WO2011145060A1

WO2011145060A1 - Apparatus and method for controlling a subchannel power imbalance ratio in communication systems

Info

Publication number: WO2011145060A1
Application number: PCT/IB2011/052169
Authority: WO
Inventors: Lars Christensen; Morten With Pedersen; Carsten Juncker
Original assignee: Nokia Corporation
Priority date: 2010-05-17
Filing date: 2011-05-17
Publication date: 2011-11-24

Abstract

An apparatus, method and system for controlling a subchannel power imbalance ratio in a communication system. In one embodiment, the apparatus includes a processor (420) and memory (450) including computer program code. The memory (450) and the computer program code configured to, with the processor (420), cause the apparatus to pair first and second mobile stations on first and second subchannels in a time slot, respectively, and vary a subchannel power imbalance ratio between the first and second subchannels for the first and second mobile stations, respectively.

Description

APPARATUS AND METHOD FOR CONTROLLING A SUBCHANNEL POWER IMBALANCE

RATIO IN COMMUNICATION SYSTEMS

TECHNICAL FIELD

The present invention is directed, in general, to communication systems and, in particular, to an apparatus, method and system for controlling a subchannel power imbalance ratio in a communication system.

BACKGROUND

The Third Generation Partnership Project ("3GPP") is an international association of telecommunications network operators and manufacturers hosted by the International

Telecommunications Union ("ITU") to develop and evolve standards for mobile communications systems. The standards developed by the 3GPP have evolved from standards developed for the Global System for Mobile Communications ("GSM"). A GSM network or communication system is primarily a mobile communication system employing digital techniques for signaling, speech and data. The wide international deployment of GSM has enabled subs cribers to use their mobile stations in many parts of the world.

A GSM network or communication system employs a variant of phase-shift keying ("PSK") with time division multiple access ("TDMA") signaling over frequency division duplex ("FDD") carriers. The GSM standards have evolved to include short message service ("SMS," also referred to as text messaging), packet data capabilities, and higher speed data transmission using Enhanced Data Rates for GSM Evolution ("EDGE").

The GSM network or communication system in 3GPP includes network communication elements providing user plane (including packet data convergence protocol/radio link control/medium access control/physical sublayers) and control plane protocol terminations towards wireless communication devices such as cellular telephones. A network communication element such as a base station ("BS") is an access entity of a communication network, and the term will generally refer to equipment providing the wireless-network interface in a cellular telephone system, including cellular telephone systems other than those designed under 3GPP standards. A wireless communication device or terminal is generally known as a mobile station ("MS"), user equipment ("UE") or cellular telephone.

As wireless communication systems such as cellular telephone, satellite, and microwave communication systems become widely deployed and continue to attract a growing number of users, there is a pressing need to accommodate a large and variable number of communication devices transmitting a growing range of communication applications with fixed communication resources, and a growing need to conserve energy in base stations and wireless communication devices. A current topic in 3GPP of general interest is the saving of energy in the wireless (e.g., cellular) communication system or network. An example of a feature to increase speech capacity and reduce energy consumption in a wireless communication system such as in a GSM network is the use of an orthogonal subchannel ("OSC") that is used in voice services over adaptive multi-user channels on one slot ("VAMOS"). The OSC principle used in VAMOS allows two full-rate Gaussian minimum shift key ("GMSK") mobile stations or four half-rate GMSK mobile stations to be multiplexed onto a single timeslot by transmitting two GMSK signals as one quadrature phase shift keyed ("QPSK") signal from a base station. Using OSC for

VAMOS, the speech capacity of a GSM network may be more or less doubled compared to existing GSM networks using GMSK for speech information.

A present concern with the use of an orthogonal subchannel is the introduction of co-channel interference between the two subchannels that share a common timeslot in a signal transmitted from a base station. For example, some commercially available downlink advanced receiver performance

("DARP") phase I mobile stations can be very sensitive to subchannel power imbalance ratio ("SCPIR"). Such mobile stations can drop a call within a few minutes when such mobile stations (or the respective subchannels) are allocated a low subchannel power imbalance ratio. Another concern is that many existing mobile stations have not been specified nor tested for operation using orthogonal subchannel. Accordingly, unreliable operation for such mobile stations should be expected under such conditions In view of the growing deployment of communication systems such as cellular communication systems, it would be beneficial to be able to use VAMOS with legacy mobile stations such as existing DARP phase I mobile stations that are already in GSM networks or communication systems without introducing unreliable operation for such mobile stations, while taking advantage of VAMOS compliant mobile stations. The result would be increased network capacity as well as increased energy efficiency for such communication systems.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, and technical advantages are generally achieved, by embodiments of the present invention, which include an apparatus, method and system for controlling a subchannel power imbalance ratio in a communication system. In one embodiment, the apparatus includes a processor and memory including computer program code. The memory and the computer program code configured to, with the processor, cause the apparatus to pair first and second mobile stations on first and second subchannels in a time slot, respectively, and vary a subchannel power imbalance ratio between the first and second subchannels for the first and second mobile stations, respectively.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures or processes for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIGURES 1 to 3 illustrate system level diagrams of embodiments of communication systems that provide an environment for application of the principles of the present invention;

