Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B7/00—Radio transmission systems, i.e. using radiation field
  • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
  • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
  • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W16/00—Network planning, e.g. coverage or traffic planning tools; Network deployment, e.g. resource partitioning or cells structures
  • H04W16/24—Cell structures
  • H04W16/28—Cell structures using beam steering

Definitions

• the present invention applies generally to signal processing in radio communication systems, and more particularly to the detection and correction of a channel swap in a spatial division multiple access system.
• Radio communication systems may have a cellular architecture, with each cell corresponding roughly to a geographical area.
• Each cell includes a base station (BS), which is a local central cite through which a number of radio transmitter/receiver units (user terminals (UTs)) gain access to the communications system.
• the UTs could be, for example, telephones, PDAs, or small modem boards.
• a UT establishes a communication link with other UTs by requesting access to the system through the BS.
• Each UT communicates over a communication channel distinguished from other UTs.
• TDMA Time division multiple access
• Radio communications systems may employ a spatial division multiple access (SDMA) scheme, in conjunction with one or more conventional multiple access schemes, to increase the number of UTs that a BS can serve for a given number of available frequencies.
• SDMA spatial division multiple access
• An SDMA scheme may be implemented using a BS that has an array of receiver and/or transmitter antenna elements. The antenna elements are spaced, one from another, and may be positioned in various configurations. The array of antenna elements introduces a spatial dimension that can be used to differentiate two or more UTs concurrently accessing a given conventional channel. That is, the basis of an SDMA system is that the BS creates a spatially distinct SDMA channel for each of multiple users even though they share the same carrier frequency (FDMA), timeslot
• FDMA carrier frequency
• TDMA time division multiple access
• CDMA spreading code
• Channel swap may occur where the spatial processing capability of the
• Channel swap may also be the result of an unstable communication signal of one or more of the UTs.
• channel swap may also occur when one or more SDMA channels experiences deep fading and communication with the BS is interrupted. Upon resuming communication, the communication link between each UT may be swapped.
• Channel swap is not detectable by either the UTs or the BS. This is because only the data streams are from different UTs.
• the swapped signals appear identical in terms of physical characteristics such as bit structure, coding, and cyclic redundancy check (CRC), among others.
• Channel swap can have serious detrimental consequences.
• Channel swap may cause the users at each UT to become involved in unintended communications.
• each UT will be employing an erroneous encryption key.
• the result will be that each user may receive only annoying "white” noise during a channel swap for such systems.
• Embodiments of the invention provide various methods for detecting a spatial division multiple access (SDMA) channel swap.
• SDMA spatial division multiple access
• a first SDMA communication channel is assigned to a first user terminal that initially transmits its signal over the first SDMA communication channel.
• a second SDMA communication channel is assigned to a second user terminal that initially transmits its signal over the second SDMA communication channel.
• the first user terminal's signal and the second user terminal's signal are analyzed to determine that the first user terminal is transmitting its signal over the second SDMA communication channel and the second user terminal is transmitting its signal over the first SDMA communication channel.
• Figure 1 illustrates a process in which an SDMA communication channel swap is detected and corrected in accordance with one embodiment of the invention
• Figure 2 illustrates an exemplary cellular radio communications network providing SDMA channel swap detection and correction functionality in accordance with an embodiment of the invention
• Figure 3 illustrates a process in which a proscribed value in the data stream is used in conjunction with a CRC to detect the occurrence of an SDMA channel swap
• Figure 4 illustrates a process in which one or more physical characteristics of the UTs' signal are used to detect the occurrence of an SDMA channel swap
• Figure 5 illustrates a process in which independent error detection processes implemented at each of multiple communication layers are used to detect the occurrence of an SDMA channel swap.
• Embodiments of the invention provide methods for detecting an SDMA channel swap by periodically analyzing the signal from two or more UTs having spatially distinct channels.
