HK1075161A - An improved control - hold mode - Google Patents

Description

Improved control-hold mode

Background

FIELD

The present invention relates generally to communications, and more particularly to reverse link loading and reduction of power consumption by remote stations.

Background

The field of wireless communications has many applications including, for example: cordless telephones, paging, wireless local loops, Personal Digital Assistants (PDAs), internet telephones, and satellite communication systems. A particularly important application is cellular telephone systems for mobile subscribers. As used herein, the term "cellular" system encompasses both cellular and Personal Communication Services (PCS) frequencies. Various air interfaces have been developed for such cellular telephone systems including, for example, Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), and Code Division Multiple Access (CDMA). In connection therewith, various native internet standards have been established, including, for example, Advanced Mobile Phone Service (AMPS), Global System for Mobile (GSM) and interim standard 95 (IS-95). IS-95 and its derivative standards IS-95A, IS-95B, ANSI J-STD-008 (commonly referred to as IS-95) and proposed high data rate systems are promulgated by the Telecommunications Industry Association (TIA) and other well known standard entities.

Cellular telephone systems configured in accordance with the uses of the IS-95 standard employ CDMA signal processing techniques to provide efficient and robust cellular telephone service. Exemplary cellular telephone systems configured substantially in accordance with the use of the IS-95 standard are described in U.S. patent nos. 5103459 and 4901307, which are assigned to the assignee of the present invention and incorporated herein by reference. An exemplary system employing CDMA techniques is the CDMA2000 ITU-R Radio Transmission Technology (RTT) candidate proposal (referred to herein as CDMA2000), issued by the TIA. The standard for cdma2000 IS given in the draft of IS-2000 and has been established by the TIA and 3GPP 2. Another CDMA standard is the W-CDMA standard, which is included in the third generation partnership project "3 GPP" under document nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214.

The telecommunication standards cited above are only some examples of the various communication systems that can be implemented. In these various communication systems, multiple users must share system resources. According to the actual system implementation, resource allocations such as bandwidth, time, transmission power, or spreading codes are typically shared by multiple users within the system. In FDMA systems, the system bandwidth is divided into a number of frequency channels, each of which is assigned to a user. In a TDMA system, the system bandwidth is divided into a number of time slots, each of which is assigned to a user. In a CDMA system, system bandwidth is shared simultaneously among all users by using spreading codes, where each user is assigned a spreading code.

User demand drives the design and development of more efficient systems. The present invention addresses this need by allowing remote station(s) to individually employ an improved control-hold mode that reduces the total reverse link load and the power consumption of the remote station. The reverse link comprises the communication channel from the remote station to the base station. The forward link comprises the communication channel from the base station to each remote station operating within range of the base station. A remote station operating in the improved control-hold mode will not monitor or respond to most forward link transmissions from the base station. Thus, when an individual remote station is operating in the improved control-hold mode, the overall load on the reverse link will be reduced.

Furthermore, once the remote station enters the improved control-hold mode, certain processing circuitry used to monitor and respond to the forward link signal will become idle, which immediately and directly affects the power consumption of the remote station. Thus, another benefit of using the improved control-hold mode is an increase in remote station battery life.

SUMMARY

A method and apparatus are presented that address the above-mentioned needs. In one aspect, an apparatus for implementing an improved control-hold mode in a remote station operating in a communication system employing a packet data channel and an associated control channel and an associated feedback channel is provided, comprising: a memory element; and a processor element configured to execute a set of instructions held in the memory element, the set of instructions for: stopping monitoring the packet data channel from the base station; ceasing to monitor a control channel associated with the packet data channel from the base station; closing a reverse link acknowledgement channel; gating off transmissions from the remote station to the base station; and intermittently transmitted over a data control channel.

In another aspect, a method for updating an active set when a remote station is in an improved control-hold mode is presented, the method comprising: transmitting the pilot strength measurements to the base station; receiving a signaling message from a base station; transitioning from an improved control-hold mode to an active mode, wherein said transitioning is triggered by said signaling message; receiving an acknowledgement message with update information from a base station; updating the active set with update information from the base station; and transitioning from the active set to the control-hold mode.

In another aspect, a method for a remote station to switch sectors in a base station when the remote station is in a control-hold mode is provided, comprising: determining whether a channel quality indicator channel is currently gated off; sending a message to a different sector on the channel quality indicator channel if the channel quality indicator channel is not fully gated off; if the channel quality indicator channel is completely gated off: transmitting a signaling message to the base station on the data control channel; receiving a forward link acknowledgement message on a common assignment channel; switching to a different sector; and transmitting a reverse link acknowledgement message on the data control channel.

