Patent Application
20070183385
1. Field
The present disclosure is directed to a method and apparatus for distinguishing a frame on a channel shared by multiple users. More particularly, the present disclosure is directed to a method and apparatus for using a unique identifier on a scrambled signal to determine whether a frame is intended for a specific user.
2. Description of Related Art
Presently, during a broadcast multicast services session, a forward dedicated control channel can be used for signaling addressed to an individual mobile station. The single forward dedicated control channel can be shared by multiple mobile stations by using time division multiplexing and using a long code mask to scramble the signaling so only a specific mobile station can read the signaling. The mobile station can then use its own long code mask to descramble the received symbols and then do decoding and cyclic redundancy code checking. The mobile station can determine it received the frame correctly if it passes cyclic redundancy code checking.
Unfortunately, since both using the wrong long code mask and decoding errors can lead to cyclic redundancy code checking failures, the mobile station cannot distinguish between an erasure or improperly received signal due to decoding error and a frame intended for another mobile station that uses the same forward dedicated control channel. Also, a mobile station cannot utilize cyclic redundancy code checking to determine a discontinuous transmission when the forward dedicated control channel is turned off. Furthermore, because the mobile station cannot distinguish between sources of cyclic redundancy coding check failures, the mobile station cannot adequately determine when to increase or decrease an outer loop power setpoint to account for erasures.
The embodiments of the present invention will be described with reference to the following figures, wherein like numerals designate like elements, and wherein:
The disclosure provides an apparatus and method of distinguishing a frame on a channel shared by a plurality of users. According to one embodiment, a unique identifier can be obtained for each of a set of communication devices. A message intended for one of the communication devices can be obtained. The message can be scrambled using a long code generated using a communication device specific long code mask to obtain a scrambled message. The unique identifier can be incorporated into the scrambled message for a frame intended for a selected communication device. The frame can then be transmitted. According to a related embodiment, a radio frequency signal can be received at a communication device for the frame. Demodulation can be performed on the signal to obtain a scrambled signal. A unique identifier can be extracted from the scrambled signal. The unique identifier extracted from the scrambled signal can be examined to determine if the signal is intended for the communication device.
In an exemplary embodiment, the network controller 140 is connected to the network 110. The network controller 140 may be located at a base station, at a radio network controller, or anywhere else on the network 110. The network 110 may include any type of network that is capable of sending and receiving signals, such as wireless signals. For example, the network 110 may include a wireless telecommunications network, a cellular telephone network, a cdma2000 network, W-CDMA network, a satellite communications network, and other like communications systems capable of sending and receiving communication signals. Furthermore, the network 110 may include more than one network and may include a plurality of different types of networks. Thus, the network 110 may include a plurality of data networks, a plurality of telecommunications networks, a combination of data and telecommunications networks and other like communication systems capable of sending and receiving wireless messaging service messages.
In operation, according to one embodiment, the network controller 140 can obtain a unique identifier for each of the terminals 120 and 130. This unique identifier may be obtained from the terminals, from a local database, by assigning them, or from any other resource. The unique identifier can be a mobile communication device or mobile station identification number, a subscriber identity, or any other identifier that can be used to uniquely identify a terminal on a shared channel. The unique identifier can also be a mobile communication device identity code generated by performing length 16 Walsh block coding on the mobile communication device identification number.
The network controller 140 can obtain a message intended for one of the terminals 120. This message may be a message to be sent on a forward dedicated control channel during a broadcast multicast session. The network controller 140 can scramble the message. For example, the network controller 140 can scramble the message using a long code generated using a mobile communication device-specific long code mask to obtain a scrambled message. The network controller 140 can then incorporate the unique identifier into the scrambled message for a frame intended for the selected mobile communication device 120. For example, the network controller 140 can append the unique identifier to the scrambled message, puncture the unique identifier into a power control section or any portion of the scrambled message, or otherwise incorporate the unique identifier into the scrambled message. The network controller 140 can then transmit the frame. For example, the network controller 140 can transmit the frame on a forward dedicated control channel.