FIGURE 4 illustrates a system level diagram of an embodiment of a communication element of a communication system for application of the principles of the present invention;

FIGURE 5 illustrates a block diagram of an embodiment of portions of a base station of a communication system for application of the principles of the present invention; FIGURE 6 illustrates a graphical representation of an embodiment of bit mapping of information with respect to mobile stations in accordance with the principles of the present invention;

FIGURE 7 illustrates a graphical representation of an exemplary temporally varying subchannel power imbalance ratio for a mobile station in accordance with the principles of the present invention; and

FIGURE S illustrates a flowchart of an exemplary method to vary a subchannel power imbalance ratio for mobile stations in accordance with the principles of the present invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention. In view of the foregoing, the present invention will be described with respect to exemplary embodiments in a specific context of an apparatus, method and system to control a subchannel power imbalance ratio between two paired subchannels to manage a level of interference between mobile stations employing two paired subchannels in a communication system. Although systems and methods described herein are described with reference to a GSM network, they can be applied to any

communication system including future GSM and 3GPP Long Term Evolution ("LTE") communication systems or networks (e.g., UMTS, LTE, and its future variants such as 4th generation ("4G") communication systems). Turning now to FIGURE 1 , illustrated is a system level diagram of an embodiment of a communication system including a base station 115 and wireless communication devices (e.g., a mobile stations ("MS"), also generally referred to as a user equipment ("UE")) 135, 140, 145 that provides an environment for application of the principles of the present invention. The base station 115 is coupled to a public switched telephone network (not shown). The base station 115 (also referred to as a base station system, "BSS") is configured with a plurality of antennas to transmit and receive signals in a plurality of sectors including a first sector 120, a second sector 125, and a third sector 130, each of which typically spans 120 degrees. Although FIGURE 1 illustrates one wireless communication device (e.g., wireless communication device 140) in each sector (e.g., the first sector 120), a sector may generally contain a plurality of wireless communication devices. In an alternative embodiment, the base station 115 may be formed with only one sector and multiple base stations may be constructed to transmit according to collaborative/cooperative multiple-input multiple-output ("C-MIMO") operation, etc. The plurality of sectors 120, 125, 130 are formed by focusing and phasing radiated signals from the base station antennas, and separate antennas may be employed per sector. The plurality of sectors 120, 125, 130 increases the number of subscriber stations (e.g., the wireless communication devices 135, 140, 145) that can simultaneously communicate with the base station 115 without the need to increase the utilized bandwidth by reduction of interference that results from focusing and phasing base station antennas.

Turning now to FIGURE 2, illustrated is a system level diagram of an embodiment of a communication system including wireless communication devices (e.g., a mobile station ("MS")) 260, 270 that provides an environment for application of the principles of the present invention. The communication system includes base stations 210, 211 coupled by communication paths or links 220, 221 (e.g., by a fiber-optic communication path) to a core telecommunications network such as public switched telephone network ("PSTN") 230 through a base station controller ("BSC") 231 and a mobile switching center ("MSC") 232. The base station controller 231 provides a level of control behind a group of base stations 210, 211 . The base station controller 231 handles the allocation of radio channels, receives measurements from the mobile stations 260, 270, controls handovers from base station to base station. The mobile switching center 232 is the primary service delivery node for communications (e.g., GSM service) that handles voice calls and short message service as well as other services such as conference calls, facsimile and circuit switched data. The mobile switching center 232 sets up and releases the end- to-end connection, handles mobility and hand-over requirements during the call and takes care of charging and real-time pre-paid account monitoring. The base station 210 is coupled by wireless communication paths or links 240, 250 to the mobile stations 260, 270, respectively, that lie within its cellular area 290. The mobile switching center 232 may be coupled to a visitor location register ("VLR") 233 that in turn is coupled to a home location register ("HLR") 234. The visitor location register 233 provides a listing of the mobile stations 260, 270 that have roamed into the particular area served by one or more base stations 210. The home location register 234 is a central network database that contains details of each mobile station that is authorized to use the GSM network. A subscriber identity module ("SIM") (a removable card in a mobile station 260, 270) stores the subscriber' s key that identifies the subscriber, phone number, network authorization data, personal security keys, contact lists, and stored text messages on a mobile station such as a personal computer to the home location register. Security features for the subscriber identity module include authentication and encryption measures to protect data therein and to prevent eavesdropping. The subscriber identity module allows a subscriber to change mobile stations 260, 270 by simply transferring the subscriber identity module into another mobile station 260, 270.