In another aspect, a method for transitioning from an improved control-hold mode to an active mode is presented, wherein the transitioning is initiated by a remote station, the method comprising: transmitting a signaling message to the base station over the reverse data control channel while in the improved control-hold mode; starting a continuous transmission to the base station on a channel quality indicator channel; beginning to monitor a forward packet data channel and an associated control channel; receiving an acknowledgement signal over a forward packet data channel; and starting reverse link transmission in the active mode.

In another aspect, a method for transitioning a remote station from an improved control-hold mode to an active mode, wherein the transitioning is initiated by a base station, is presented, the method comprising: transmitting a signaling message to the remote station over the forward common assignment channel, whereby the signaling message is repeatedly transmitted until an acknowledgement signal is received from the remote station; transmitting an acknowledgement message from the base station to the remote station over a reverse data control channel; activating at least two feedback channels at the remote station; and initiating monitoring of the forward packet data channel and associated control channel at the remote station.

Brief Description of Drawings

Fig. 1 is a diagram of a wireless communication network.

Fig. 2 is a flow chart of a handoff procedure for a remote station in an improved control-hold mode.

Fig. 3 is a flow chart of an inter-BTS cell handover procedure for a remote station in an improved control-hold mode.

Fig. 4 is a flow chart for transitioning from the improved control-hold mode to the active mode, where the process is initiated by the remote station.

Fig. 5 is a flow chart for transitioning from the improved control-hold mode to the active mode, where the process is initiated by the base station.

Detailed Description

As shown in fig. 1, a wireless communication network 10 generally includes a plurality of mobile stations (also referred to as remote stations, subscriber units, or user equipment) 12a-12d, a plurality of base stations (also referred to as Base Transceiver Stations (BTSs) or node bs) 14a-14c, a Base Station Controller (BSC) (also referred to as a radio network controller or packet control function 16), a Mobile Switching Center (MSC) or switch 18, a Packet Data Serving Node (PDSN) or internetworking function (IWF)20, a Public Switched Telephone Network (PSTN)22 (typically a telephone company), and an Internet Protocol (IP) network 24 (typically the internet). For simplicity, four mobile stations 12a-12d, three base stations 14a-14c, one BSC 16, one MSC 18, and one PDSN 20 are shown. Those skilled in the art will appreciate that there may be any number of mobile stations 12, base stations 14, BSCs 16, MSCs 18, and PDSNs 20.

In one embodiment, the wireless communication network 10 is a packet data service network. The mobile stations 12a-12d may be one of a number of different types of wireless communication devices such as a portable telephone, a cellular telephone that is connected to a laptop computer running an IP-based Web browser application, a cellular telephone with an associated hands-free car kit, a Personal Data Assistant (PDA) running an IP-based Web browser application, a wireless communication module incorporated into a portable computer, or a fixed location communication module such as might be found in a wireless local loop or meter reading system. In the most general embodiment, the mobile station may be any type of communication unit.

The mobile stations 12a-12d may preferably be configured to implement one or more wireless packet data protocols, such as those described in the EIA/TIA/IS-707 standard. In particular embodiments, mobile stations 12a-12d generate IP packets directed to IP network 24 and encapsulate these IP packets within frames using a point-to-point protocol (PPP).

In one embodiment, the IP network 24 is coupled to the PDSN 20, the PDSN 20 is coupled to the MSC 18, the MSC 18 is coupled to the BSC 16 and the PSTN 22, and the BSC 16 is coupled to the base stations 14a-14c by wireline configured for transmission of voice and/or data packets in accordance with a variety of known protocols, including, for example: e1, T1, Asynchronous Transfer Mode (ATM), IP, PPP, frame relay, HDSL, ADSL, or xDSL. In another embodiment, the BSC 16 is coupled directly to the PDSN 20, while the MSC 18 is not coupled to the PDSN 20.

During typical operation of the wireless communication network 10, the base stations 14a-14c receive and demodulate sets of reverse link signals from various mobile stations 12a-12d engaged in telephone calls, Web browsing, or other data communications. Each reverse link signal received by a given base station 14a-14c is processed within the base station 14a-14 c. Each base station 14a-14c may communicate with a plurality of mobile stations 12a-12d by modulating and transmitting sets of forward link signals to the mobile stations 12a-12 d. For example, as shown in fig. 1, the base station 14a communicates with first and second mobile stations 12a, 12b simultaneously, while the base station 14c communicates with third and fourth mobile stations 12c, 12d simultaneously. The resulting packets are forwarded to the BSC 16, which provides call resource allocation and mobility management functions, including orchestrating soft handoffs of a call for a particular mobile station 12a-12d from one base station 14a-14c to another base station 14a-14 c. For example, a mobile station is communicating with two base stations 14b, 14c simultaneously. Eventually, when the mobile station 12c moves far enough away from one base station 14c, the call will be handed off to another base station 14 b.