• the signals from each UT are encoded using an encoding scheme that has invalid (illegal) outputs.
• the data stream of the signal contains an invalid output, and the CRC does not indicate an error in the communication link, a channel swap is indicated.
• certain physical characteristics of the signals are analyzed to determine a channel swap.
• the results of error detection processes for different communication layers are compared to determine a channel swap.
• FIG. 1 illustrates a process in which an SDMA communication channel swap is detected and corrected in accordance with one embodiment of the invention.
• Process 100 begins with operation 105 in which each of two UTs is assigned a spatially distinct communication channel. Depending on the air interface used (e.g., FDMA, TDMA, or CDMA), these communication channels may have the same carrier frequency, timeslot, or spreading code.
• Each UT uses its assigned SDMA communication channel to transmit its signal to communicate with the corresponding base station.
• the signal received from one or both UTs is analyzed at the base station.
• Various forms of analysis may be used separately or in conjunction with one another.
• FIG. 2 illustrates an exemplary cellular radio communications network providing SDMA channel swap detection and correction functionality in accordance with an embodiment of the invention.
• Network 200 shown in Figure 2, includes a plurality of BSs shown as BS 206A and 206B.
• the BSs couple to base station controllers (BSCs), shown as BSCs 204A and 204B, with each BSC serving a plurality of BSs.
• BSCs base station controllers
• the BSCs also couple to a mobile switching center (MSC) 202 that may interface other MSCs and the Public Switched Telephone Network (PSTN).
• MSC mobile switching center
• PSTN Public Switched Telephone Network
• UTs 208A1 and 208A2, being serviced by BS 206A are operating normally. That is, UT 208A1 is communicating data over its assigned SDMA channel, namely SDMA channel Al, and UT 208 A2 is communicating data over its assigned SDMA channel, namely SDMA channel A2.
• UTs 208B1 and 208B2, being serviced by BS 206B have experienced an SDMA channel swap. That is, UT 208B1 is communicating data over the SDMA channel assigned to UT 208B2, namely SDMA channel B2, and UT 208B2 is communicating data over the SDMA channel assigned to UT 208B1, namely SDMA channel Bl.
• each base station 206 A and 206B contains SDMA channel swap detection functionality, labeled 209A and 209B respectively, which may include software, hardware, or a combination thereof.
• the MSC 202, and each BSC, 204A and 204B may contain such functionality, shown as 210-212, respectively.
• the SDMA channel swap detection functionality effects the operations discussed above in reference to Figure 1 and described, in alternative embodiments, in more detail below.
• Some systems employ an encoding scheme that has proscribed output values for the data stream and also employ a scrambling code.
• PHS Personal Handyphone System
• ADPCM adaptive differential pulse code modulation
• an output that contains a 0 bit is an illegal output. That is, the data stream from the encoder will not contain a 0 bit during normal operation.
• an SDMA channel swap occurs, the wrong scramble sequence will be used for de- scrambling. The result is that 0 frequently appears in the swapped channel data stream. This can be used to detect an SDMA channel swap.
• the data stream contains a 0 bit, it typically indicates one of two circumstances; either the communication link is defective or an SDMA channel swap has occurred. To eliminate the possibility of a defective communication link, the CRC is examined.
• Figure 3 illustrates a process in which a proscribed value in the data stream is used in conjunction with a CRC to detect the occurrence of an SDMA channel swap.
• Process 300 begins at operation 305 in which the encoded (e.g., ADPCM encoded) data stream is examined for proscribed outputs.
• the encoded e.g., ADPCM encoded
• the data stream is examined again periodically (e.g., every data burst). If, at operation 310, the data stream does contain a proscribed output, then the process continues at operation 315 to determine the cause of the proscribed output.
• the CRC is evaluated to determine if the CRC indicates a communication link error. If the CRC indicates a communication link error, then this is determined to be the cause of the proscribed output in the data stream. The communication link error is then addressed at operation 316. If the CRC indicates that no communication link error has occurred, then at operation 320 the cause of the proscribed output in the data stream is determined to be an SDMA channel swap. At this point the data streams of each UT may be interchanged at the BS to effect correction of the SDMA channel swap as discussed above. In an alternative embodiment, further data bursts may be evaluated prior to making a determination of SDMA channel swap, in order to increase the reliability of the determination.
