US20020067701A1

US20020067701A1 - Advanced access channel methods and systems

Info

Publication number: US20020067701A1
Application number: US09/983,425
Authority: US
Inventors: Xixian Chen; Neil McGowan; Mohammad Islam; Ning Guo; Hong Ren
Original assignee: Nortel Networks Ltd
Current assignee: Nortel Networks Ltd
Priority date: 2000-10-24
Filing date: 2001-10-24
Publication date: 2002-06-06
Also published as: CN1964229A; CN1481626A; DE60126368D1; EP1612969A1; JP2004511995A; EP1612969B1; EP1332568B1; ATE398864T1; CN100490353C; US8897124B2; US8248912B2; DE60134484D1; US7154846B2; BRPI0114892B1; KR100877447B1; ES2281049T3; JP4309129B2; WO2002035735A3; US20030067899A9; DE60126368T2

Abstract

Various embodiments of the invention provide an advanced access channel through which wireless terminals can access an access network. Other embodiments provide a method of performing power control using a shared power control channel. The shared power control channel is also used in conjunction with the advanced access channel to provide an acknowledgement mechanism.

Description

RELATED APPLICATIONS

This application claims the benefit of [0001] provisional application 60/243,013 filed Oct. 24, 2000, provisional application 60/246,889 filed Nov. 8, 2000, 60/250,734 filed Dec. 1, 2000, provisional application 60/266,602 filed Feb. 5, 2001, and provisional application 60/277,951 filed Mar. 23, 2001.

FIELD OF THE INVENTION

The invention relates to CDMA systems, and in particular to channels, methods and systems for performing access in such systems.

BACKGROUND OF THE INVENTION

Recent innovations in wireless communications have seen the proposal of a shared data channel on which multiple wireless terminals can receive data. Details of this are provided in applicants copending application no. [attorney docket 71493-1001] filed the same day as this application hereby incorporated by reference in its entirety.

1xEV-DV is a wireless technology related to 3GPP2 (3rd generation partnership project 2) wireless standardization process. 1xEV-DV technology has been designed to offer wireless operators a cost-effective migration path to provide integrated voice and data speeds up to 5.2 Mbps on a single 1.25 MHz code division multiple access (CDMA) carrier. 1XEV-DV enables real time voice, data and multimedia services on existing cdma2000 networks allowing end users to browse the Internet from a personal computer or access email while “on the go”. 1xEV-DV is a global open standards proposal intended as an orderly migration path beyond IS-2000 1× in order to allow wireless network operators to provide their customers with integrated real-time voice and data at a higher data rate.

In a CDMA system, a reverse link access channel and a forward link control channel are used to exchange signaling information between a Wireless terminal and a Base Station (BS). An effective access channel for accessing the forward traffic channel is required.

IS-2000 introduces an enhanced access channel which can operate in three possible modes: basic access mode, power controlled access mode, and reservation access mode. When operating in the basic access mode, the access channel is not power controlled. In the power controlled access mode and reservation access mode, power control starts only after a power control (PC) bit assignment message from the base station or after a common control channel assignment message from the base station and this does not occur until after a significant delay,

SUMMARY OF THE INVENTION

According to a first broad aspect, the invention provides a method of providing forward shared power control. The method involves transmitting a shared power control channel in which is allocated one power control bit per power control period for each of a plurality of users with the bit being a three state bit, the three states being a zero state, a one state, and a no energy state, each of the three states indicating one of an increase, decrease, or no change to transmit power.

Preferably, the method further involves periodically allocating at least one power control bit for each of the plurality of users which indicates a relative gain adjustment, the relative gain adjustment instructing a change in a gain adjustment applied to at least one channel of the user compared to a gain adjustment applied to at least one other channel of the user.

Preferably, each of the at least one power control bit which indicates a relative gain adjustment is a three state bit, the three states being a zero state, a one state, and a no energy state, each of the three states indicating one of increase in the gain adjustment applied to the one channel over the gain adjustment applied to the at least one other channel, a decrease in a gain adjustment applied to the one channel over the gain adjustment applied to the at least one other channel, or no change to the relative gain to be applied to the one channel over the at least one other channel.

Preferably, the power control bits are transmitted using a unique long code mask.

Preferably, the shared power control channel comprises a plurality of time multiplexed subchannels, with one subchannel being used to transmit power control bits to a given user.

According to another broad aspect, the invention provides a transmitter adapted to perform power control. The transmitter has a signal strength measurement circuit adapted to measure a signal strength indication for a respective signal received from each of a plurality of wireless terminals. The transmitter also has power control circuitry adapted to decide based on the signal strength indication whether to instruct each of the wireless terminals to increase its transmit power, decrease its transmit power, or not to change its transmit power and to transmit a shared power control channel in which is allocated one power control bit per power control period for each of a plurality of wireless terminals with the bit being a three state bit, the three states being a zero state, a one state, and a no energy state, each of the three states indicating one of an increase, decrease, or no change to transmit power.

Preferably, the transmitter is further adapted to transmit relative gain adjustments on the shared power control channel.

According to another broad aspect, the invention provides a wireless terminal having receive circuitry adapted to extract power control bits from a shared power control channel, the power control bits having three possible states, the three states being a zero state, a one state, and a no energy state, and depending upon the a state of a given extracted power control bit to make one of three power control decisions, the three decisions being to increase, decrease, or make no change to a transmit power.