According to another related embodiment, the network controller 140 can identify a set of mobile communication devices 120 and 130. For example, these mobile communication devices may be devices that are receiving broadcast multicast services. The controller can then obtain a unique identifier for at least one of the mobile communication devices 120. The network controller 140 can obtain information bits, such as a message, intended for the mobile communication device 120. This message may be a message to be sent on a forward dedicated control channel during a broadcast multicast session. The network controller 140 can then append cyclic redundancy code bits to the information bits to obtain a cyclic redundancy coded message. The network controller 140 can perform channel coding on the cyclic redundancy coded message to obtain a channel coded message. The network controller 140 can then scramble the message using a long code generated using a mobile communication device-specific long code mask to obtain a scrambled message. The network controller 140 can incorporate the unique identifier into the scrambled message for a frame intended for the selected mobile communication device 120. For example, the network controller 140 can append the unique identifier to the scrambled message, puncture the unique identifier into a power control section or any portion of the scrambled message, or otherwise incorporate the unique identifier into the scrambled message. As another example, the network controller 140 can puncture the unique identifier by inserting the unique identifier into a power control subchannel section of the scrambled message. The network controller 140 can then transmit the frame. For example, the network controller 140 can transmit the frame on a forward dedicated control channel intended for the selected mobile communication device 120.
According to another related embodiment, when the network controller 140 uses a forward dedicated control channel or forward fundamental channel in a broadcast multicast service to carry signaling to different terminals 120 and 130, the network controller 140 can puncture a unique identifier corresponding to a desired terminal 120 into the forward channel where power control bits are typically punctured. If cyclic redundant code checking fails at the terminal 120 after receiving a frame, the terminal 120 can look at the unique identifier to see if the frame is targeted to the terminal 120. Thus, the terminal 120 can distinguish between erasures and frames targeted to other terminals. The terminal 120 can also thus distinguish between erasures and discontinuous transmissions. Accordingly, the outer loop residing on a terminal 120 can be driven only by the frames targeted to the terminal 120 and a power setpoint can be increased based on erasures of frames due to decoding error of the frames targeted for the terminal 120.
To generate good reception of the unique identifier, at the network controller 140, a reliable error correction coding can be used for the unique identifier. For example, block coding can be used to map a 4-bit unique identifier into a length-16 Walsh code. To do this, the decimal representation of the 4-bit number can be used to index a row in a 16×16 Hadamard matrix. The resulting Walsh code can then be punctured onto a forward dedicated control channel or a forward fundamental channel. Then, at the terminal 120, a block decoder can be used to detect whether the unique identifier is present or not on the forward dedicated control channel or the forward fundamental channel.
Inner loop power control can be carried out quickly, for example, at say 800 Hz. To do this, a terminal 120, such as a communication device, can measure a received signal strength and compare it against a threshold stored in the communication device. Where the received signal strength can be Eb/Nt where Eb is bit energy and Nt is noise spectrum density. If the received Eb/Nt is greater than the threshold, the communication device can instruct a base station or network controller 140 to power down, for example by 0.5 dB, so the communication device can instruct the base station or network controller 140 to lower its transmission power. If the received Eb/Nt is less than the threshold, the communication device can instruct the base station or network controller 140 to power up, for example by 0.5 dB, so the communication device can instruct the base station or network controller 140 to raise its transmission power. The setpoint can also be any derivative from Eb/Nt threshold. Outer loop power can be slower, for example, 50 Hz. Here, when the mobile detects a frame error, it can increase the outer loop threshold, for example, by 0.5 dB. When the communication device detects a successful frame, it can decrease the outer loop threshold, for example, by 0.5 dB/99. This process of changing the received Eb/Nt threshold according to whether a frame is in error or not allows the mobile target an frame error rate, e.g., 1%.
