. For example, the guard time updater 202 increases the TTG by one symbol time in both directions, e.g. before and after the TTG. The RTG is also increased by one symbol time in both directions. Therefore, the downlink portion, which is the portion of the frame where the AP 108 is transmitting, is decreased by two symbol times. The uplink portion of the frame, which is where subscriber devices 104a-n are transmitting, is also decreased by two symbol times. It should be noted that the TTG and RTG can be increased by more than one symbol time. It should also be noted that symbol times can be different and do not have to be fixed for all symbols.
When the timing reference is lost, uncertainty exists as to whether the AP 108 is transmitting/receiving at the same time, before, or after the other AP 110, thereby potentially causing interference. The adjustment of the guard times allows for this uncertainty to be removed. Adjusting the guard times prevents one subscriber device from transmitting to its AP while another subscriber device is listening to its AP and vice versa, which can cause interference.
The network adapter hardware 215 is used to provide an interface to the network 102. For example, the network adapter 215, in one embodiment provides the Ethernet connections 136, 138 between the AP 108, 110 and the wireless communications network 102. An embodiment of the present invention can be adapted to work with any data communications connections including present day analog and/or digital techniques or via a future networking mechanism.
Although the exemplary embodiments of the present invention are described in the context of a fully functional computer system, those skilled in the art will appreciate that embodiments are capable of being distributed as a program product via floppy disk, e.g. floppy disk 228, CD ROM, or other form of recordable media, or via any type of electronic transmission mechanism.
Exemplary Wireless Communication Device
In transmit mode, the device controller 302 electrically couples the antenna 304, through the transmit/receive switch 306, to a transmitter 310. The device controller 302 operates the transmitter and receiver according to instructions stored in the memory 312. These instructions include, for example, a neighbor cell measurement-scheduling algorithm. The memory 312 also includes a TX/RX timing synchronizer 314. The TX/RX timing synchronizer 314 synchronizes the subscriber device 300 with its respective AP 108 for transmitting and receiving wireless information. For example, as the subscriber device 300 enters into a cell, it communicates with an AP, such as AP 108, via a ranging channel. The APC 112 determines, in one embodiment, a timing scheme needed to synchronize the subscriber device with the other subscriber devices and APs in the system 100. The subscriber device 300 receives a timing synchronization signal via the receiver 126 transmitted from the AP 108 on a reverse link. The timing synchronization signal instructs the TX/RX timing synchronizer 314 to advance or retard a timing reference of the subscriber device 300, thereby synchronizing the subscriber device 300 with the other devices in the system 100.
The subscriber device 300 also includes non-volatile storage memory 316 for storing, for example, an application waiting to be executed (not shown) on the subscriber device 300. The subscriber device 300, in this example, also includes an optional local wireless link 318 that allows the subscriber device 300 to directly communicate with another subscriber device without using a wireless network (not shown). The optional local wireless link 318, for example, is provided by Bluetooth, Infrared Data Access (IrDA) technologies, or the like. The optional local wireless link 318 also includes a local wireless link transmit/receive module 320 that allows the subscriber device 104 to directly communicate with another wireless communication device.
The subscriber device 300 of
The subscriber device 300 also includes a microphone 330 for allowing a user to input audio signals into the subscriber device 300. Sound waves are received by the microphone 330 and are converted into an electrical audio signal. Audio input conditioning circuits 332 receive the audio signal and perform various conditioning functions on the audio signal, for example, noise reduction. An audio input controller 334 receives the conditioned audio signal and sends a representation of the audio signal to the device controller 302.
In some embodiments, the subscriber device 300 also comprises a keyboard 336 for allowing a user to enter information into the subscriber device 300. The subscriber device 300 further comprises a camera 338 for allowing a user to capture still images or video images into memory 314. Furthermore, the subscriber device 300 includes additional user input interfaces 340, for example, touch screen technology (not shown), a joystick (not shown), or a scroll wheel (not shown). In one embodiment, a peripheral interface 350 is also included for allowing the connection of a data cable to the subscriber device 300. The peripheral interface 350 allows the subscriber to act as a residential gateway providing, for example, an Ethernet data connection to the user. In another exemplary application, the peripheral connection 350 allows a subscriber to plug a PCMCIA card into a laptop. The card provides a wireless network connection for the laptop. In one embodiment of the present invention, the connection of a data cable allows the subscriber device 104 to be connected to a computer or a printer.