In operation of the communication system illustrated in FIGURE 2, the base station 210 communicates over an air interface with each mobile station 260, 270 through control and data communication resources allocated by the base station 210 over the communication paths 240, 250, respectively. A standard for the air interface can conform to any suitable standard or protocol, and may enable voice and data traffic such as data traffic enabling Internet access. The air interface may include, without limitation, time division multiple access ("TDMA") that supports a GSM or related protocol. The communication system illustrated in FIGURE 2 may include further network elements such as a Serving General Packet Radio Service ("GPRS") Support Node ("SGSN") (not shown). It is recognized that local area networks such as WiFi networks can provide an alternative means of communication access for a mobile station compared to Global System for Mobile Communications ("GSM"), the Universal Mobile Telecommunications System ("UMTS"), High Speed Packet Access ("HSPA") and LTE communication systems or networks. Unlike a wide area network, a local area network such as WiFi can utilize portions of the license- exempt spectrum to take advantage of additional bandwidth to provide high-speed communications access. Since a mobile station will likely be able to operate with a transceiver that can access the local area network and the wide area network, the wide area network can be utilized to enhance the mobile station experience in the local area network. Applications (e.g., middleware) running on the mobile station can decide whether use an available local area network, the wide area network, or both at the same time for Internet services. The local area network can be structured so that selected services such as voice or emergency calls will still be available to the mobile station through the wide area network. Hence, the mobile station will not completely hand over its communications operations to the local area network, but dual radio operation is preferable when accessing the local area network. Thus, a level of cooperation between the wide area network and the local area network during local area network access is preferable. As used herein, a wide area network (or system or communication system) refers to a network that provides communication services employing a plurality of base stations with access to a common backbone such as a PSTN. A wide area network provides communication services over a broad physical area including communication paths or links that cross metropolitan, regional or national boundaries. The operation of the plurality of base stations is coordinated across the wide area network so that the mobile station can move seamlessly with handovers across the broad physical area served by the wide area network. Examples of wide area networks include networks operated by commercial communication system operators such as Verizon and AT&T for the benefit of customers, with telecommunications services provided under established tariffs. The wide area networks may be structured with systems designed according to 3GPP specifications, including various levels of advanced capability, or with other standards such as compatible with 3GPP LTE or Worldwide Interoperability for Microwave Access ("WiMAX") communication systems.

A local area network (or system or communication system) refers to a network that provides isolated nodes of communication service by an enterprise such as a home, office, hotel, campus, airport, and for enterprise members such as family members, students or employees. The services provided at one node of a local area network are generally not coordinated with services provided by another node. A local area network is typically managed by the enterprise or a surrogate thereof. For example, a person may turn off a router that provides services in his home, or change the channels over which the local area network operates. The operation of a router in one home will generally be uncoordinated with the operation of a router in a neighbor's home, and access to one will not be coordinated with access to the other. A local area network may be coupled to a PSTN through a port such as a fiber port, a coaxial line, one or more tip-and-ring pairs, or a microwave link that communicates with the PSTN through a wide area network. An example of a local area network is a wireless network in a home or business environment operating under the IEEE standards 802.11 , which is incorporated herein by reference, that describe WiFi communication.

The 3GPP is a likely forum for standardization of a wide area network such as the LTE cellular network operation with a wireless local area ("LA") network or system. A GSM network would be positioned as a 3GPP system, challenging current wireless local area network ("WLAN") systems structured with earlier designs. To achieve standardization in 3GPP, acceptance from communication system operators is needed. An area of interest for communication system operators is that they can offload bulk Internet traffic from the wide area network to a local area network, while offering a seamless mobile station experience for their services in the local area network. To enable such offloading of services, it is reasonable to assume that local area network operation is supported by the wide area network with cooperation therebetween.

Design details of the GSM/EDGE are generally provided in the 3GPP Technical Specification ("TS") 45 series issued by the 3GPP. For example, the physical layer specification produced by the GSM/EDGE Technical Specification Group is described in 3 GPP TS 45.001 entitled "Radio Access Network; Physical Layer on the Radio Path; General Description," Release 9, dated May 2009, and the modulation specification is provided in 3GPP TS 45.004 entitled "Radio Access Network; Modulation," Release 8, dated December 2008. The overall network architecture is described in 3GPP TS 23.002 entitled "Network Architecture," Release 9, dated June 2009, and an extensive list of technical specifications for GSM systems is given in 3GPP TS 41. 101 , entitled "Technical Specifications and

Technical Reports for a GERAN-Based 3 GPP System," Release 8, dated June 2009. The aforementioned specifications and others provided herein are incorporated herein by reference.