• Evaluation of the data stream to determine if proscribed outputs occur is a highly reliable and efficient method for determining that an SDMA channel swap has occurred.
• the method is applicable to systems employing an encoding scheme that has proscribed data stream outputs.
• Alternative embodiments of the invention provide methods for systems that do not necessarily employ such encoding schemes.
• the physical characteristics of each of two SDMA signals can be used to distinguish them.
• the BS that services the UTs is not only aware of each SDMA channel and link that has been established, but is also aware of the physical characteristics of the signal from each UT and maintains a history of one or more of these characteristics.
• the ability to distinguish the signals can be used to effect determination of an SDMA channel swap. For example there may be a sudden interchange of physical characteristics between two UTs in the event of an SDMA channel swap or the physical characteristics may indicate an SDMA channel swap in other ways.
• the physical characteristics that could be used for such a determination are numerous, but would not include those characteristics that would be the same for two SDMA channels (e.g., frequency or timeslot). Several exemplary physical characteristics are discussed below. Frequency Offset
• the local oscillator at each UT typically has a slight, but distinct frequency deviation from the established carrier frequency.
• two UTs may be assigned a common carrier frequency of 1.895 MHz, where one UT is actually using 1.8953 MHz and the other is using 1.8957 MHz. This deviation from the assigned frequency may be due to frequency instability or hardware tolerances or imperfections. TIME OF ARRIVAL AT THE BS
• the signal from each UT will have a different time of arrival as measured at the BS. That is, the BS has the capability of determining the time from transmission of a signal to reception at the BS. These times will typically vary for two UTs.
• the signal of each UT will exhibit a distinct spatial signature.
• the spatial signatures of each signal are dependent upon the particular location of the UT and the
• EVM Error vector magnitude
• the signal from the UT may exhibit specific characteristics during spectral analysis. For example, in such cases the
• UTs signal may produce a noise-like spectrum.
• Figure 4 illustrates a process in which one or more physical characteristics of the UTs' signal are used to detect the occurrence of an SDMA channel swap.
• Process 400 begins at operation 405 in which particular physical characteristics of the UT signal are selected for SDMA channel swap detection analysis. Certain physical characteristics may be better suited to a particular system.
• time-of-arrival may be more suitable than for a system employing an air interface having a narrower band
• the one or more physical characteristics of the UT signal selected in operation 405 are analyzed.
• This analysis may include a comparison of the selected characteristic of the currently received signal with a history of the physical characteristic maintained at the BS for the particular channel. That is, for various embodiments the BS may maintain a history of one or more physical characteristics of the UT signal received on each SDMA channel. At the time of analysis, the currently received value of the UT signal is compared with these histories.
• the analysis may be restricted to the currently received UT signal. For example as noted above, the signal spectrum of a UT signal received over a swapped SDMA channel exhibits indicative characteristics.
• the analysis of operation 410 is used to make a determination of whether an SDMA channel swap has occurred. For example, if the physical characteristics of the currently received signal for a UT communicating over a particular SDMA channel more closely match the maintained history of the physical characteristics of the signal of a UT communicating over a different SDMA channel, then a determination that an SDMA channel swap has occurred is warranted. Again, such analysis may be repeated to increase the reliability of such determination. Additionally, any number of appropriate physical characteristics may be analyzed. INCONSISTENT ERROR DETECTION METHOD
• Data is typically communicated over several protocol layers of a hierarchy of layers. Each layer uses the layer immediately below it and provides a service to the layer above.
• the typically lowest protocol layer is the physical layer that supports the electrical or mechanical interface to the physical medium.
• the physical layer determines the physical data stream structure for the layer above it (i.e., the data- link layer).
• the data-link layer is responsible for fragmenting data (e.g., dividing data into frames) for transmission on the physical layer.
