EP1374423A2 - Systeme et procede de communication a acces multiple par repartition de code sans fil - Google Patents

Systeme et procede de communication a acces multiple par repartition de code sans fil

Info

Publication number
EP1374423A2
EP1374423A2 EP02712200A EP02712200A EP1374423A2 EP 1374423 A2 EP1374423 A2 EP 1374423A2 EP 02712200 A EP02712200 A EP 02712200A EP 02712200 A EP02712200 A EP 02712200A EP 1374423 A2 EP1374423 A2 EP 1374423A2
Authority
EP
European Patent Office
Prior art keywords
multiple access
division multiple
base station
code division
code
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP02712200A
Other languages
German (de)
English (en)
Inventor
Bassam M. Hashem
Eman A. Fituri
Mark Earnshaw
Shalini S. Periyalwar
Leo L. Strawczynski
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Nortel Networks Ltd
Original Assignee
Nortel Networks Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US09/797,273 external-priority patent/US6930470B2/en
Application filed by Nortel Networks Ltd filed Critical Nortel Networks Ltd
Publication of EP1374423A2 publication Critical patent/EP1374423A2/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/04—Wireless resource allocation
    • H04W72/044—Wireless resource allocation based on the type of the allocated resource
    • H04W72/0446—Resources in time domain, e.g. slots or frames
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/0007—Code type
    • H04J13/0022—PN, e.g. Kronecker
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J13/00—Code division multiplex systems
    • H04J13/16—Code allocation
    • H04J13/18—Allocation of orthogonal codes
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W36/00—Hand-off or reselection arrangements
    • H04W36/16—Performing reselection for specific purposes
    • H04W36/18—Performing reselection for specific purposes for allowing seamless reselection, e.g. soft reselection
    • H04W36/185—Performing reselection for specific purposes for allowing seamless reselection, e.g. soft reselection using make before break

Definitions

  • the present invention relates to a system and method for wireless communication for a reverse communication link (wireless device to base station), and in particular, to a system and method for wireless communication in code division multiple access (CDMA) environment which assigns communication time slots and/or spreading codes for asynchronous operation and synchronous operation based on one or more performance characteristics.
  • CDMA code division multiple access
  • wireless communication devices also include personal digital assistants (PDAs), pagers, network appliances, laptop and desktop computers, etc.
  • PDAs personal digital assistants
  • These devices and their users can be divided into three categories, namely, mobile, nomadic and stationary.
  • Mobile devices refer to devices which are moving during use, such as telephones and personal digital assistants when used while walking, riding in a vehicle, and the like.
  • Stationary devices refer to devices which are typically not prone to movement, even during repeated use.
  • An example of a stationary device is a personal tower computer equipped with wireless communication capability.
  • Nomadic devices refer to devices which can move from place to place but are typically stationary during use. Although typically stationary during use, a nomadic device can also be mobile during use.
  • An example of a nomadic device is a laptop computer equipped with wireless communication capability in which the laptop computer is used in an office and moved to another location for subsequent use. According to this example, the laptop computer can be used while being moved, such as while riding in a train or car.
  • Current wireless communication infrastructures also include one or more base stations, used to communicate with the wireless devices, arranged in a network with access being provided to external services, for example, Internet access.
  • Demand is such that the infrastructure exists in the form of increasing base station and antenna densities, as well as increasing processing loads placed on base station communication equipment as devices are added to the system.
  • CDMA environments such as the 3GPP propose two types of reverse link designs, namely, synchronous code division multiple access (SCDMA) and asynchronous code division multiple access (ACDMA) with devices operating on one or the other type of link.
  • SCDMA synchronous code division multiple access
  • ACDMA asynchronous code division multiple access
  • the 3GPP does not address the complementary use of SCDMA codes and ACDMA codes on the reverse link.
  • neither the 3GPP nor the CDMA2000 communication environment address the complementary use of SCDMA codes and ACMDA codes based on the type of device, i.e. stationary or mobile.
  • SCDMA refers to synchronous orthogonal transmission in which each communication channel is identified by a different orthogonal spreading sequence, and synchronization among channels is achieved by ensuring that transmissions arrive at each receiver at substantially the same time.
  • an ACDMA link is a link in which transmissions arrive at the receivers at different times. ACDMA links result in a loss in the orthogonality ofthe system and an increase in interference within each base station's coverage area, i.e. cell, as compared with a SCDMA link.
  • Soft handover refers to the simultaneous communication between a wireless device and multiple base stations such that communication is transferred from one base station to another in a make-before-break fashion, i.e., communication is established with the new base station prior to breaking the communication link with the current base station.