Preferably, the wireless terminal is adapted to maintain a first and second threshold, wherein a received value of an extracted power control bit below the first threshold is interpreted as a first of the three decisions, a received value of an extracted power control bit between the first threshold and the second threshold is interpreted as a second of the three decisions, and a received value of an extracted power control bit greater than the second threshold is interpreted as the third of the three decisions.

Preferably, the wireless terminal is further adapted to make dynamic adjustments to the first threshold and the second threshold as a function of a signal to noise ratio estimated by the wireless terminal.

Preferably, the wireless terminal is further adapted to interpret a subset of the extracted power control bits as adjustments to a relative amount by which the transmit power is increased and/or decreased for one transmit channel compared to another transmit channel upon receipt of an appropriate power control bit.

According to another broad aspect, the invention provides a system adapted to facilitate an access probe from a wireless terminal in which power control commands are transmitted to the wireless terminal during a preamble portion of the access probe.

In the system, preferably, power control commands sent during the preamble portion of the access probe are treated as an implicit acknowledgement by the wireless terminal. Preferably, power control commands are transmitted to the wireless terminal after a request portion of the access probe, both to power control the wireless terminal, and to indicate acceptance of requested parameters in the request portion of the access probe.

Another broad aspect of the invention provides a method of accessing a wireless access network. The method involves a first wireless terminal sending an access probe which comprises an initial preamble, a request message and a data content. Preferably, a predetermined long code mask is allocated for the use of transmitting access probes by a plurality of wireless terminals including said first wireless terminal, the predetermined long code mask having a time-dependent field which can take on one of a plurality M of values, thereby allowing up to M independent overlapping access probes each starting at a different time offset, thereby defining M access sub-channels.

Preferably, the method further involves the first wireless terminal selecting an access sub-channel for use in transmitting the access probe as a function of a time at which a user initiated the access probe.

The method preferably further involves the first wireless terminal looking for power control information from a base station in respect of the access subchannel while transmitting the preamble, and treating such power control information when detected as an implicit acknowledgement of the preamble. The request message and the data message are not sent until the power control information is detected.

Preferably, the method further involves a component of the access network broadcasting information comprising one or more of: an slot duration indicating a size of the time offset between access subchannels; a number M of offsets available corresponding to a number of access subchannels; and a maximum total access probe duration.

Preferably, the method further involves a component of the access network monitoring for a preamble portion of access probes on the access subchannels, and when a preamble portion is detected on a given access subchannel, transmitting power control commands on a power control subchannel associated with the given access subchannel.

Another broad aspect of the invention provides a method of performing an access attempt. The method involves a wireless terminal acquiring time synchronization with the base station. The wireless terminal selects an advanced access subchannel from one of a plurality of time dependent advanced access subchannels based on when the access attempt was initiated. The wireless terminal transmits an access preamble using the selected advanced access subchannel and at the same time monitors the energy of the shared power control subchannel associated with the selected advanced access subchannel. If sufficient energy is detected in the shared power control subchannel associated with the selected advanced access subchannel, the wireless terminal transmits a request message followed by a user data packet, and during this transmission, the wireless terminal continues to monitor the energy of the shared power control subchannel associated with the selected advanced access subchannel. If the energies detected while transmitting the request message or during an initial portion of user data packet become insufficient, the wireless terminal aborts the transmission. The wireless terminal controls a transmit power as a function of power control commands received on the shared power control subchannel associated with the selected advanced access subchannel.

Preferably, as soon as a wireless terminal receives an acknowledgement of the preamble and starts to transmit the request message, the wireless terminal begins to transmit power control commands to the base station on a pilot channel transmitted by the wireless terminal to control the power of the shared power control subchannel on the forward link, for example as per power control bits transmitted in 1xRTT to power control the forward traffic channel.

In another embodiment, prior to transmitting the preamble, the wireless terminal monitors an energy of a shared power control subchannel associated with the selected advanced access subchannel, and if there is energy measured in the shared power control subchannel, the wireless terminal determines that this channel is being used by an another wireless terminal, and waits a random back off time before transmitting the preamble on another advanced access subchannel.

Another broad aspect of the invention provides an access network component adapted to acknowledge an access attempt received on an access sub-channel by immediately starting to transmit power control commands on a power control subchannel in one-to-one correspondence with the access sub-channel.

Preferably, the access network component is further adapted to receive request parameters as part of the access attempt, and to acknowledge/grant the request parameters by continuing to send power control commands on the power control subchannel, and to deny the request parameters by ceasing to send any energy on the power control subchannel.