• error detection process e.g., a CRC
• CRC error detection process
• Many systems implement an independent error detection process at one or more additional layers. For example, in a PHS system, when the PHS Internet Access Forum Standard (PIAFS) is used, there is an additional error detection process, across different physical layer frames, implemented at the data-linlc layer. Usually, the results of the error detection process at each layer are not communicated to the other layers.
• PAFS PHS Internet Access Forum Standard
• Such independent error detection processes implemented at different layers may be used to detect an SDMA channel swap.
• SDMA channel swap may have occurred.
• the SDMA channel may be corrected in the physical layer, or in any layers above it (e.g., data-link layer, network layer, etc.)
• Figure 5 illustrates a process in which independent error detection processes implemented at each of multiple communication layers are used to detect the occurrence of an SDMA channel swap.
• Process 500 shown in Figure 5, begins at operation 505 in which an error detection process is performed at the physical layer.
• a properly designed SDMA system should be able to detect an SDMA channel swap and effect correction "gracefully.”
• Embodiments of the invention may be applied to detect and correct an SDMA channel swap.
• the foregoing methods may be used separately or in conjunction with one another, as appropriate, to increase reliability in determining if an SDMA channel swap has occurred.
• the SDMA channel swap detection process may be repeated during the entire communication period, for example one or more methods may be performed at every data burst. In alternative embodiments, the SDMA channel swap detection process may be accomplished at a BS, a BSC, an MSC, or a combination of these control devices. [0056] Upon detection of an SDMA channel swap, the BS or other control device effects correction by interchanging the data streams received over each SDMA channel, for both uplink and downlink. That is, the BS ascribes the UT data stream received over one SDMA channel to the other SDMA channel.
• the invention includes various operations.
• the operations of the invention may be performed by hardware components or may be embodied in machine- executable instructions, which may be used to cause a general-purpose or special- purpose processor or logic circuits programmed with the instructions to perform the operations. Alternatively, the operations may be performed by a combination of hardware and software.
• the invention may be provided as a computer program product that may include a machine-readable medium having stored thereon instructions, which may be used to program a computer (or other electronic devices) to perform a process according to the invention.
• the machine-readable medium may include, but is not limited to, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, flash memory, or other type of media/machine-readable medium suitable for storing electronic instructions.
• the invention may also be downloaded as a computer program product, wherein the program may be transferred from a remote computer to a requesting computer by way of data signals embodied in a carrier wave or other propagation medium via a communication cell (e.g., a modem or network connection).
• the operations may be performed at a BS, a BSC, a MSC, or performed by a combination of these control devices.
• Embodiments have been herein described in the context of ,a cellular radio communication system, but alternative embodiments may be applied to a wide variety of different systems in which data are exchanged. Such systems include voice, video, music, broadcast and other types of data systems without external connections. Many of the methods are described in their most basic form but operations can be added to or deleted from any of the methods without departing from the basic scope of the invention. [0060] While the invention has been described in terms of several embodiments, those skilled in the art will recognize that the invention is not limited to the embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.

Landscapes

• Engineering & Computer Science (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Mobile Radio Communication Systems (AREA)
• Radio Transmission System (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (2)

Family

ID=32654553

Family Applications (1)

Country Status (5)

Families Citing this family (10)

Family Cites Families (9)

• 2002
  • 2002-12-27 US US10/330,639 patent/US6894993B2/en not_active Expired - Lifetime
• 2003
  • 2003-12-24 AU AU2003297532A patent/AU2003297532A1/en not_active Abandoned
  • 2003-12-24 JP JP2004565698A patent/JP4563819B2/ja not_active Expired - Fee Related
  • 2003-12-24 WO PCT/US2003/041250 patent/WO2004062301A2/en not_active Ceased
  • 2003-12-24 CN CNA200380109795XA patent/CN1748432A/zh active Pending

Also Published As

Similar Documents

Legal Events