  • a device using an SCDMA code can maintain soft handoff with other base stations, however, these other base stations see the SCDMA code as an ordinary pseudo-noise code. Therefore, devices in soft handoff increase the amount of interference experienced by the SCDMA devices within the cell. Because accurate time alignment, e.g. within one-eighth or one-quarter of a chip, is required in a high- capacity SCDMA system, devices in the mobile category described above have difficulty maintaining synchronous operation on the reverse link due to device movement with respect to other devices and the base station. Furthermore, the ability to maintain synchronization is also impacted by the variability in fading and interference, even for stationary uses. This adverse effect is particularly prevalent in wide-band (i.e. 5 MHz and up) systems due to the very fast chip rates involved. As a result, systems such as those conforming to 3GPP standards propose separate designs for low and high mobility devices.
  • the category in which a device operates may change, for example, when a mobile device user stops moving for a prolonged period.
  • Current systems do not, however, support the switch between one category and another, i.e., ACDMA to/from SCDMA reverse link operation.
  • a mobile device which becomes stationary may be relegated to less efficient and lower capacity asynchronous operation when, in fact, the device could make efficient use of an SCDMA reverse link.
  • a nomadic device which changes from stationary to mobile operation may adversely impact the performance of an originally assigned SCDMA reverse link due to its imposition of increased channel interference due to the inability to maintain orthogonality.
  • RRMs radio resource managers
  • schedulers operate to manage the wireless communication channels for a base station or group of base stations by assigning time slots, frequencies and spreading codes to the wireless devices associated with the base station(s). These assignments are typically based on channel conditions such as channel quality (C/I ratio), but can also be assigned based on quality of service requirements, wireless device communication priority and/or a round robin assignment scheme.
  • C/I ratio channel quality
  • a time slot represents the unit of time which serves to divide the sharing of transmission resources in the time domain. Typically, such time slots are quite short, for example, on the order of one millisecond.
  • a device may be granted transmission resources for one or more consecutive time slots. After this time period has passed, another device may be granted the same transmission resources. However, the transmissions from the two devices are separated in time because they are transmitting in separate time slots. As such the devices do not interfere with each other.
  • RRMs do not include support for tracking whether time slots are allocated to spreading codes for ACDMA or SCDMA communication.
  • Known RRMs also cannot group wireless devices into those using/requiring ADCMA communication, i.e. wireless devices not in orthogonal communication with other wireless devices and those wireless devices using/requiring SCDMA communication, i.e. wireless devices in orthogonal communication with other wireless devices, in order to facilitate time slot assignment which maximizes channel capacity.
  • time slots associated with a particular channel are assigned in a non-optimal fashion, thereby leading to inefficient use ofthe channel and a reduction in channel and system capacity.
  • the present invention advantageously provides radio resource manager functions which expand the number of orthogonal codes available within a cell by allowing code reuse and by assigning time slots to groups of devices which can benefit from the use of SCDMA codes.
  • a method provided by the present invention advantageously allows the use of a single large bandwidth carrier to support ACDMA and SCDMA codes, thereby avoiding the need to support multiple carriers with guard bands there between.
  • the present invention provides a method of assigning a time slot for wireless communication between a device and a base station in which one or more performance characteristics corresponding to the device are determined. A spreading code based on the determined performance characteristics is assigned. A time slot for communication with the base station is assigned based on the assigned spreading code.
  • the present invention provides an apparatus for assigning a time slot for wireless communication between a device and a base station, in which the apparatus has a central processing unit.
  • the central processing unit operates to determine one or more performance characteristics corresponding to the device, assign a spreading code based on the determined performance characteristics and assign a time slot for communication with the base station based on the assigned spreading code.
  • the present invention provides a communication signal embodied in a wireless communication medium between a device and a base station.
  • the wireless signal has a plurality of time slots in which each ofthe plurality of time slots supports communication from the device to the base station using one of synchronous code division multiple access codes and asynchronous code division multiple access codes.
  • the present invention provides a method of selecting spreading code sets associated with code division multiple access wireless communication between a device and a base station in which a scrambling code is selected from a plurality of scrambling codes corresponding to the base station.
  • a code division multiple access spreading code set is selected from a plurality of code division multiple access spreading code sets corresponding to the base station such that a first combination of a first spreading code set with a scrambling code yields total codes which are orthogonal to a second combination of a second spreading code set with the scrambling code.
  • the present invention advantageously provides a system and method which allows a device and a base station wirelessly communicate with each other using a carrier and reverse link coding technique optimized based on the operational profile of the device.
  • devices which are stationary can use an SCDMA link
  • mobile devices can use an ACDMA link.
  • the present invention is arranged such that the synchronization ofthe device and base station is monitored and, if a change in mobility is detected, such as stationary to mobile operation, communication is switched from the current carrier to a carrier employing a link whose CDMA code is suitable to the changed mobility state.
  • a method of using a code division multiple access carrier for wireless communication between a device and a base station in which an operational profile ofthe device is determined.
  • the operational profile includes a degree of unit mobility.
  • a first carrier for wireless code division multiple access communication from the device to the base station is selected based on the determined operational profile ofthe device.