Turning now to FIGURE 3, illustrated is a system level diagram of an embodiment of a communication system that provides an environment for application of the principles of the present invention. The communication system includes a wide area network (e.g., a wireless communication system such as a GSM network) formed with a plurality of base stations 310, 320, 330 that provide support for the operation thereof and the operation of the local area network. The mobile stations (one of which is designated 350) can communicate with both the wide area network and the local area network. The local area network is formed with a wireless router 340 that provides local wireless communications services, and may provide access to a local computer and perhaps other devices such as a wireless printer. The local area network provides the mobile station 350 with user plane ("U-plane") data and at least a portion of control plane ("C-plane") messages that are supported through the wide area network. As introduced herein, the local area access point such as the router 340 illustrated in FIGURE 3 may communicate with a local area support node (or support node) that may be located in a server of the wide area network or in an Internet-related facility. Turning now to FIGURE 4, illustrated is a system level diagram of an embodiment of a communication element 410 of a communication system for application of the principles of the present invention. The communication element or device 410 may represent, without limitation, a base station, a wireless communication device (e.g., a subscriber station, terminal, mobile station, user equipment, machine), a network control element, a communication node, or the like. The communication element 410 includes, at least, a processor 420, memory 450 that stores programs and data of a temporary or more permanent nature, an antenna(s) 460, and a radio frequency transceiver 470 coupled to the antenna 460 and the processor 420 for bidirectional wireless communication. The communication element 410 may provide point-to-point and/or point-to-multipoint communication services. The communication element 410, such as a base station in a cellular network, may be coupled to a communication network element, such as a network control element 480 of a public switched telecommunication network ("PSTN"). The network control element 480 may, in turn, be formed with a processor, memory, and other electronic elements (not shown). The network control element 480 generally provides access to a telecommunication network such as a PSTN. Access may be provided using fiber optic, coaxial, twisted pair, microwave communication, or similar link coupled to an appropriate link-terminating element. A communication element 410 formed as a wireless

communication device is generally a self-contained device intended to be carried by an end user or subscriber.

The processor 420 in the communication element 410, which may be implemented with one or a plurality of processing devices, performs functions associated with its operation including, without limitation, encoding and decoding (encoder/decoder 423) of individual bits forming a communication message, formatting of information, and overall control (controller 425) of the communication element, including processes related to management of communication resources (resource manager 428).

Exemplary functions related to management of communication resources include, without limitation, hardware installation, traffic management, performance data analysis, tracking of end users and equipment, configuration management, end user administration, management of wireless communication devices, management of tariffs, subscriptions, security, billing and the like. For instance, in accordance with the memory 450, the resource manager 428 is configured to allocate primary and second communication resources (e.g., time and frequency communication resources) for transmission of voice communications and data to/from the communication element 410 and to format messages including the communication resources therefor in a primary and secondary communication system.

The execution of all or portions of particular functions or processes related to management of communication resources may be performed in equipment separate from and/or coupled to the communication element 410, with the results of such functions or processes communicated for execution to the communication element 410. The processor 420 of the communication element 410 may be of any type suitable to the local application environment, and may include one or more of general -purpose computers, special purpose computers, microprocessors, digital signal processors ("DSPs"), field- programmable gate arrays ("FPGAs"), application-specific integrated circuits ("ASICs"), and processors based on a multi-core processor architecture, as non-limiting examples.

The transceiver 470 of the communication element 410 modulates information on to a carrier waveform for transmission by the communication element 410 via the antenna 460 to another communication element. The transceiver 470 demodulates information received via the antenna 460 for further processing by other communication elements. The transceiver 470 is capable of supporting duplex operation for the communication element 410.

The memory 450 of the communication element 410, as introduced above, may be one or more memories and of any type suitable to the local application environment, and may be implemented using any suitable volatile or nonvolatile data storage technology such as a semiconductor-based memory device, a magnetic memory device and system, an optical memory device and system, fixed memory, and removable memory. The programs stored in the memory 450 may include program instructions or computer program code that, when executed by an associated processor, enable the communication element 410 to perform tasks as described herein. Of course, the memory 450 may form a data buffer for data transmitted to and from the communication element 410. Exemplary embodiments of the system, subsystems, and modules as described herein may be implemented, at least in part, by computer software executable by processors of, for instance, the wireless communication device and the base station, or by hardware, or by combinations thereof. As will become more apparent, systems, subsystems and modules may be embodied in the communication element 410 as illustrated and described herein. Modulation of an orthogonal subchannel ("OSC") allows two traditional Gaussian minimum shift key speech signals (each of which is called a subchannel in the following) to be served by the same timeslot for transmission by using alpha-QPSK modulation carrying twice the number of bits per symbol. GMSK refers to shaping the waveform of digital data with a Gaussian filter before modulation to reduce sideband energy. However, this multiplexing of two subchannels onto a single timeslot may introduce co-channel interference between the two subchannels that share the same timeslot in the signal transmitted from a base station.