Another broad aspect of the invention provides a wireless terminal adapted to access an access network by sending an access probe which comprises an initial preamble, a request message and a data content. Preferably, the wireless terminal is adapted to use a predetermined long code mask allocated for the use of transmitting access probes, the predetermined long code mask having a time-dependent field which can take on one of a plurality M of values, thereby allowing up to M independent overlapping access probes each starting at a different time offset, thereby defining M access subchannels.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in further detail with reference to the attached drawings in which: [0032]
FIG. 1 is a schematic showing an access channel set by which advanced access is achieved in accordance with an embodiment of the invention; [0033]
FIG. 2 is an example of a long code mask applied to access channel probes; [0034]
FIG. 3 is an example of the time offset of different advanced access subchannels, and also shows associated power control subchannels; [0035]
FIG. 4 is a table showing an example advanced access channel modulation parameters; [0036]
FIG. 5 is an example of a long code mask applied to a shared power control channel; [0037]
FIG. 6 is a flowchart of a method by which a wireless terminal transmits an advanced access probe; [0038]
FIG. 7 is a timing diagram showing an example of two access attempts; [0039]
FIG. 8 is a schematic diagram of a detailed example implementation of the advanced access channel structure implemented by a wireless terminal; [0040]
FIG. 9 is a schematic diagram of a detailed example implementation of the SHPCCH channel structure by a basestation; [0041]
FIG. 10 illustrates gain determination at a base station, and power control bit interpretation at a wireless terminal; and [0042]
FIG. 11 illustrates a relative gain adjustment power control bit. [0043]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIG. 1, shown is a portion of a wireless communications network which will be used to describe an embodiment of the invention by way of example, featuring an [0044] access network 10 serving several wireless terminals 12, only one shown. The access network 10 typically includes a number of base stations (not shown) each having a respective coverage area (not shown). The base stations may provide coverage in sectorized manner to increase frequency reuse. For the purpose of this description, access network 10 is whatever equipment is required for the receipt and processing of the access attempts by a given wireless terminal, such as wireless terminal 12.
Referring to FIG. 1, an embodiment of the invention provides an access channel set generally indicated by [0045] 15 of channels are made use of by wireless terminals in attempting to access the resources of the access network 10, such as fundamental channels, supplemental channels, shared channels, etc. In one embodiment of the invention, the access channel set 15 includes a subset of channels which will be referred to herein as the “Reverse Advanced Access Channel”, or R-AACH 11. The R-AACH 11 is used by a wireless terminal 12 in a wireless cellular communications network to initiate communication with the access network 10 or to respond to a wireless terminal directed message. Referring again to FIG. 1, the R-AACH 11 consists of a Reverse Pilot Channel or R-PICH 16 transmitted by the wireless terminal 12, and a Reverse Advanced Access Data Channel or R-AADCH 18 also transmitted by a wireless terminal.
The access channel set [0046] 15 also involves interaction of two further channels, namely a forward shared power control channel, or F-SHPCCH 20 transmitted by the access network 10 in the coverage area of the access network within which the wireless terminal 12 is located, and a forward supplementary paging channel or F-SPCH 22 also transmitted by the access network 10. F-SPCH is a broadcast channel, while the F-SHPCCH sends power control bits to specific wireless terminal in TDMA fashion, i.e. it sends a power control bit to a specific wireless terminal at one time and to another wireless terminal at another time, as described in detail below.
By way of overview, access attempts are made by a [0047] wireless terminal 10 using the R-AACH 11. During access attempts, the F-SHPCCH 20 is used to control the power of the R-AACH. As will be described in detail below, the SHPCCH 20 also serves as an implicit signal for a wireless terminal 12 making the access attempt to go ahead with the transmission of a message part. The base station 10 broadcasts R-AACH related parameters in an advanced access parameters message on the F-SPCH 22. While two channels from the base station 12 are provided in the preferred embodiment, more generally any number of channels (one or more) are required which are capable of providing the wireless terminal 10 with the required access parameters and the required power control information.
One transmission on the R-[0048] AACH 11 or one access attempt will be referred to herein as an advanced access probe (AAP) which uses both the R-PICH 16 and the R-AADCH 18. An advanced access probe has a preamble followed by an access request mini-message which is then followed by actual access data. The preamble is a non-data bearing portion of the advanced access probe sent by the wireless terminal 10 to assist the base station 12 in initial acquisition and channel estimation. During the preamble transmission period, only the R-PICH 16 is transmitted. On the pilot channel, a long code associated with the time (and equivalently with the advanced access subchannel used or the attempt) at which the wireless terminal is mating the access attempt is applied to a short code PN sequence. During the access request mini-message and data transmission, both the R-PICH 16 and the R-AADCH 18 are used. During the advanced access probe, as will be detailed below, the transmit power of the wireless terminal 10 is controlled by the base station 12 via the F-SHPCCH 20. Preferably, the R-PICH 16 is also used to transmit power control commands to the base station during the access request mini-message and data message as described in further detail below.
More specifically, in a preferred embodiment, the initial preamble consists only of the R-[0049] PICH 16; this is followed by a request mini-message during which R-PICH 16 transmissions occur, and transmissions on the R-AADCH 18 at 9.6 kbps occur for 2.5 ms; this is followed by access data during which R-PICH 16 is being transmitted, and the R-AADCH 18 is transmitting at one of the following rates: 9.6 kbps, 19.2 kbps or 38.4 kbps. Preferably a frame duration of 20 ms is employed. The R-AACH 11 preferably uses a random-access protocol. The random-access protocol is used in CDMA systems to deal with the collisions of the access probes initiated by multiple wireless terminals. If the access attempt is not successful, the wireless terminal will back off for a back off time, the back off time being randomly generated by the wireless terminal, and then try its access probe again after the random back off time.