  • a wireless communication link between the device and the base station is established using the first carrier.
  • the present invention provides device using at least one code division multiple access carrier for wireless communication with a base station, in which the device has a transmitter and a central processing unit in operative communication with the transmitter.
  • the transmitter transmits a first signal to the base station using a first designated carrier.
  • the central processing unit determines an operational profile, selects the first designated carrier based on the determined operational profile and establishes a wireless communication link with the base station using the first designated carrier.
  • the operational profile includes a degree of unit mobility
  • the present invention provides a wireless signal for communication between a device and a base station in which the wireless signal has a plurality of carriers.
  • Each ofthe plurality of carriers provides a synchronous code division multiple access communication link or an asynchronous code division multiple access communication link.
  • Each carrier providing the synchronous code division multiple access communication link is used by a stationary wireless device and each carrier providing the asynchronous code division multiple access communication link is used by a mobile wireless device.
  • the present invention provides a base station which uses at least one code division multiple access carrier for receiving wireless communication from a device in which the base station has a receiver and a central processing unit in operative communication with the receiver.
  • the central processing unit determines an operational profile ofthe device, selects a first designated carrier based on the determined operational profile and establishes a wireless communication link with the device using the first designated carrier.
  • the operational profile includes a degree of unit mobility.
  • the receiver receives a first signal from the device using the first designated carrier.
  • FIG. 1 is a block diagram of a communication system constructed in accordance with the principles ofthe present invention
  • FIG. 2 is a diagram of an arrangement of a multi-carrier system constructed in accordance with the principles ofthe present invention
  • FIG. 3 is a block diagram ofthe wireless communication section of a device constructed in accordance with the principles ofthe present invention.
  • FIG. 4 is a block diagram ofthe wireless communication section of a base station constructed in accordance with the principles ofthe present invention.
  • FIG. 5 is a flowchart ofthe overall operation ofthe system and the communication units
  • FIG. 6 is a flowchart ofthe new carrier selection process
  • FIG. 7 is a diagram of an alternative hardware arrangement constructed in accordance with the principles ofthe present invention.
  • FIG. 8 is a diagram of a cell showing exemplary total code arrangements in accordance with the principles ofthe present invention.
  • FIG. 9 is a diagram of a time slot arrangement of a communication channel
  • FIG. 10 is a table of an exemplary time slot assignment
  • FIG. 1 a communication system constructed in accordance with the principles ofthe present invention and designated generally as 10.
  • Communication system 10 preferably includes one or more wireless devices 12 (shown as handheld wireless device 12a, wireless tower computer 12b, wireless vehicular mounted phone 12c, and wireless laptop computer 12d) in communication with one or more base stations 14 via wireless communication network 16.
  • Devices 12 and base stations 14 are commonly referred to together herein as "units”.
  • Handheld wireless device 12a is an example of a mobile device
  • wireless tower 12b is an example of a stationary device
  • vehicular mounted wireless phone 12c is an example of a mobile device
  • wireless laptop computer 12d is an example of a nomadic device.
  • handheld wireless device 12a and vehicular mounted wireless phone 12c may also be considered nomadic devices because they are operable when the user (or vehicle) is stationary as well as when the user (or vehicle) is moving.
  • devices 12a and 12c are considered mobile as discussed herein, because these devices are typically in motion when being used.
  • Communication system 10 is also comprised of base station communication network 18 coupled to base stations 14 via communication links 20.
  • Communication links 20 and communication network 18 can undertake any arrangement used to facilitate communication between base stations 14 themselves and/or external services such as Internet access, news and stock quotation services and the like (not shown). Arrangements for communication network 18 and communication links 20 such as those used to support digital wireless networks are known. For example, communication links 20 can be wireless or wired links such as multi-megabit per second links. Communication network 18 is comprised of digital switches, routers and other known digital communication devices.
  • Devices 12 are any wireless communication devices, and are not limited solely to the four types of devices shown in FIG. 1. Each of devices 12 includes a wireless communication section, described below in detail, which receives and transmits wireless communication signals to and from base stations 14.
  • Wireless communication network 16 is preferably a wideband system.
  • the term "wideband" refers to systems having a minimum of a 5 MHz bandwidth.
  • the wideband system is preferably arranged as a multi-carrier system in which wireless communication links between devices 12 and/or base stations 14 are established using one ofthe carriers in the multi-carrier system.
  • FIG. 2 shows a diagram of an arrangement of a multi-carrier system for reverse links constructed in accordance with the principles ofthe present invention.
  • multi- carrier system 22 is comprised of a plurality of carriers, namely, carrier A 24a, carrier B 24b and carrier C 24c.
  • FIG. 2 shows adjacent carriers, the present invention is not limited to such.
  • multi-carrier system 22 can be arranged as a 5 MHz system in which each of carriers A-C (24a, 24b and 24c) are 1.25 MHz carrier channels.