A feature called voice services over adaptive multi-user channels on one slot ("VAMOS") is currently being specified for 3GPP Release 9, which introduces a formal framework for OSC including new training sequence sets, adaptive power allocation between paired subchannels, and certification tests that confirm VAMOS compliant mobile stations can operate reliably under such interference. However, communication system or network operators are naturally interested in using the OSC and VAMOS concepts with existing mobile stations in the network. Existing DARP phase I compliant mobile stations may allow the use of such concepts with help of the presented solution. A significant problem with using DARP phase I mobile stations for OSC and VAMOS is that such mobile stations were not specified for, nor tested in, such scenarios, and unreliable operation may occur under such conditions. Specifically, synchronization functions (e.g., automatic frequency control) of a mobile station may not operate as desired when subjected to the special form of interference that occurs in an OSC or VAMOS

communication mode. Processes introduced herein can alleviate such undesired behavior.

Turning now to FIGURE 5, illustrated is a block diagram of an embodiment of portions of a base station of a communication system for application of the principles of the present invention. A first mobile station produces information (e.g. , voice, video or data) as part of a communication that are received in a first queue 501 and a second mobile station produces information (e.g. , voice, video or data) as part of a communication that are received in a second queue 51 1 . The information from the first and second mobile stations is then encoded via a first and second channel coder 502, 512, respectively, and the encoded information is formatted via first and second burst builders 503, 513, respectively. For the purposes of this example, the first mobile station is a legacy mobile station (e.g., a non-VAMOS compliant mobile station) and the second mobile station is a VAMOS compliant mobile station. Thus, each of the subchannels (e.g., first and second subchannels in a time slot) is assigned a training sequence from a specific set of training sequences. The first burst builder 503 is assigned a training sequence code ("TSC") for use with the first mobile station (and the first subchannel) and the second burst builder 513 is assigned new orthogonal training sequence code for the second mobile station (and the second subchannel). Other combinations of training sequence codes can also be used if desired (e.g. , two training sequence codes from a set of legacy training sequence codes).

In VAMOS, each of the multiuser channels is assembled as a combination of a pair of traffic channels mapped onto the same communication resource using alpha-QPSK modulation via a modulator 504. In a rotator 505, the complex constellation symbols representing the information to be transmitted are rotated π/2 radians. In a pulse shaper 506, the signal to be transmitted is modulated employing linearized Gaussian minimum shift keying ("LGMSK") and thereafter transmitted via antenna(s) 507. The portions of the base station as described herein may be embodied in a processor and/ or transceiver in cooperation with memory as illustrated and described with respect to FIGURE 4. When communication systems or networks operate in VAMOS communication mode, the SCPIR value is used to control how transmission power (i. e. , transmit power level) is split between two paired subchannels. The value of the SCPIR is set to:

SCPIR = P 1/P2, wherein PI and P2 are the transmission powers of VAMOS subchannel 1 and subchannel 2, respectively. As a result, adjusting the SCPIR value allows a base station to control the allocation of power between two paired subchannels. When the value of SCPIR is equal to one, the two subchannels are allocated the same power and, thus, the power of the interfering subchannel will have the same power as the desired subchannel regardless of the subchannel a given mobile station detects. However, it may be desirable to have a value of SCPIR different from one in order to allocate more power to one of the two subchannels (i.e., to allocate different power levels for the underlying paired mobile stations). Furthermore, an unequal value of SCPIR (i.e., unequal to one) results in one subchannel having more power than the other, it also changes the ratio of desired power to interfering power as seen from the point of view of each subchannel. In this case, the subchannel having the smaller power allocation will experience a significantly higher level of interference, and the undesired behavior resulting from this increased level of interference is resolved for legacy mobile stations by processes introduced herein. Turning now to FIGURE 6, illustrated is a graphical representation of an embodiment of bit mapping of information with respect to mobile stations in accordance with the principles of the present invention. The illustrated embodiment demonstrates two mobile stations with a QPSK modulation that is a subset of SPSK (i.e., a phase shift- keyed constellation with eight constellation elements) to illustrate unequal division of power between the two mobile stations. The horizontal "I" axis represents the in- phase component of each constellation element, and the vertical "Q" axis represents the quadrature component of each constellation element. The first mobile station is mapped to a first bit (i. e., on the horizontal axis) and the second mobile station is mapped to the second bit (i. e., on the vertical axis). Thus, the resulting signals for the first and second mobile stations appear along the I or Q axis, respectively. The result is unequal transmit power levels for the first and second mobile stations, wherein the first mobile station employs a higher transmit power level than the second mobile station.