After the preamble is acquired by the [0050] access network 10, immediately the access network 10 starts transmitting power control commands on the F-SHPCCH 20 to control the power of the wireless terminal 12 which is making the advanced access probe. The wireless terminal 12 looks for these power control commands and treats them as an implicit acknowledgement of the advanced access probe. Upon reception of acknowledgement from the access network 10 that the preamble is acquired (i.e. upon detection of power control commands being sent from the access network to the wireless terminal 12 in respect of the advanced access probe), the accessing wireless terminal 12 sends an access request mini-message on the R-AADCH 18, preferably at a fixed rate of 9.6 kbps.
The R-[0051] AACH 11 has defined for it an associated set of transmission slots defined in detail below. For each advanced access probe, the wireless terminal 12 uses one of the transmission slots by using a long code mask associated with the transmission slot and uses this mask until transmission of the advanced access probe is complete. The long code mask is a 42 bit long code mask which is applied to the AACH. The long code mask has a time-dependent field which in one embodiment can take a value from 0 to 5 thereby providing six reverse advanced access subchannels (R-AASCHs). This allows up to 6 overlapping AACH probes each starting at a different time offset. The access channel slot duration is preferably chosen such that there is no long code overlap. This requires that the slot duration multiplied by the number of R-AASCHs must be greater than the maximum probe duration.
Referring now to FIG. 2, an example of a 42 bit long code mask is shown. When transmitting on the advanced access channel using the common long code, the mask is preferably defined to contain 42 bits, referred to herein as M[0052] 00 to M41, as follows: bits M41 through M33 are preferably set to a fixed sequence, for example ‘110001011’ which identifies the long code mask to be that of the advanced access channel; bits M32 through M28 are set to the Advanced Access Channel number; bits M27 through M25 are set to the time-dependent SLOT_OFFSET field; bits M24 through M9 are set to a BASE_ID for a current base station (the base station which transmitted the access channel parameters received by the wireless terminal 12 prior to making the access attempt); and bits M8 through M0 are set to the PN offset of the current base station.
The five bits M[0053] 28-M32 may be used to identify one of multiple advanced access channels, and the three bits M25 to M27 identify a subchannel on the advanced access channel thus identified. Different numbers of bits used for the access channel identifier and for the advanced access subchannel identifier would change the number of advanced access channels, and/or the number of advanced access subchannels which could be identified using the scheme.
The Advanced Access Channel probe duration is (AACH_PREAMBLE_DURATION (the duration of the preamble of the advanced access probe)+request mini-message duration +AACH_DATA_DURATION (the duration of the data portion of the advanced access probe) all preferably in 1.25 ms units. Wireless terminals are assumed to have an accurate representation of system time. An Advanced Access Channel slot for a given wireless terminal begins only at a system time t such (t mod AACH_SLOT_DURATION)=0 where t is the system time in 1.25-ms slots. In other words, the wireless terminal initiates transmission of an advanced access probe on an advanced access channel slot boundary. [0054]
To assist the [0055] wireless terminal 12 in knowing how to generate an advanced access probe, the following information is sent on the F-SPCH 22 by the current base station:
the slot duration (AACH_SLOT_DURATION); [0056]
the number of offsets (NUM_AACH_OFFSET) - this will define the number of R-AASCHs; [0057]
the total probe duration that includes preamble (AACH_PREAMBLE_DURATION), request mini-message length (fixed), and the data message duration (AACH_DATA_DURATION). [0058]
All of these parameters are specified in 1.25 ms units. [0059]
As an example, let's assume the following parameter values, all in 1.25 ms units: [0060]
AACH_SLOT_DURATION=16; [0061]
NUM_AACH_OFFSET=4; [0062]
AACH_PREAMBLE_DURATION=16; [0063]
AACH_DATA_DURATION=46. The total advanced access probe duration in this case will be 16+2+46=64 1.25 ms units. Access probes can start at system times which are integer multiples of the access channel offset. The “offset” field of long code mask of FIG. 2 is computed from the above information as follows: [0064]
floor (t / AACH_SLOT _DURATION) mod NUM_AACH_OFFSET where floor(x) is the largest integer which is smaller than or equal to x. [0065]
FIG. 3 shows how the advanced access subchannels would be separated in time for the above example parameters. Advanced access probes using the first advanced access subchannel will have a slot offset of zero and will last for 64 1.25 ms units as indicated generally at [0066] 30. These advanced access probes can be initiated at any system time t=64×N in 1.25 ms units for any N>=0. The long code used by a wireless terminal transmitting on this access subchannel will identify the subchannel as being the first subchannel by an appropriate setting of the time dependent part (see FIG. 2).
Advanced access probes using the second advanced access subchannel will have a slot offset of one and will last for 64 1.25 ms units, as indicated generally at [0067] 32. These advanced access probes can be initiated at any system time t=(64×N+16) in 1.25 ms units for any N>=0. The long code used by a wireless terminal transmitting on this access subchannel will identify the subchannel as being the second subchannel by an appropriate setting of the time dependent part.
Advanced access probes using the third advanced access subchannel will have a slot offset of two and will last for 64 1.25 ms units as indicated generally by [0068] 34. These advanced access probes can be initiated at any system time t=(64×N+32) in 1.25 ms units for any N>=0. The long code used by a wireless terminal transmitting on this access subchannel will identify the subchannel as being the third subchannel by an appropriate setting of the time dependent part.
Finally, advanced access probes using the fourth advanced access subchannels will have a slot offset of three and will last for 64 1.25 ms units as indicated generally by [0069] 36. These advanced access probes can be initiated at any system time t=(64×N+48) in 1.25 ms units for any N>=0. The long code used by a wireless terminal transmitting on this access subchannel will identify the subchannel as being the first subchannel by an appropriate setting of the time dependent part.
FIG. 4 summarizes in detail the Advanced Access Channel modulation parameters for spreading [0070] rate 1. Spreading rate 1 is 1.2288 Mcps (1.25 MHz channel).
Each advanced access subchannel is associated with a respective shared power control subchannel transmitted as part of the F-SHPCCH ([0071] 20 of FIG. 1). Preferably, there is fixed one-to-one correspondence between the shared power control subchannels and the advanced access subchannels. Hence, there is no need to provide this mapping to the wireless terminal.