  • carriers A-C 24a, 24b and 24c
  • individual carriers are used to support particular link arrangements suited to the particular characteristics to the devices using the carrier, for example, ACDMA and SCDMA wireless communication links.
  • carrier A 24a can be used to support an ACDMA reverse link while carrier B 24b can be used to support an SCDMA reverse link.
  • wireless communication network 16 can be included as part of any wireless communication system, including a wireless high speed fixed access data system employing a wireless Highspeed Data Protocol (HDP) or a wireless Digital Subscriber Line (DSL) signal. Further, it is contemplated that wireless communication network 16 can be included as part of a wireless local area network. Standardized protocols for providing a wireless high speed data protocol, a wireless DSL signal and a wireless local area network signal are known. As used herein, the term "protocol" refers to the arrangement of data within a data packet, such as packet headers, footers, packet size, etc.
  • FIG. 3 is a block diagram ofthe wireless communication portion of a device 12 constructed in accordance with the principles ofthe present invention.
  • the wireless communication portion of device 12 preferably includes a device receiver 26 and a device transmitter 28, each of which are coupled to and controlled by device central processing unit 30.
  • Device receiver 26 and device transmitter 28 are coupled to antenna 32 for respectively receiving and transmitting signals to and from other units.
  • Device receiver 26 is preferably arranged to receive signals transmitted by base station 14.
  • Device transmitter 28 is preferably arranged to transmit CDMA spread spectrum signals, such as ACDMA and SCDMA spread spectrum signals, to base station 14 via antenna 32.
  • Device central processing unit 30 is any central processing unit capable of executing the device functions described in detail below.
  • device central processing unit 30 is preferably arranged to include or have access to sufficient memory (not shown) required to store data, buffer, transmit and receive data and programmatic code to perform its designated, below-described functions. Further, device central processing unit 30 is preferably arranged to cause device 12 to switch between carriers in a multi- carrier system. This is the case regardless of whether device 12 determines that the carrier switch is necessary or whether the carrier switch is executed based on an instruction received from another unit such as base station 14.
  • Devices 12 are operable to communicate with base station 14 using SCDMA or ACDMA communication on the reverse link, depending upon the operational profile ofthe device, and are operable to switch between ACDMA and SCDMA communication links using suitable carrier handoff protocols typically used to change carriers in multi-carrier wireless communications.
  • FIG. 4 is a block diagram of a base station 14 constructed in accordance with the principles ofthe present invention.
  • base station 14 is preferably comprised of base station receiver 34 and base station transmitter 36, each of which are coupled to and controlled by base station central processing unit 38.
  • Base station 14 is also preferably comprised of base station antenna subsystem 40 which is coupled to base station receiver 34 and base station transmitter 36 for receiving signals transmitted by device 12 and transmitting signals to device 12, respectively.
  • Base station 14 preferably also includes base station link 42 which provides the necessary interface hardware and/or software to couple base station 14 to communication network 18 via communication link 20.
  • This interface hardware takes the form of plugs, jacks and electronic circuit elements.
  • the interface software when executed, provides the drivers and other functions necessary to receive data from communication network 18 and transmit data to communication network 18.
  • Base station receiver 34 is preferably arranged to receive wireless spread spectrum CDMA signals, such as ACDMA and SCDMA signals, from a plurality of devices 12. Further, base stations 14 transmit time alignment commands to devices 12 to instruct devices 12 to adjust their transmit timing to maintain synchronous alignment during transmission. Techniques for determining and transmitting time alignment commands in a wireless communication environment are known.
  • Base station central processing unit 38 preferably includes or has access to a storage unit which contains the programmatic instructions needed to perform the below-described functions. Further, the storage unit is preferably arranged to store data corresponding to in-progress communication with devices 12, provide buffering of data transmitted and/or received to/from devices 12 and communication network 18, and the like. In general, any central processing unit which provides the described functions of base station 14 can be used.
  • each ofthe above- described elements of the respective devices are arranged with a communication structure which facilitates communication among the respective elements. Further, it is contemplated that any combination ofthe elements of each respective device 12 and base station 14, such as the receivers, transmitters and central processing units, can be provided as a single semi-conductor integrated circuit.
  • each base station 14 is equipped with the ability to communicate with devices 12 using one or a combination of a plurality of carriers in a multi-carrier environment. Further, each base station 14 operates to determine whether to communicate with devices 12 via an ACDMA link or an SCDMA link, in particular the reverse link, based on one or more operational profile characteristics. These characteristics include whether the device is mobile or stationary and whether there are sufficient orthogonal spreading codes available for SCDMA operation.
  • the operational profile of device 12 is determined (step SI 00), preferably by base station 14.
  • the operational profile includes a characteristic indicating the degree of mobility ofthe device.
  • the degree of mobility can take the form of a binary determination, such as stationary or mobile, or the specific degree of mobility can be determined and included as part ofthe operational profile.