A visual notification (or indication) interface 342 is also included on the subscriber device 300 for rendering a visual notification (or visual indication), for example, a sequence of colored lights on the display 346 or flashing one or more LEDs (not shown), to the user of the subscriber device 300. For example, a received multimedia message may include a sequence of colored lights to be displayed to the user as part of the message. Alternatively, the visual notification interface 342 can be used as an alert by displaying a sequence of colored lights or a single flashing light on the display 346 or LEDs (not shown) when the subscriber device 104 receives a message, or the user missed a call.
The subscriber device 300 also includes a tactile interface 344 for delivering a vibrating media component, tactile alert, or the like. For example, a multimedia message received by the subscriber device 300, may include a video media component that provides a vibration during playback of the multimedia message. The tactile interface 344, in one embodiment, is used during a silent mode of the subscriber device 300 to alert the user of an incoming call or message, missed call, or the like. The tactile interface 344 allows this vibration to occur, for example, through a vibrating motor or the like.
The subscriber device 300 also includes a display 346 for displaying information to the user of the subscriber device 300 and an optional Global Positioning System (GPS) module 348. The optional GPS module 348 determines the location and/or velocity information of the subscriber device 300. This module 348 uses the GPS satellite system to determine the location and/or velocity of the subscriber device 300. Alternative to the GPS module 348, the subscriber device 300 may include alternative modules for determining the location and/or velocity of subscriber device 300, for example, using cell tower triangulation and assisted GPS.
Single-Frequency TDD Frames
Dual-Frequency TDD Frames
Described now is a specific embodiment of the dual-frequency wireless TDD communication scheme, according to the present invention. The inventive dual-frequency scheme, illustrated in
Referring now back to
More specifically, in the first period T1 of the time frame 500, the AP transmitter 124 of AP 108 transmits to a first group of subscriber devices 104a-n in the first link 502 a first frequency, f1. Contemporaneously with the transmission at frequency f1, the receiver 126 receives data from the second group of subscriber devices 106a-n at the second frequency f2 via the second link 504. Because the transmission and reception frequencies are different, the AP 108 is now able to receive while it is transmitting, and vice versa, without interference.
The AP 108 then enters a transmit turn guard period T2 where it switches, on the first link 502, from frequency f1 to frequency f2 and on the second link 504, from frequency f2 to frequency f1. Upon exiting the transmit turn guard period T2, the system enters the next period T3, where the AP 108 transmits on the first link 502 to the second group of subscriber devices 106a-n in the second frequency f2 and receives data in the second link 504 from the first group of subscriber devices 104a-n in the first frequency f1. At the end of the third period T3, the AP 108 enters a second transmit turn guard period T4, where it switches on the first link 502 back to the first frequency f1 and on the second link back to the second frequency f2. The process continues to alternate as shown in the remainder of
As has now been described and shown in the illustration of
Distinct from a frequency duplexed system (FDD), where receive and transmit functions are performed on separate frequencies, the present invention provides different groups of TDD subscriber devices operating on separate frequencies or frequency bands.
Exemplary Process of Transmitting in Dual-Frequency TDD Mode
Non-Limiting Examples
The foregoing embodiments of the present invention are advantageous because they provide a method of increasing hardware utilization and system capacity in TDD systems by using multiple frequencies at the system AP or access point to operate a secondary TDD link out of phase with the primary link. Through utilization of the present invention, during times when the AP transmitter is normally idle, it now communicates to another set of subscriber devices on a different frequency. The process operates similarly for the receive side. The present invention is advantageous as it provides a low-cost, multi-carrier AP implementation without any need to modify currently used subscriber devices.
Although specific embodiments of the invention have been disclosed, those having ordinary skill in the art will understand that changes can be made to the specific embodiments without departing from the spirit and scope of the invention. The scope of the invention is not to be restricted, therefore, to the specific embodiments, and it is intended that the appended claims cover any and all such applications, modifications, and embodiments within the scope of the present invention.