More specifically, the Shared Power Control Channel (F-SHPCCH) is used by the base station to transmitting power control commands for the power control of each subchannel of the R-AACH as well as to indicate an implicit acknowledgement to the preamble and request parts of an advanced access probe. Multiple shared power control subchannels (SHPCSCH) are time multiplexed on the SHPCCH. As indicated previously, there is a one-to-one relationship between a SHPCSCH and an AASCH. Up to six wireless terminals using six respective AASCH can be simultaneously power controlled at 800 Hz (one command per 1.25 ms). [0072]
In a preferred embodiment, the channel structure for the Shared Power Control Channel is the same as the Forward Common Power Control Channel structure provided in IS-2000A. [0073]
FIG. 9 (described in detail below) shows a detailed example implementation. [0074]
In another embodiment of the SHPCCH, the SHPCCH is spread with Walsh code W33512. The subchannel positions are randomized with respect to time so that higher power PC bits do not consistently and systematically coincide. A long code mask such as indicated in FIG. 5 is employed. The long code mask contains a three bit field, in the illustrated example bits [0075] 26 to 28 set to 101, which is unique to the F-SHPCCH. A detailed discussion of the actual power control commands transmitted on the F-SHPCCH is presented further below.
The power control commands are sent on the F-[0076] SHPCCH 20 that is designated for the R-AACH 11. There are multiple sub-channels in the F-SHPCCH 20. There is one-to-one relationship between a F-SHPCCH 20 subchannel and an advanced access slot offset. An example of this one-to-one relationship is shown in FIG. 3 for the previously described parameter set example. In this case, there are four advanced access subchannels and associated slot offsets, and there are four shared power control subchannels, labelled SHPCSCH 0 for slots 30 with offset 0, SHPCSCH 1 for slots 32 with offset 1, SHPCSCH 2 for slots 34 with offset 1, SHPCSCH 3 for slots 36 with offset 3.
The presence of power in a shared power control subchannel serves as an implicit acknowledgement to the corresponding advanced access subchannel. Access data is transmitted on the reverse Advanced Access Data Channel (R-[0077] AADCH 18 of FIG. 1) at a fixed data rate of 9.6, 19.2 or 38.4 kbps upon receiving this implicit acknowledgement from the base station. The data rate is based on what the base station is broadcasting as allowable rates and the size of the message. The frame duration for the Advanced Access data on the Advanced Access Channel may be 20 ms in duration. The Advanced Access Data Channel preferably is spread with an 8-ary Walsh cover. More specifically, the Walsh cover (++−−++−−) is preferably used.
The access data may be a message requesting a resource or user data (such as a short message) to be passed on to a defined destination. [0078]
The procedure for the wireless terminal to initiate the advanced access will now be described with reference to the flowchart of FIG. 6. The advanced access probe might be initiated by a user pressing a “call” button on the wireless terminal for example. [0079]
At step [0080] 6-1, when the wireless terminal acquires the synchronization with the base station through the forward link SYNC channel, it selects an advanced access subchannel as a function of the time at which the advanced access probe was initiated. The advanced access subchannel starting on the next slot boundary is selected.
At step [0081] 6-2 the wireless terminal begins to transmit the access preamble using the selected advanced access subchannel and at the same time monitors the energy of the shared power control subchannel associated with the selected advanced access subchannel.
At step [0082] 6-3, if sufficient energy in the shared power control subchannel is detected, (for example if the energies in three consecutive PCBs (power control bits) are above a threshold), the wireless terminal knows that its preamble was acquired by the base station and goes to step 6-5. On the other hand, if insufficient energy detected (for example if for a certain time, no energies in three consecutive PCBs are above the threshold), the wireless terminal knows that its access request was not acquired and/or granted by the base station and goes back to step 6-1, having aborted that particular access attempt, after applying a random back off time (delay) in step 6-4. Also, at step 6-3, the wireless terminal uses the power control commands received on the shared power control subchannel to control the power of the transmission of the preamble portion of the advance access probe.
At step [0083] 6-5, the wireless terminal begins to transmit the request mini-message followed by the user data packet and preferably also begins to transmit power control commands on the reverse pilot channel to start power controlling the shared power control subchannel. During this transmission, the wireless terminal continues to monitor the energy of the shared power control subchannel and will abort the transmission (and return to step 6-1) if power control commands cease to be received, for example, it the energies in three consecutive PCBs are below the threshold. Also, the wireless terminal uses the power control commands received on the shared power control subchannel to control the power of the transmission of the request and data portions of the advance access probe.
Preferably, the request mini-message is sent at 9.6 kbps and lasts for 2.5 ms, and the message fields are as follows: [0084]
a) Requested Rate (2 bits): indicates a requested rate; [0085]
b) Requested Service Type (3 bits): [0086]
Signaling on AACH-only [0087]
SMS or SDB on AACH-only [0088]
voice [0089]
Real-time data on forward and/or reverse link [0090]
Non real-time data on forward and/or reverse link [0091]
c) Wireless terminal-specific Hash code (5 bits) [0092]
d) CRC (8 bits) [0093]
e) Tail bits (6 bits) [0094]
Referring to FIG. 7, a pictorial example of an advanced access procedure will be described. At time T0, a first user wireless terminal initiates an advanced access probe generally indicated by [0095] 50 on the first advanced access subchannel, labelled AACH_1. To would need to be one of the times at which an advanced access probe on the first advanced access subchannel is allowed to start. Shown are time intervals during which the preamble 52, request 54 and data portions 56 of the advanced access probe are transmitted. Generally indicated at 60 is the forward shared power control channel F-SHPCCH. SHPCCH-1 62 is the shared power control subchannel for the first advanced access subchannel. Before the end of the preamble 52 of the advanced access probe, SHPCCH-1 is active which serves as an acknowledgement of the preamble. For the remainder of the advanced access probe 50, the SHPCCH-1 remains active, and the first advanced access probe's request is granted.