  • Techniques for determining the specific degree of mobility by estimating the velocity of a mobile device 12 based on variations in the timing ofthe received signal at base station 14 are known.
  • the access channel or a signaling channel on either an SCDMA carrier or an ACDMA carrier can be used for estimating the velocity.
  • Base stations 14 estimate the degree of mobility of device 12 by tracking the frequency of time alignment changes transmitted to a device 12.
  • the degree of mobility can be set as stationary if mobility is less than a predetermined value, or as mobile if mobility is greater than a predetermined value.
  • the predetermined value is preferably based on the chip rate and the resultant ability of base station 14 to maintain SCDMA links with devices 12.
  • device 12 can determine its own degree of mobility and provide this determination to base station 14.
  • device 12 may be equipped with a tracking system such as a global positioning receiver which determines the change in position of device 12 overtime, i.e. velocity.
  • a carrier for the communication link between device 12 and base station 14 is selected based, at least in part, on the operational profile (step S102).
  • a carrier is selected by base station 14 from among carriers in a multi-carrier environment which are dedicated to SCDMA spread spectrum communication links and ACDMA spread spectrum communication links. It is contemplated that device 12 can also select the carrier The carrier selection process is discussed in detail below.
  • a communication link is established using the selected carrier (step SI 04) and data communication between device 12 and base station 14 commenced using the selected carrier (step SI 06).
  • Communication links established as ACDMA communication links proceed using those facilities provided by the system for ACDMA communication.
  • a system supporting mobile devices on a carrier supporting ACDMA communication links may employ "soft handover" techniques between a mobile device 12, such as wireless vehicular mounted phone 12c, and multiple base stations 14.
  • Data communication continues for the duration ofthe communication session, i.e., call, data transfer, etc., until the communication session is terminated or a change in the operational profile of device 12 is detected (step S108).
  • the change in the operational profile of device 12 is detected in a fashion similar to the initial operational profile determined as described with respect to step SI 00 above.
  • base stations 14 can determine the degree of mobility of devices 12 and/or devices 12 can determine their own degree of mobility.
  • a nomadic device such as laptop 12d may have established communication based on its initial operational profile reflecting a stationary status. Laptop 12d may begin to move, thereby affecting a change in its operational status from stationary to mobile. Such is the case, for example, when laptop 12d is initially operated on a non- moving train or car which subsequently begins moving.
  • a potentially new carrier is selected based on the change (step SI 10).
  • the new carrier is preferably a carrier within the multi-carrier wideband communication environment.
  • a change in the operational profile of a device does not necessarily result in the selection of a new carrier. Such is the case, for example, where there are no available spreading codes in the reverse SCDMA link supported by the new carrier.
  • base station 14 preferably selects the new carrier, it is contemplated that the device 12 can select the new carrier and provide the new carrier information to the base station 14
  • step SI 12 a communication link is established using the new carrier. Techniques for switching between wireless carrier frequencies without terminating a communication session are known. Monitoring for a change in operational profile for subsequent new carrier selection in steps S108-S112 continues until the communication session is complete (step SI 14).
  • step SI 16 The operational profile is evaluated to determine whether the device is stationary or moving at a velocity faster than a predetermined amount. If a device is stationary (step SI 16) and spreading codes are available on one or more carriers supporting SCDMA (step SI 18), for example orthogonal Walsh spreading codes, a carrier having an SCDMA channel is selected (step SI 20). Such is the case with stationary wireless devices such as wireless tower computer 12b. If no spreading codes are available, a carrier having an ACDMA channel is used (step SI 22).
  • a carrier having an SCDMA channel is selected for a device which is generally not stationary (step SI 16) but which is not currently mobile (step S124) as long as spreading codes are available (step SI 18).
  • a carrier having an ACDMA channel is selected if spreading codes are not available.
  • step SI 24 Devices which are categorized as currently mobile (step SI 24), i.e., not stationary or having a degree of mobility more than the predetermined amount, such as wireless telephone 12a and vehicular mounted wireless device 12c, use carriers having an ACDMA channel (step SI 22).
  • the operational profile preferably indicates whether the device is stationary or mobile. It is contemplated, however, that the operational profile can indicate that a device is a nomadic device by storing a mobility history of the device. This mobility history is used to predict an initial operational characteristic ofthe device as stationary or mobile. As discussed above, devices which are typically stationary in use but which are suitable for mobile use are typically thought of as nomadic devices.
  • a device 12 using an SCDMA code can maintain soft handoff with base stations other than its primary base station 14, however, these other base stations 14 receive the SCDMA code as an ordinary pseudo-noise code generated by the combination ofthe orthogonal code and the "cover" scrambling code specific to each base station.
  • device 12 associated with a base station 14 (referred to herein as base station A) as the primary link has code CI from the SCDMA OVSF(orthogonal variable spreading factor) tree or orthogonal code set, and a scrambling code SI associated with base station A.