In operation, according to one embodiment, the mobile communication device 200 can receive a radio frequency signal for a frame. For example, the mobile communication device 200 can receive a frame on a forward dedicated control channel. The mobile communication device 200 can perform demodulation on the signal to obtain a scrambled signal. The mobile communication device 200 can then extract a unique identifier from the scrambled signal. The unique identifier can be extracted at any point during or after the process of receiving a signal, a frame, or the like. The unique identifier can be a group identifier that identifies at least one mobile communication device for which the signal is intended, a mobile station identity that identifies a specific mobile communication device for which the signal is intended, or any other unique identifier. Also, the unique identifier can be obtained from a power control section of the scrambled signal or from any other portion of the signal. The mobile communication device 200 can then examine the unique identifier extracted from the scrambled signal to determine if the signal is intended for the mobile communication device 100.
The mobile communication device 200 can also descramble the scrambled signal using a long code mask to obtain a channel encoded signal, channel decode the channel coded signal to obtain a cyclic redundancy coded signal, cyclic redundancy code check the cyclic redundancy coded signal, determine if the cyclic redundancy coded signal fails the cyclic redundancy code check, and increase a received Eb/Nt set point if in the examining step it is determined that the signal is intended for the mobile communication device but the cyclic redundancy coded signal fails the cyclic redundancy code check. Further, the mobile communication device can decrease a received Eb/Nt set point if in examining it is determined that the signal is intended for the mobile communications device but the cyclic redundancy coded signals pass the cyclic redundancy code check.
After extracting the unique identifier, the mobile communication device 200 can additionally descramble the scrambled signal to obtain a channel encoded signal and channel decode the channel encoded signal to obtain a cyclic redundancy coded signal.
According to another related embodiment, the mobile communication device 200 can receive a radio frequency signal for a frame, perform demodulation on the signal to obtain a scrambled signal, descramble the scrambled signal to obtain a channel encoded signal, channel decode the channel encoded signal to obtain a cyclic redundancy coded signal, cyclic redundancy code check the cyclic redundancy coded signal, and if the cyclic redundancy coded signal fails the cyclic redundancy code check, examine a unique identifier to determine if the signal is intended for the mobile communication device 200. The mobile communication device 200 can receive the radio frequency signal for a frame on a forward dedicated control channel. Also, the unique identifier can be a group identifier that identifies at least one mobile communication device for which the signal is intended or a mobile station identity that identifies a specific mobile communication device for which the signal is intended. The unique identifier can be obtained from a power control section or any portion of the scrambled signal. The mobile communication device 200 can further attempt to descramble the scrambled signal using a long code mask, determine the scrambled signal is unsuccessfully descrambled, and increase a received Eb/Nt set point if in the examining step it is determined that the signal is intended for the mobile communication device but the scrambled signal is unsuccessfully descrambled. Additionally, the radio frequency signal can be received on a forward dedicated control channel.
The frame determination module 290 can additionally include a power controller 550. Thus, the descrambler 520 can attempt to descramble the scrambled signal using a long code mask and determine the scrambled signal is unsuccessfully descrambled. The power controller 550 can then increase a transmission, reception, or transceiver power set point if it is determined that the signal is intended for the mobile communication device 200 but the scrambled signal is unsuccessfully descrambled. The power controller can also decrease the Eb/Nt set point if it is determined that the signal is intended for the mobile communications device and the scrambled signal is successfully descrambled.
The method of this invention is preferably implemented on a programmed processor. However, the network controller 140, the controller 220, and/or the frame determination module 290 may also be implemented on a general purpose or special purpose computer, a programmed microprocessor or microcontroller and peripheral integrated circuit elements, an ASIC or other integrated circuit, a hardware electronic or logic circuit such as a discrete element circuit, a programmable logic device such as a PLD, PLA, FPGA or PAL, or the like. In general, any device on which resides a finite state machine capable of implementing the flowcharts shown in the Figures may be used to implement the processor functions of this invention.
While this invention has been described with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. For example, various components of the embodiments may be interchanged, added, or substituted in the other embodiments. Also, all of the elements of each figure are not necessary for operation of the disclosed embodiments. For example, one of ordinary skill in the art of the disclosed embodiments would be enabled to make and use the invention by simply employing the elements of the independent claims. Accordingly, the preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention.