Traditionally, only a single subchannel is transmitted per timeslot and, therefore, no (or insignificant) interference to a subchannel is present in the signal transmitted from a given base station. This is the assumption under which the legacy and DARP phase I mobile stations have been designed and specified, simplifying the tasks of continuous synchronization and detection performed in a receiving mobile station. The principle described herein to mitigate the impact of interference present in paired subchannels due to OSC or VAMOS is, therefore, not usually required in non-OSC based communication systems or networks because the interference problem does not typically exist. The same problem of OSC or VAMOS interference also exists for VAMOS compliant mobile stations, but these mobile stations have been designed and tested for such scenarios and are, therefore, capable of reliably handling the interference. A process for allowing continuous operating functions impaired by OSC or VAMOS interference

(referring here to co-channel interference originating from the paired subchannel) including

synchronization functions is introduced to effectively reduce OSC or VAMOS interference. This result is achieved by changing the SCPIR over time whenever a mobile station that is not VAMOS compliant is paired with a VAMOS compliant mobile station and is done in order to provide a sufficient number of bursts of symbols with reduced interference levels to the non-VAMOS compliant mobile station. When a burst with reduced interference level is received by the non-VAMOS compliant mobile station, this is exploited by the mobile station to perform functions otherwise impaired by the interference, such as a synchronization/automatic frequency control function. Naturally, the reduced level of interference should occur often enough for the mobile station to operate as desired (e.g., not lose synchronization to the communication system), but should not be done too often as the VAMOS compliant mobile station may otherwise drop its call.

The SCPIR is changed as a function of time to provide bursts with reduced levels of interference for the non-VAMOS complaint mobile station of two paired OSC or VAMOS subchannels. The temporal SCPIR variation used can be any pattern of SCPIR values that achieves the goal of providing bursts to the non-VAMOS complaint mobile station so that reception can be maintained (e.g., continuous

synchronization can be maintained despite an otherwise high level of interference).

Turning now to FIGURE 7, illustrated is a graphical representation of an exemplary temporally varying SCPIR for a mobile station (e.g., a legacy or non-VAMOS compliant mobile station) in accordance with the principles of the present invention. The horizontal axis represents time and the vertical axis represents the SCPIR value. The time-variation of SCPIR, without limitation, is periodic for a subchannel having a period of N = Na + Nb bursts. A value of SCPIR equal to p_a is used for a duration of Na bursts for the two paired subchannels, followed by a value of SCPIR equal to pi, for Nb bursts for the two paired subchannels. Thus, the transmit power levels are selected and, in this case, alternately increased and decreased to accommodate the Na and b bursts during the respective durations (or intervals) of the period (or time slot) N. In this particular example, the SCPIR pattern is periodic, which is a practical exemplary configuration of the SCPIR pattern for many applications. Exemplary values may be p_a = 4 decibels ("dB") for Na = 99 bursts followed by p_¾ = -10 dB for Nb=l burst. For these exemplary values, the weaker subchannel would experience a carrier-to-interference ratio ("OR") of -4 dB during the Na bursts, which would then be compensated by a CIR of 10 dB during the following Nb bursts. Variations such as using more than two SCPIR values fall within the scope of the present invention.

An advantage of a time-varying value of SCPIR is that it enables the use of OSC or VAMOS with legacy and DARP Phase I mobile stations that are already in GSM networks or communication systems, since the implementation of time-varying value of SCPIR can be performed in modules (e.g., software modules) of the base stations. For network operators, this means that the advantage of VAMOS compliant mobile stations can also be achieved with legacy and DARP Phase I mobile stations, thereby increasing communication system or network capacity, reducing energy consumption, and exploiting available spectrum more efficiently. The performance of the VAMOS compliant subchannel (and thereby the mobile station of that subchannel) may be slightly degraded to improve operation of the non- VAMOS compliant subchannel. Turning now to FIGURE S, illustrated is a flowchart of an exemplary method to vary a subchannel power imbalance ratio for mobile stations in accordance with the principles of the present invention. The method begins in a step or module 810 wherein mobile stations are paired on an orthogonal subchannels in a time slot. The method continues by selecting a SCPIR for the two subchannels (each carrying information from one of the paired mobile stations) in a step or module 820. The method continues by ascertaining if a SCPIR is approximately equal to one (e.g., it may check whether SCPIR is exactly equal to one or whether the power imbalance is less than, for example, one decibel) in a step or module S30. When the value of SCPIR is approximately equal to one, the two subchannels are allocated the same transmit power level as the method confirms the SCPIR value as one in a step or module 850 and the method thereafter ends in a step or module 870. While in this exemplary embodiment, the method ends in the step or module 870 when the SCPIR is approximately equal to one, it should be understood that the transmit power levels of the subchannels may be varied (via the step or module 850) even when the SCPIR is approximately equal to one. If the value of SCPIR is not approximately equal (unequal) to one, then the subchannels may be allocated different transmit power levels for the paired mobile stations.