  • the transmission from device 12 to base station A uses an SCDMA mode while the same transmission received at base station B is experienced as just another pseudo-noise code.
  • a device 12 in SCDMA mode can maintain soft handoff with other base stations but cannot be operating in an SCDMA mode with those base stations unless those base stations have the same scrambling code (this arrangement might be applicable for a sectored cell site).
  • SCDMA mode devices in soft handoff will appear as interference to the SCDMA devices whose primary base station is base station B, since they are operating on the same carrier frequency.
  • Devices 12 in soft handoff can first be migrated to an ACDMA carrier because these devices' codes will be seen as pseudo-noise codes by the non-primary base stations and may thus become a source of interference to the in-cell (non-soft-handoff) SCDMA code users in these base stations.
  • the present invention advantageously provides a multi-carrier environment in which communication links, especially the reverse link, are established and maintained such that the link type selected is the optimal link for the device based on the operational profile ofthe device. Further, the type of communication link is changed when the operational profile changes in a manner which necessitates a change in link type, for example, a nomadic device using an SCDMA link begins moving such that ACDMA operation becomes preferable. As another example, the link may be changed when a device using an SCDMA code is in need of entering soft handoff.
  • the present invention provides a method for deriving the synchronization of device 12 when in soft handoff by measuring the received signal at secondary base stations 14.
  • the synchronization information is readily available to enable device 12 to instantaneously benefit from the use ofthe SCDMA code.
  • the present invention therefore advantageously provides a multi-carrier environment which supports both low and high mobility devices while accommodating devices whose mobility changes during use. Dividing the available bandwidth between a few subcarriers reduces the chip rate used per carrier. A lower chip rate makes it easier to establish and maintain the time alignment required for SCDMA operation. Devices which are able to effectively operate using an SCDMA carrier, i.e. low mobility devices, are isolated from the harmful effects of those devices which cannot maintain time alignment, such as high mobility devices. Recall that the strict time alignment requirements for SCDMA operation and the absence of synchronization within all secondary base stations in soft handoff reduce the benefit of SCDMA operation.
  • the individual carriers can be configured and re-configured to provide the optimal carrier type distribution suitable for the system environment.
  • a 5 MHz multi-carrier system supporting three 1.25 MHz carriers can be arranged such that the ratio of SCDMA carriers to ACDMA carriers is suited to the system and its users.
  • the provider ofthe system may allocate two carriers to SCDMA operation and one carrier to ACDMA operation. If the distribution of stationary to mobile devices changes, the provider can reconfigure the system to provide more ACDMA carriers and fewer SCDMA carriers or vice-versa as necessary.
  • the flexibility ofthe present invention allows the provider to optimize the carrier assignment ratio on a system-wide basis or on a per cell/section basis depending on the needs ofthe provider and the demand placed on the system.
  • the present invention addresses the complementary use of SCDMA codes and conventional pseudo-noise ACDMA codes on the reverse link of wireless communications systems.
  • SCDMA codes differ from ACDMA codes in that SCDMA codes are orthogonal codes which are tolerant only of minor deviations in chip timing alignment, and therefore require reasonably accurate chip synchronization.
  • SCDMA codes When applied to the reverse link for devices distributed over the area of a cell/sector, SCDMA codes enable the minimization of intra-cell interference and therefore result in increased capacity.
  • the present invention provides two access modes for use on the reverse link in which the mode best suited to the operational profile ofthe device is selected, thereby maximizing the benefits accruing from both the ACDMA and SCDMA access modes. The result is an increase in cell and system capacity.
  • frequency domain multiplexing FDM is employed to create separate communication channels for ADCMA communication and SCDMA communication. Because this arrangement employs smaller bandwidth carriers for each channel as opposed to a large single channel, the smaller bandwidth reduces the multipath resolution ofthe RAKE receiver in the base station.
  • FIG. 7 is similar to the arrangement shown in FIG. 1 with the addition of radio resource manager 44 (hereinafter referred to "RRM").
  • RRM 44 is shown coupled to base station 14.
  • RRM 44 can be included within the physical confines of base station 14 or can be coupled to the other elements of base station 14 via a remote network connection.
  • the physical location and placement of RRM 44 is not significant as long as the functionality provided by RRM 44 is available to a corresponding base station 14.
  • FIG. 7 shows one RRM 44 for each base station 14, it is further contemplated that a one-to-one relationship between base stations and RRMs is not required.
  • RRM 44 can be arranged to support one or more base stations 14.
  • RRM 44 is a general purpose or specialized computer arranged to execute programmatic software code to perform the below-described functions.
  • the computational performance and memory storage capacities of RRM 44 can be suitably sized by one of ordinary skill in the art to support the expected quantity of devices 12 and base stations 14.
  • RRM 44 preferably includes one or more of a volatile storage device such as a random access memory, non-volatile storage device such as a read only memory and/or fixed disc for programmatic software code storage, a central processing unit to execute the programmatic software code, and an interface to couple the RRM 44 to one or more ofthe other components of base station 14.