If the transmission is a conventional telephone call, the BSC 16 will route the received data to the MSC 18, which provides additional routing services for interfacing with the PSTN 22. If the transmission is a packet-based transmission, such as a data call directed to the IP network 24, the MSC 18 will route the data packet to the PDSN 20, which will send the packet to the IP network 24. Alternatively, the BSC 16 may route the packets directly to the PDSN 20, which sends the packets to the IP network 24.

In some communication systems, packets carrying data traffic are divided into a plurality of subpackets, which occupy slots of a transmission channel. For simplicity of explanation, the nomenclature of a cdma2000 system is used herein. This use is not intended to limit the implementation of the embodiments herein to cdma2000 systems. Embodiments may be implemented in other systems, such as WCDMA, without affecting the scope of the embodiments described herein.

The forward link from a base station to a remote station operating within range of the base station can include multiple channels. Some channels of the forward link may include, but are not limited to: a pilot channel, a synchronization channel, a paging channel, a quick paging channel, a broadcast channel, a power control channel, an assignment channel, a control channel, a dedicated control channel, a Medium Access Control (MAC) channel, a fundamental channel, a supplemental code channel, and a packet data channel. The reverse link from the remote station to the base station also includes multiple channels. Some channels of the reverse link may include, but are not limited to: a pilot channel, a power control channel, an assignment channel, a control channel, a dedicated control channel, a Medium Access Control (MAC) channel, a fundamental channel, a supplemental channel, an acknowledgement channel, and a channel quality indicator channel.

Each channel conveys a different type of information to the destination. In general, voice traffic is communicated over a fundamental channel and data traffic is communicated over a supplemental channel or a packet data channel. The supplemental channel is typically a dedicated channel, while the packet data channel typically conveys signals directed to different recipients in a time and code multiplexed manner. Alternatively, the packet data channel is also described as a common supplemental channel.

Voice traffic and data traffic are typically coded, modulated, and spread prior to transmission on the forward or reverse links. The coding, modulation, and spreading may be implemented in a variety of formats. In a CDMA system, the transmission format ultimately depends on the type of channel over which the voice traffic and data traffic are transmitted, as well as the condition of the channel, which may be described in terms of fading and interference. The transmission parameters may be communicated on one or more separate control channels for occasional transmission or whenever data traffic transmission occurs. The reception of the transmission parameters enables the decoder to quickly reset the decoding and demodulation parameters of a particular internal component to the appropriate settings. Furthermore, the reception of transmission parameters on the control channel means that the decoder does not need to perform time-and resource-consuming calculations for other transmission parameters on the data traffic channel.

In addition to the control channel and the data traffic channel, two feedback channels may be implemented, such as an Acknowledgement (ACK) channel and a Channel Quality Indicator (CQI) channel. The ACK channel in a cdma 20001 xEVDV system is used on the reverse link to directly acknowledge receipt of data sub-packets on the data traffic channel. The ACK channel is Binary Phase Shift Keying (BPSK) modulated with 1 bit (or 0 or 1) indicating whether the subpacket has been accurately decoded. The CQI channel is used to inform the control channel of the need for a new transmission parameters message. The remote station uses the channel quality feedback channel to communicate channel quality measurements for the best serving sector to the base station. Channel quality is measured in terms of a carrier-to-interference (C/I) ratio and is based on the received forward link signal.

In cdma 20001 x systems, a remote station is either in an idle mode, where the remote station is not maintaining a call but is ready to receive a call, or in an active mode, where the remote station is maintaining a call. In active mode, the remote station may enter a divide state known as control-hold mode, where the fundamental channel that would normally operate in active mode would be replaced by a Data Control Channel (DCCH) with a gated reverse link pilot. In this type of control-hold mode, the remote station neither transmits nor receives user data traffic. The remote station transmits or receives signaling messages only on the control channel.

Embodiments of the present invention are directed to an improved control-hold mode that is designed to reduce the processing requirements of a remote station. The improved control-hold mode is a state that the remote station can enter such that the remote station can cease monitoring each forward link channel and cease each reverse link channel without entering an idle mode. Entry into idle mode is undesirable because a remote station entering idle mode must release a communication channel that has been established with the base station. To re-enter the active mode, the remote station may need to re-establish the communication channel, which may be time consuming.