The method continues with a decisional step or module 840 to determine if both mobile stations are VAMOS compliant mobile stations. If both paired mobile stations are VAMOS compliant, then the method sets the SCPIR value in the step or module 850 and then ends in step or module 870. If at least one mobile station is not a VAMOS compliant mobile station, then the method sets the SCPIR values and respective intervals in a step or module 860 and the method thereafter ends in a step or module 870. For instance, for a period N, the method may set the transmit power level of one subchannel to a higher level for a duration (or interval) of Na bursts and to a lower level for a duration of Nb bursts {e.g., select or alternately change the transmit power level for the intervals to accommodate the Na and Nb bursts during the period or time slot). Of course, the change in transmit power level for one of the paired mobile stations through changing the value of the SCPIR also changes the transmit power level of the other paired mobile station in order to keep the sum-power level constant. Should no such sum-power constraint be present, the transmit power level of the weaker subchannel may naturally be changed independent of the transmit power level of the stronger subchannel.

Thus, an apparatus, method and system are introduced herein for use in communication system. In one embodiment, an apparatus (e.g., a base station) includes a processor and memory including computer program code. The memory and the computer program code are configured to, with the processor, cause the apparatus to pair first and second mobile stations on first and second subchannels in a time slot, respectively, and select a transmit power level for one of the first and second subchannels for the first and second mobile stations, respectively. In accordance therewith, the apparatus is configured to alternately increase and decrease the transmit power level for one of the first and second subchannels for the first and second mobile stations, respectively. A subchannel power imbalance ratio between the first and second subchannels is a function of the transmit power level for the first and second subchannels. Additionally, a sum-power level for the transmit power levels for the first and second subchannels may remain constant. The apparatus is configured to set (or vary) the subchannel power imbalance ratio between the first and second subchannels. The apparatus is also configured to determine if the subchannel power imbalance ratio between the first and second subchannels is approximately equal to one. Additionally, the apparatus is configured to format information for the first and second mobile stations employing different training sequence codes for the first and second subchannels, respectively. The apparatus is also configured to determine if at least one of the first and second mobile stations is a non-VAMOS compliant mobile station, and set (or vary) the subchannel power imbalance ratio and respective interval for the first and second subchannels accordingly. Although the apparatus, method and system described herein have been described with respect to a GSM network or communication system, the apparatus, method and system are equally applicable to other types of communication systems such as an LTE or a WiMax^® communication system.

Program or code segments making up the various embodiments of the present invention may be stored in a computer readable medium or transmitted by a computer data signal embodied in a carrier wave, or a signal modulated by a carrier, over a transmission medium. For instance, a computer program product including a program code stored in a computer readable medium (e.g., a non- transitory computer readable medium) may form various embodiments of the present invention. The "computer readable medium" may include any medium that can store or transfer information. Examples of the computer readable medium include an electronic circuit, a semiconductor memory device, a read only memory ("ROM"), a flash memory, an erasable ROM ("EROM"), a floppy diskette, a compact disk ("CD")-ROM, an optical disk, a hard disk, a fiber optic medium, a radio frequency ("RF") link, and the like. The computer data signal may include any signal that can propagate over a transmission medium such as electronic communication network channels, optical fibers, air, electromagnetic links, RF links, and the like. The code segments may be downloaded via computer networks such as the Internet, Intranet, and the like. As described above, the exemplary embodiment provides both a method and corresponding apparatus consisting of various modules providing functionality for performing the steps of the method. The modules may be implemented as hardware (embodied in one or more chips including an integrated circuit such as an application specific integrated circuit), or may be implemented as software or firmware for execution by a computer processor. In particular, in the case of firmware or software, the exemplary embodiment can be provided as a computer program product including a computer readable storage structure embodying computer program code (i.e., software or firmware) thereon for execution by the computer processor.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. For example, many of the features and functions discussed above can be implemented in software, hardware, or firmware, or a combination thereof. Also, many of the features, functions and steps of operating the same may be reordered, omitted, added, etc., and still fall within the broad scope of the present invention.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.