At time T1, a second user wireless terminal initiates an advanced access probe generally indicated by [0096] 70 on the second advanced access subchannel, labelled AACH_2. T1 would need to be one of the times at which an advanced access probe on the second advanced access subchannel is allowed to start. Shown are time intervals during which the preamble 72, request 74 and data portions 76 of the advanced access probe are transmitted. SHPCCH-2 64 is the shared power control subchannel for the second advanced access subchannel. Before the end of the preamble 72 of the advanced access probe, SHPCCH-2 is active which serves as an acknowledgement of the preamble. However, during the data transmission, the SHPCCH-2 goes inactive indicating that the request is denied. The transmission is aborted at that time.
In another embodiment, if the total access probe duration is allowed to be greater than the number of offsets multiplied by the slot duration, then there exists the potential for long code overlap. To deal with this, before transmitting the preamble, the wireless terminal may monitor the energy of the shared power control subchannel associated with the selected Advanced Access subchannel. If there is energy measured in the shared power control subchannel, the wireless terminal will know that this channel is being used by an another wireless terminal. The wireless terminal would then wait a random back off time before trying again. [0097]
FIG. 8 is an example implementation of the AACH channel structure. [0098]
FIG. 9 is an example implementation of the SHPCCH channel structure which is based on the structure of the IS2000A CPCCH (common power control channel). In the preferred implementation, there are 2N (N=12, 24, 48) common power control subchannels, numbered from 0 through 2N - 1, in one common power control group of the Common Power Control Channel. These are divided equally between the I arm and the Q arm of the Common Power Control Channel. The MUX blocks [0099] 100,102 in FIG. 9 are used to time division multiplex the N power control bits for the I arm or Q arm. The positions of the N power control bits are randomized by a randomizer 104. After signal mapping 106,108 and gain adjustment 112,114 the power control bits are spread by a Walsh function 116 and then fed through a complex multiplier 118.
Details of the actual usage of PCBs in the shared power control channel will now be described. In a preferred implementation of this channel provided by an embodiment of the invention, a three state power control bit is used on the SHPCCH to control the R-AACH. The power control bits sent to a given wireless terminal are the normal two state bits until after their acknowledgement function is complete, i.e. after acknowledgement of the request message. Preferably, in another embodiment, the three state power control bits can be also used to control the power of reverse data and voice channels such as Fundamental Channels (R-FCH) and Supplemental Channels (R-SCH). A medium value is added to the reverse link power control bit (PCB). Instead of having only 2 possible values (+1, −1), there will be 3 possible values (+1, 0, −1) for the PCB. When used with the R-AACH the ‘0’state is used for a negative acknowledge up until a 20 msec frame of data has been received on the R-AACH. [0100]
When a two value PCB is employed, even when the measured Eb/No level (or other suitable signal quality measurement) is very close to a target value, the wireless terminal will still adjust the output power since there is no way to signal a no-change condition. The result is that either the interference to the other users is increased and battery power is wasted (when the output power is adjusted above the target) or the reverse link Eb/No is degraded (when the output power is adjusted below the target). [0101]
By adding a no-change state (value 0), the resolution of the PCB is increased. The capacity will be increased with the same averaged Eb/No. [0102]
Nominally, when the relative gain of the various channels (pilot, supplementary, fundamental etc.) are set, the power ratio remains constant meaning that if a power control bit is being applied to multiple channels, the power of all channels is adjusted by an equal amount. In a preferred embodiment of the invention, a subset of the power control bits, for example one of every 64 power control bits, are allocated to serve as a relative gain adjustment bit which adjusts the relative amount by which the power of one or more channels is adjusted compared to the pilot channel. For example, the relative gain adjustment bit may be used to control the relative gain applied to the supplementary channel compared to the pilot channel. Multiple such “relative gain adjustment channels” may be provided. [0103]
Referring now to FIG. 10 which shows details of the use of the three value power control bit. The base station transmits +1 (actually a 0 or a 1) to instruct an increase in power, −1 (actually a 1 or a 0) to instruct a decrease in power, and transmits a 0 (transmits zero energy by setting the gain of the PCB bit to zero so that no energy is transferred to the PCB) to instruct no change in the power. [0104]
Preferably, as soon as a wireless terminal receives an acknowledgement of the preamble and starts to transmit the request message, the wireless terminal begins to transmit power control commands to the base station on a pilot channel transmitted by the wireless terminal to control the power of the shared power control subchannel on the forward link, for example as per power control bits transmitted in 1xRTT to power control the forward traffic channel. When traffic channel(s) are present, the power control subchannel will have its gain adjusted based on channel estimates reported by the wireless terminal. Preferably, the power control commands transmitted to the base station are two state power control commands. [0105]
Two PCB thresholds, Threshold_High and Threshold_Low are established for the wireless terminal in respect of the power control bits received. When a received value of a power control bit is greater than Threshold_High, the wireless terminal will increase the output power; when the a received value of a power control bit is smaller than Threshold_Low, the wireless terminal will decrease the output power; and when the detected power is between the Threshold_High and Threshold_Low, the wireless terminal will not change the output power. The thresholds are preferably dynamically determined as a function of a signal to Noise ratio estimated by the wireless terminal. The received values of the power control bits are real values. [0106]
Preferably, as shown in FIG. 11, one of every 64 PCB is a relative gain adjustment. The bit will have 3 values as well. The value of this bit will be determined by the measurement of CRC and the energy of the channels. A “1” in this relative gain adjustment bit will indicate to the wireless terminal to increase the reverse supplemental channel gain (relative to the reverse pilot channel gain) by a certain amount. A “0” indicates no change in the reverse supplemental channel gain (relative to the reverse pilot channel gain), A “−1” indicates to the wireless terminal to decrease the reverse supplemental channel gain (relative to the reverse pilot channel gain) by a certain amount. [0107]
Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. [0108]