The properties of the improved control-hold mode are as follows:

1. the forward secondary packet data control channel (F-SPDCCH) is not monitored.

2. The forward primary packet data control channel (F-PPDCCH) is not monitored.

3. The Packet Data Channel (PDCH) is not monitored.

4. The forward acknowledgement channel (F-ACKCH) is not monitored.

5. The reverse acknowledgement channel (R-ACKCH) is turned off.

6. The reverse channel quality indicator channel (R-CQICH) is gated off at a system-defined duty cycle, such as 0, 1/16, 1/8, 1/4, and 1/2.

7. The reverse pilot channel (R-PICH) is gated off at a system defined duty cycle.

8. The reverse data control channel (R-DCCH) is maintained in a discontinuous transmission mode.

9. The modified forward common assignment channel (F-CACH) is continuously monitored.

10. Each base station in the active set of the remote station maintains a forward common power control channel (F-CPCCH) subchannel for the remote station. The F-CPCCH subchannel is gated off at the same rate as the reverse link pilot channel (R-PICH).

11. The F-CPCCH and R-PICH are used to maintain a power control loop between the remote station and the base station. Alternatively, the F-CPCCH and R-power control sub-channels are used to maintain a power control loop between the remote station and the base station.

The problem of achieving an improved control-hold mode becomes important due to the intricate interaction between the various data traffic, control and feedback channels in many situations, such as in the case of "handovers" and inter-BTS cell handovers. The term "handoff" refers to the process of updating the "active set" in a remote station. inter-BTS cell handover refers to the process of switching a base station or a serving sector of a BTS with a serving sector of another BTS.

Fig. 2 is a flow chart of a switching process in an improved control-hold mode. The processor and the memory element may be configured to execute instructions for carrying out the switching process. The general practice of performing a handoff identifies the transmission energy levels of the signals (typically pilot signals) received from the candidate base stations, which are then grouped into at least four sets. In these groups, the active set is the set of interest for the embodiments described herein. In idle mode, the active set is the set of serving base stations that contain the remote station. In active mode, the active set is the set of all such base stations: information from these base stations is actively demodulated and decoded by the remote station.

In step 200, the remote station transmits a Pilot Strength Measurement Message (PSMM) on the R-DCCH to the base station.

In step 210, the base station sends a signaling message to the remote station, wherein the signaling message triggers a transition of the remote station from the improved control-hold mode to the active mode. The signaling message should be sent in an assured way, such as might be the case when the resource allocation mini message is sent on the F-CACH.

In step 220, the remote station sends a layer 2 acknowledgement message on the R-DCCH to the base station and transitions from the improved control-hold mode to the active mode.

In step 230, the base station sends a Universal Handoff Direction Message (UHDM) to the remote station on the F-PDCH. UHDM messaging allows a remote station to update the information of the active set.

In step 240, the remote station updates the active set as indicated by the UHDM message and then transitions from the active mode to the improved control-hold mode. The transition time from active mode to modified control-hold mode in this step is a system defined parameter, which is carried by the UHDM message. Alternatively, the transition time may be a predetermined duration of time maintained by the remote station.

In step 250, the remote station sends a signaling message to the base station, wherein the signaling message is used to acknowledge receipt of the UHDM message. In an embodiment, the signaling message may be a handover complete message sent on the R-DCCH.

Fig. 3 is a flow diagram of an inter-BTS cell handover procedure that may be implemented when a remote station is in an improved control-hold mode. A processor and a memory element may be configured to execute instructions for performing the process. In step 300, the remote station determines whether the R-CQICH is fully gated off. If the R-CQICH is not completely gated off, the remote station sends a message to the target BTS on the R-CQICH in step 305.

In step 310, if the R-CQICH is completely gated off, the remote station sends a signaling message on the R-DCCH to the base station with information regarding whether the remote station is ready to switch to a cell of another BTS.

In step 320, the base station sends a signaling message acknowledging the message sent in step 310. The signaling messages may be communicated over the F-CACH.

In step 330, the remote station sends an acknowledgement message on the R-DCCH and switches to the new cell.

The foregoing embodiments describe processes that may be performed by a remote station while in an improved control-hold mode. The following example describes the process that can be implemented to transition out of the improved control-hold mode. In one process, a transition from the improved control-hold mode to the active mode is initiated by the remote station. In another procedure, a transition from the improved control-hold mode to the active mode is initiated by the base station.

Fig. 4 is a flow chart describing a process that may be implemented when a remote station initiates a transition. A processor and a memory element may be configured to execute instructions for performing the process. In step 400, the remote station transmits a signaling message over the R-DCCH.