Claims

WHAT IS CLAIMED IS:

1. An apparatus, comprising:

a processor; and

memory including computer program code,

said memory and said computer program code configured to, with said processor, cause said apparatus to perform at least the following:

pair first and second mobile stations on first and second subchannels in a time slot, respectively, and

vary a subchannel power imbalance ratio between said first and second subchannels for said first and second mobile stations, respectively.

2. The apparatus as recited in Claim 1 wherein said memory and said computer program code are further configured to, with said processor, cause said apparatus to ascertain if at least one of said first and second mobile stations is a non-voice services over adaptive multi-user channels on one slot (VAMOS)-compliant mobile station and vary said subchannel power imbalance ratio in dependence of said ascertaining.

3. The apparatus as recited in Claim 1 wherein said subchannel power imbalance ratio between said first and second subchannels is a function of transmit power levels for said first and second subchannels and a sum-power level for said transmit power levels remains constant.

4. The apparatus as recited in Claim 1 wherein said memory and said computer program code are further configured to, with said processor, cause said apparatus to select a transmit power level for at least one of said first and second subchannels for said first and second mobile stations, respectively, to vary said subchannel power imbalance ratio.

5. The apparatus as recited in Claim 1 wherein said memory and said computer program code are further configured to, with said processor, cause said apparatus to alternately increase and decrease a transmit power level for at least one of said first and second subchannels for said first and second mobile stations, respectively, to vary said subchannel power imbalance ratio.

6. The apparatus as recited in Claim 1 wherein said memory and said computer program code are further configured to, with said processor, cause said apparatus to determine if said subchannel power imbalance ratio between said first and second subchannels is approximately equal to one.

7. The apparatus as recited in Claim 1 wherein said memory and said computer program code are further configured to, with said processor, cause said apparatus to format information for said first and second mobile stations employing different training sequence codes for said first and second subchannels, respectively.

S. An apparatus, comprising:

means for pairing first and second mobile stations on first and second subchannels in a time slot, respectively, and

means for varying a subchannel power imbalance ratio between said first and second subchannels for said first and second mobile stations, respectively.

9. The apparatus as recited in Claim 8 further comprising means for ascertaining if at least one of said first and second mobile stations is a non- voice services over adaptive multi-user channels on one slot (VAMOS)-compliant mobile station; said means for varying operating in dependence of said ascertainng

10. The apparatus as recited in Claim S wherein said subchannel power imbalance ratio between said first and second subchannels is a function of transmit power levels for said first and second subchannels and a sum-power level for said transmit power levels remains constant.

11. A computer program product comprising program code stored in a computer readable medium configured to:

pair first and second mobile stations on first and second subchannels in a time slot, respectively, and vary a subchannel power imbalance ratio between said first and second subchannels for said first and second mobile stations, respectively.

12. The computer program product as recited in Claim 11 wherein said program code stored in said computer readable medium is further configured to ascertain if at least one of said first and second mobile stations is a non-voice services over adaptive multi-user channels on one slot (VAMOS)- compliant mobile station and to vary said subchannel power imbalance ratio in dependence of said ascertaining.

13. The computer program product as recited in Claim 11 wherein said subchannel power imbalance ratio between said first and second subchannels is a function of transmit power levels for said first and second subchannels and a sum-power level for said transmit power levels remains constant.

14. A method, comprising:

pairing first and second mobile stations on first and second subchannels in a time slot, respectively, and

varying a subchannel power imbalance ratio between said first and second subchannels for said first and second mobile stations, respectively.

15. The method as recited in Claim 14 further comprising ascertaining if at least one of said first and second mobile stations is a non-voice services over adaptive multi-user channels on one slot (VAMOS)-compliant mobile station and varying said subchannel power imbalance ratio in dependence of said ascertaining.

16. The method as recited in Claim 14 wherein said subchannel power imbalance ratio between said first and second subchannels is a function of transmit power levels for said first and second subchannels and a sum-power level for said transmit power levels remains constant.

17. The method as recited in Claim 14 further comprising selecting a transmit power level for at least one of said first and second subchannels for said first and second mobile stations, respectively, to vary said subchannel power imbalance ratio.

18. The method as recited in Claim 14, further comprising alternately increasing and decreasing a transmit power level for at least one of said first and second subchannels for said first and second mobile stations, respectively, to vary said subchannel power imbalance ratio.

19. The method as recited in Claim 14 further comprising determining if a subchannel power imbalance ratio between said first and second subchannels is approximately equal to one.

20. The method as recited in Claim 14 further comprising formatting information for said first and second mobile stations employing different training sequence codes for said first and second subchannels, respectively.