  • RRM 44 arranged in accordance with the present invention includes a number of additional aspects, namely the ability to manage code reuse and the ability to manage communication channel time slots based on orthogonality and/or soft handoff operation. Each of these additional functions are described in detail below.
  • code reuse and time slot management functions are described as additional functions performed by base station 44, it is contemplated that one or more of these additional functions can be implemented as part of a separate RRM 44.
  • more than one RRM 44 can be used to support a base station 14 such that existing RRM functions can be maintained on an existing RRM 44 with the additional functions described as part ofthe present invention implemented by another, new RRM 44 which supports the same base station 14.
  • programmatic software code upgrades and equipment retrofits can be avoided.
  • the described functions can be implemented as part of a new programmatic software code release and loaded into existing RRMs 44.
  • the total spread spectrum code used in a CDMA system includes a scrambling code and a spreading code.
  • the scrambling code is a portion ofthe total code common to a particular base station and is also used to identify the spreading code set(s) in use. This portion ofthe total code is managed and assigned by RRM 44 to each device 12 communicating with the corresponding base station 14.
  • the spreading code is the portion ofthe total code assigned to a particular wireless device 12 by RRM 44 and is used to identify communications received from wireless device 12. It is the spreading code portion ofthe total code which is assigned as orthogonal codes to wireless device 12 communicating in a SCDMA mode, and it is these orthogonal spreading codes which are limited as discussed above.
  • FIG. 8 shows an example of cell 46 corresponding to a base station 14 in FIG. 7.
  • Cell 46 supports two scrambling codes identified as SI and S2, and two spreading code sets identified as CI and C2.
  • the arrangement ofthe two scrambling codes and two orthogonal spreading codes yields four separate total codes.
  • the present invention is not limited to two scrambling codes and two spreading code sets per cell. Any quantity of each can be used depending on the capacity requirements of the cell.
  • total code 48 includes scrambling code S2 and orthogonal spreading code set CI; total code 50 includes scrambling code S2 and orthogonal spreading code set C2; total code 52 includes scrambling code S 1 and orthogonal spreading code set C2; and total code 54 includes scrambling code SI and orthogonal spreading code set CI.
  • Total codes which use the same scrambling code are orthogonal to one another but not to other scrambling codes within cell 46. As such, the total codes shown within rectangles in FIG. 8 are orthogonal to one another (total codes 48 and 50) as are the total codes shown within ovals (total codes 52 and 54). However, total codes 48 and 50 are not orthogonal to total codes 52 and 54. The result is quasi-orthogonality among the total codes within cell 46.
  • Quasi-orthogonality allows the same orthogonal spreading code set to be reused within a cell to increase the capacity within the cell to support additional devices 12 operating in an SCDMA mode.
  • RRM 44 further manages the communication channel by providing instruction to each wireless device 12 as to how many transmission frames device 12 may use to transmit or the duration of time device 12 may transmit using the assigned total code.
  • the wireless device capacity of each cell 46 is vastly increased over known CDMA systems.
  • FIG. 9 shows communication channel 56 divided into a plurality of time slots, namely time slots X, Y, through time slot Z. Methods for dividing a CDMA communication channel into time slots are known.
  • RRM 44 assigns time slots for uplink communication from wireless device 12 to base station 14 within cell 46. Each time slot supports communication from one or more wireless devices 12.
  • time slot table shown in FIG. 10 includes two time slots, namely time slot Y and time slot Y. Only two time slots are described for the sake of simplicity, it being understood that a similar table can be constructed which includes all time slots for a given channel managed by RRM 44.
  • time slot X supports devices A, C, E, and G.
  • Time slot Y supports wireless devices B, D, F, and H.
  • the wireless devices assigned to each communication time slot are preferably communicating in a mode which is orthogonal to each other device 12 assigned to the same time slot.
  • devices 12 assigned a total code from total code 48 or total code 50 as shown in FIG. 8 can each be assigned to one of time slot X or time slot Y.
  • devices 12 which were previously assigned the same time slot based on their ability to operate orthogonally may not currently be operating orthogonally.
  • those devices which are determined by RRM 44 not to be operating orthogonally are shown in FIG. 10 by a darkened orthogonality indicator 58.
  • devices C and G in time slot X and the devices B and F in time slot Y are not operating orthogonally.
  • the result is a degradation in the channel gain and a resultant reduction in the capacity ofthe channel.
  • RRM 44 reassigns time slots to optimize channel capacity by grouping devices 12 which can benefit from the use of orthogonal codes together.
  • An example of this regrouping is shown and described with reference to FIG. 11.
  • Channel conditions may be monitored, for example, by determining the received signal strength of previously scheduled transmissions or from signaling channels which may be used to maintain an ongoing low data rate signaling connection between a device and a base station.