Claims

We claim:

1. A method of providing forward shared power control comprising:

transmitting a shared power control channel in which is allocated one power control bit per power control period for each of a plurality of users with the bit being a three state bit, the three states being a zero state, a one state, and a no energy state, each of the three states indicating one of an increase, decrease, or no change to transmit power.

2. A method according to claim 1 further comprising:

periodically allocating at least one power control bit for each of the plurality of users which indicates a relative gain adjustment, the relative gain adjustment instructing a change in a gain adjustment applied to at least one channel of the user compared to a gain adjustment applied to at least one other channel of the user.

3. A method according to claim 2 wherein each of the at least one power control bit which indicates a relative gain adjustment is a three state bit, the three states being a zero state, a one state, and a no energy state, each of the three states indicating one of increase in the gain adjustment applied to the one channel over the gain adjustment applied to the at least one other channel, a decrease in a gain adjustment applied to the one channel over the gain adjustment applied to the at least one other channel, or no change to the relative gain to be applied to the one channel over the at least one other channel.

4. A method according to claim 1 wherein further comprising;

transmitting the power control bits using a unique long code mask.

5. A method according to claim 4 wherein the shared power control channel comprises a plurality of time multiplexed subchannels, with one subchannel being used to transmit power control bits to a given user.

6. A transmitter adapted to perform power control comprising:

signal strength measurement circuit adapted to measure a signal strength indication for a respective signal received from each of a plurality of wireless terminals;

power control circuitry adapted to decide based on the signal strength indication whether to instruct each of the wireless terminals to increase its transmit power, decrease its transmit power, or not to change its transmit power and to transmit a shared power control channel in which is allocated one power control bit per power control period for each of a plurality of wireless terminals with the bit being a three state bit, the three states being a zero state, a one state, and a no energy state, each of the three states indicating one of an increase, decrease, or no change to transmit power.

7. A transmitter according to claim 6 further adapted to transmit relative gain adjustments on the shared power control channel.

8. A wireless terminal comprising:

receive circuitry adapted to extract power control bits from a shared power control channel, the power control bits having three possible states, the three states being a zero state, a one state, and a no energy state, and depending upon the a state of a given extracted power control bit to make one of three power control decisions, the three decisions being to increase, decrease, or make no change to a transmit power.

9. A wireless terminal according to claim 8 further adapted to maintain a first and second threshold, wherein a received value of an extracted power control bit below the first threshold is interpreted as a first of the three decisions, a received value of an extracted power control bit between the first threshold and the second threshold is interpreted as a second of the three decisions, and a received value of an extracted power control bit greater than the second threshold is interpreted as the third of the three decisions.

10. A wireless terminal according to claim 9 further adapted to make dynamic adjustments to the first threshold and the second threshold as a function of a signal to noise ratio estimated by the wireless terminal.

11. A wireless terminal according to claim 8 further adapted to interpret a subset of the extracted power control bits as adjustments to a relative amount by which the transmit power is increased and/or decreased for one transmit channel compared to another transmit channel upon receipt of an appropriate power control bit.

12. A system adapted to facilitate an access probe from a wireless terminal in which power control commands are transmitted to the wireless terminal during a preamble portion of the access probe.

13. A system according to claim 12 in which the power control commands sent during the preamble portion of the access probe are treated as an implicit acknowledgement by the wireless terminal.

14. A system according to claim 12 in which power control commands are transmitted to the wireless terminal after a request portion of the access probe, both to power control the wireless terminal, and to indicate acceptance of requested parameters in the request portion of the access probe.