In step 410, the remote station starts to continuously transmit on the R-CQICH.

In step 420, the remote station starts monitoring the F-SPDCCH and the F-PDCH and turns on the R-ACKCH. In one embodiment, the transmission power of the remote station is set based on a power controlled reverse pilot and a predetermined traffic-to-pilot (T/P) ratio.

In step 430, the base station to which the remote station is directed sends an acknowledgement message to the remote station over the F-PDCH. Alternatively, an acknowledgement message may be sent over the F-CACH, said acknowledgement message containing the medium access control identifier MAC _ ID.

After receiving the acknowledgement from the target base station, the remote station begins transmitting on the reverse link in step 440. If the remote station does not receive an acknowledgement from the base station within the predetermined time period, the remote station retransmits the signaling message using the R-DCCH in step 450.

Fig. 5 is a flow chart illustrating a process for transitioning from the improved control-hold mode to the active mode, which may be implemented when the base station is the initiating party. A processor and a memory element may be configured to execute instructions for performing the process. In step 500, the base station sends a signaling message to the target remote station. The signaling message includes the MAC _ ID and is sent over the F-CACH.

The transmission power of the F-CACH is based on the maintained power control bit power level. As described above, the power control loop between the remote station and the base station is maintained while the remote station is in the improved control-hold mode.

Upon receiving the signaling message, the target remote station sends an acknowledgement message on the R-DCCH in step 510.

In step 520, the remote station turns on the R-CQICH and R-ACKCH and starts monitoring the F-SPDCCH and the F-PDCH.

In step 530, the base station detects the transmission on the newly activated R-CQICH and schedules data transmission to the target remote station accordingly. If the base station does not receive the acknowledgement sent from the remote station in step 510, the base station continues to send signaling messages until such an acknowledgement is received.

Those of skill in the art would understand that information and signals may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the above description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

Those of skill would further appreciate that the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. The skilled person will recognize the interactivity of the hardware and software in these cases and how best to implement the described functionality for each particular application. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

The implementation or execution of the various illustrative logical blocks, modules, and algorithm steps described in connection with the embodiments described herein may be implemented or performed with: a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The steps of a method or algorithm described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of the two. A software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such the processor can read information from, and write information to, the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a subscriber unit. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (5)

1. An apparatus for implementing an improved control-hold mode in a remote station operating in a communication system employing packet data channels with associated control channels and associated feedback channels, the apparatus comprising:

a memory element; and

a processing element for executing a set of instructions held in the memory element, the set of instructions for:

stopping monitoring the packet data channel from the base station;

ceasing to monitor a control channel associated with the packet data channel from the base station;

closing a reverse link acknowledgement channel;

turning off transmission gating from the remote station to the base station; and

intermittently transmitted on a data control channel.

2. A method for updating an active set when a remote station is in an improved control-hold mode, comprising:

sending a pilot strength measurement to the base station;

receiving a signaling message from the base station;

transitioning from the improved control-hold mode to an active mode, wherein the transitioning is triggered by the signaling message;

receiving an acknowledgement message with update information from the base station;

updating the active set with update information from the base station; and

transitioning from the active set to the control-hold mode.

3. A method for a remote station to switch sectors in a base station when the remote station is in a control-hold mode, comprising:

determining whether a channel quality indicator channel is currently gated off;

transmitting a message to a different sector on the channel quality indicator channel if the channel quality indicator channel is not fully gated off;

if the channel quality indicator channel is completely closed:

transmitting a signaling message to the base station on the data control channel;

receiving a forward link acknowledgement message on a common assignment channel;

switching to a different sector; and

transmitting a reverse link acknowledgement message on the data control channel.

4. A method for transitioning from an improved control-hold mode to an active mode, wherein the transition is initiated by a remote station, the method comprising:

transmitting a signaling message to the base station over a reverse data control channel while in the improved control-hold mode;

starting continuous transmission to the base station over a channel quality indicator channel;

beginning to monitor a forward packet data channel and an associated control channel;

receiving an acknowledgement signal over the forward packet data channel; and

reverse link transmission is started in accordance with the active mode.

5. A method for transitioning from an improved control-hold mode to an active mode, wherein the transition is initiated by a base station, the method comprising:

transmitting a signaling message to the remote station over a forward common assignment channel and then repeatedly transmitting the signaling message until an acknowledgement signal is received from the remote station;

transmitting an acknowledgement message from the remote station to the base station over a reverse data control channel;

activating at least two feedback channels at the remote station; and

monitoring a forward packet data channel and an associated control channel begins at the remote station.