  • time slot X has been reassigned by RRM 44 to devices which can benefit from orthogonal communication such as devices which are not in soft handoff.
  • devices A, D, E, and H are such devices. These devices are assigned spreading and orthogonal codes from total codes which are orthogonal to one another such as those shown in FIG. 8 as total codes 48 and 50, or total codes 52 and 54.
  • Devices which can not benefit from the use ofthe limited orthogonal codes are grouped together in another time slot such as time slot Y shown in FIG. 11 as including wireless devices B, C, F, and G.
  • Wireless devices B, C, F, and G may be devices which are in soft handoff with one or more other base stations.
  • a device in soft handoff can be synchronized, i.e. time- aligned to only one base station, devices in soft handoff may not be time-aligned with the other devices supported within cell 46.
  • the lack of gain observed in time slot Y is offset by the gain provided by grouping the orthogonal devices in time slot X.
  • FIG. 12 shows a sample performance evaluation for an exemplary test case where the maximum number of users per cell (capacity) is plotted as a function ofthe percentage of synchronized (SCDMA) users.
  • SCDMA percentage of synchronized
  • cell capacity is 37 users, and this can be increased to 44 users (a capacity increase of 19% over the partial orthogonality case) by reorganizing the time slot assignment to ensure that all ofthe synchronized SCDMA users are grouped together into the same time slot. It should be noted that test results are only for an exemplary test case, and capacity gains for other scenarios may be greater or less than the numbers given here.
  • the present invention advantageously provides RRM functions which, based in part on factors such as channel conditions and soft handoff requirements, expand the number of orthogonal codes available within cell 46. This is accomplished by reusing the codes to achieve a quasi-orthogonal environment and by assigning time slots in a manner which groups SCDMA communicating devices within one or more time slots to increase capacity within those time slots (a 10 dB gain within a time slot equates to approximately an 8x capacity increase) as compared with time slots which are not assigned based on the ability to benefit from orthogonal (SCDMA) codes.
  • RRM functions which, based in part on factors such as channel conditions and soft handoff requirements, expand the number of orthogonal codes available within cell 46. This is accomplished by reusing the codes to achieve a quasi-orthogonal environment and by assigning time slots in a manner which groups SCDMA communicating devices within one or more time slots to increase capacity within those time slots (a 10 dB gain within a time slot equates to approximately an 8x capacity increase) as compared
  • the present invention provides these advantages without adding complexity to system design because packet based systems typically have a RRM 44 to assign resources to the wireless devices.
  • the present invention advantageously provides an arrangement under which existing RRMs 44 take into consideration the performance characteristics of device 12 such as the operational profile described above, adverse channel conditions, i.e. multipath fading, and soft handover operation when determining the assignment of SCDMA or ACDMA codes, and the assignment of transmission time slots and transmission duration based on the assigned codes.
  • the present invention also advantageously provides a method which allows the use of a single large bandwidth carrier to support ACDMA and SCDMA codes, thereby avoiding the need to support multiple carriers with guard bands there between.

Abstract

L'invention concerne un système et un procédé de communication à accès multiple par répartition de code sans fil, comportant un procédé et un appareil d'attribution de porteuse d'accès multiple par répartition de code à créneaux temporels pour une communication de liaison inverse entre un dispositif et une station de base. Au moins une caractéristique de performances correspondant au dispositif est déterminée. Un code d'étalement d'accès multiple par répartition de code est attribué en fonction de cette/ces caractéristique(s) de performances déterminée(s). Un créneau temporel pour la communication avec la station de base est attribué en fonction de ce code d'étalement attribué. Selon un aspect, le code d'étalement attribué correspond soit à un code SCDMA, soit à un code ACDMA, de sorte qu'un créneau temporel correspondant à un code SCDMA représente un créneau temporel dans lequel tous les dispositifs sont de préférence en communication orthogonale alignée dans le temps avec la station de base. Il en résulte une augmentation dans le gain de canal et une augmentation dans la capacité de canal, par rapport à un système dans lequel des créneaux temporels soutiennent des codes SCDMA et ACDMA mélangés.
EP02712200A 2001-03-01 2002-02-28 Systeme et procede de communication a acces multiple par repartition de code sans fil Withdrawn EP1374423A2 (fr)

Applications Claiming Priority (5)

Application Number Priority Date Filing Date Title
US13562 1987-02-11
US797273 2001-03-01
US09/797,273 US6930470B2 (en) 2001-03-01 2001-03-01 System and method for code division multiple access communication in a wireless communication environment
US10/013,562 US7061898B2 (en) 2001-03-01 2001-12-11 System and method for time slotted code division multiple access communication in a wireless communication environment
PCT/IB2002/000605 WO2002071652A2 (fr) 2001-03-01 2002-02-28 Systeme et procede de communication a acces multiple par repartition de code sans fil

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CN1285238C (zh) 2006-11-15

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