15. A method of accessing a wireless access network comprising:

a first wireless terminal sending an access probe which comprises an initial preamble, a request message and a data content.

16. A method according to claim 15 wherein a predetermined long code mask is allocated for the use of transmitting access probes by a plurality of wireless terminals including said first wireless terminal, the predetermined long code mask having a time-dependent field which can take on one of a plurality M of values, thereby allowing up to M independent overlapping access probes each starting at a different time offset, thereby defining M access sub-channels.

17. A method according to claim 16 further comprising:

the first wireless terminal selecting an access sub-channel for use in transmitting the access probe as a function of a time at which a user initiated the access probe.

18. A method according to claim 17 further comprising:

the first wireless terminal transmitting the preamble on a pilot channel, and transmitting the request message and the data message on an advanced access data channel.

19. A method according to claim 18 further comprising:

the first wireless terminal looking for power control information from a base station in respect of the access subchannel while transmitting the preamble, and treating such power control information when detected as an implicit acknowledgement of the preamble.

20. A method according to claim 19 wherein the request message and the data message are not sent until the power control information is detected.

21. A method according to claim 15 further comprising:

a component of the access network broadcasting information comprising one or more of:

an slot duration indicating a size of the time offset between access subchannels;

a number M of offsets available corresponding to a number of access subchannels;

a total access probe duration.

22. A method according claim 21 wherein the information broadcast by the component of the access network is broadcast on a supplementary paging channel.

23. A method according to claim 15 further comprising:

a component of the access network monitoring for a preamble portion of access probes on the access subchannels, and when a preamble portion is detected on a given access subchannel, transmitting power control commands on a power control subchannel associated with the given access subchannel.

24. A method according to claim 19 further comprising:

terminating the access probe before completion in the event no implicit acknowledgement is received.

25. A method of performing an access attempt comprising:

a wireless terminal acquiring time synchronization with the base station;

the wireless terminal selecting an advanced access subchannel from one of a plurality of time dependent advanced access subchannels based on when the access attempt was initiated;

the wireless terminal transmitting an access preamble using the selected advanced access subchannel and at the same time monitoring the energy of the shared power control subchannel associated with the selected advanced access subchannel;

if sufficient energy is detected in the shared power control subchannel associated with the selected advanced access subchannel, the wireless terminal transmitting a request message followed by a user data packet, and during this transmission, the wireless terminal continuing to monitor the energy of the shared power control subchannel associated with the selected advanced access subchannel;

if the energies detected while transmitting the request message or an initial portion of the user data packet become insufficient, the wireless terminal aborting the transmission;

the wireless terminal controlling a transmit power as a function of power control commands received on the shared power control subchannel associated with the selected advanced access subchannel.

26. A method according to claim 25 further comprising:

prior to transmitting the preamble, the wireless terminal monitoring an energy of a shared power control subchannel associated with the selected advanced access subchannel, and if there is energy measured in the shared power control subchannel, the wireless terminal determining that this channel is being used by an another wireless terminal, and waiting a random back off time before transmitting the preamble on another advanced access subchannel.

27. A method according to claim 25 wherein energies detected while transmitting the request message or user data packet are determined to be insufficient if three consecutive expected power control commands are below a threshold.

28. A method according to claim 25 wherein sufficient energy is detected in the shared power control subchannel associated with the selected advanced access subchannel if energies in three consecutive expected power control commands are above a threshold.

29. An access network component adapted to acknowledge an access attempt received on an access sub-channel by immediately starting to transmit power control commands on a power control subchannel in one-to-one correspondence with the access sub-channel.

30. An access network component according to claim 29 further adapted to receive request parameters as part of the access attempt, and to acknowledge/grant the request parameters by continuing to send power control commands on the power control subchannel, and to deny the request parameters by ceasing to send any energy on the power control subchannel.

31. An access network component according to claim 29 further adapted to:

look for access attempts by using a predetermined long code mask, the predetermined long code mask having a time-dependent field which can take on one of a plurality M of values, thereby allowing up to M independent overlapping access probes each starting at a different time offset, thereby defining M access sub-channels.

32. An advanced network component according to claim 31 further adapted to broadcast information comprising one or more of:

a maximum total access probe duration.

33. A wireless terminal adapted to access an access network by sending an access probe which comprises an initial preamble, a request message and a data content.

34. A wireless terminal according to claim 33 adapted to use a predetermined long code mask allocated for the use of transmitting access probes, the predetermined long code mask having a time-dependent field which can take on one of a plurality M of values, thereby allowing up to M independent overlapping access probes each starting at a different time offset, thereby defining M access sub-channels.

35. A wireless terminal according to claim 34 further adapted to transmit the preamble on a pilot channel, and transmit the request message and the data message on an advanced access data channel.

36. A wireless terminal according to claim 34 further adapted to process a received signal, and to look for power control commands in the received signal while transmitting the preamble, and treating such power control information when detected as an implicit acknowledgement of the preamble.

37. A wireless terminal according to claim 36 adapted to send the request message and the data message only after power control commands are detected, and to terminate the access probe before completion in the event no implicit acknowledgement is received.

38. A method according to claim 23 further comprising:

as soon as a wireless terminal receives the implicit acknowledgement of the preamble and starts to transmit the request message, the wireless terminal transmitting power control commands to the base station on a pilot channel transmitted to control the power of the power control subchannel.