Power control protocol for highly variable data rate reverse link of a wireless communication system

(74) Agent

IPR Licensing Inc, 300 Delaware Avenue, Suite 527, DE19801 WILMINGTON, USA

James A Proctor Jr., 440 Mosswood Boulevard, Indialantic, FL 32903-4007, USA Bryn Aarflot AS, PO Box 449 Center, 0104 OSLO

<td> (54)</td><td>Designation</td><td>Method for Power Management of a Highly Variable Data Rate Reverse Connection in a Wireless Communication System</td>

<td> (56)</td><td>cited</td><td></td>

<td></td><td>publications</td><td>NO 20006076 A</td>

<td> (57)</td><td>Summary</td><td></td>

A technique for implementing closed loop power management in a wireless code-shared multi-access (CDMA) system, which assigns dynamically coded channels as needed. The technique maintains a proper power level, even when no traffic channels are assigned, by determining a link quality metric based on received reverse link power. This determination is made in response to a heartbeat signal transmitted at a frequency sufficiently fast to maintain code phase locking, e.g. depending on the expected maximum speed at which the subscriber unit will move.

BASE STATION 170 subscriber

<img file="NO323482B1_D0001.tif" />

INTRODUCTION 430

ERKJ. BY PILOT, SYNC (P, S) FOR REV. MAINTENANCE

<img file="NO323482B1_D0002.tif" />

Heartbeat 435

LQR

<img file="NO323482B1_D0003.tif" />

The growing use of cordless phones and personal computers has led to a similar need for advanced telecommunications services that were previously thought to be intended only for use in specialized applications. In the 1980s, wireless voice communication became available to the broad public through the 5 cellular telephone network. Such services were initially usually considered to be the businessman's exclusive area, due to. expected high subscription costs. The same was also the case for access to remote distributed data networks. Until very recently, only business people and large institutions could afford the necessary computers and access line equipment. As a result of the widespread availability of both technologies, the general population now increasingly wants to access not only networks such as the Internet and private intranets, but also to access such networks wirelessly. This is especially true of users of laptops, laptops, handhelds, personal digital assistants, etc., who would prefer to access such networks without being stuck in a telephone line.

There is still no widely available and satisfactory solution for providing cheap high-speed access to the Internet, private intranets and other networks utilizing the existing, cellular, wireless infrastructure. This situation is most likely the result of several unfortunate circumstances. One thing is that the usual way of providing high-speed data service in a business environment over a wireline network is not easily adaptable to the voice quality service available in most homes or offices. Also, such high-speed standard data services cannot easily be used for efficient transmission over standard cell type cellular wireless handsets. In addition, the existing, cellular network was originally designed just to provide voice services. As a result, the main thrust of current digital wireless communication plans lies in speech, although some plans, such as IS-95B, actually provide a certain degree of asymmetric behavior in order to record data transfer. The data rate of a forward traffic channel for IS-95B may e.g. is adjusted in increments from 1.2 kbps up to 0.6 kbps 3o for so-called Rate Set 1 (speed set 1), and in increments from 1.8 kbps up to

14.4 kbps for Rate Set 2. However, on the reverse link's traffic channel, the data rate is fixed at 4.8 kbps.

Existing systems therefore typically provide a radio channel that can record maximum data rates only in the range of 14.4 kilobits per second (kbps) at its best, in the future. A channel with such a low data rate does not offer direct data transfer rates of 28.8 or higher 56.6 kbps, now commonly available through cheap wiring modems, not to mention even higher speeds, such as 128 kbps, available with ISDN (Integrated Services Digital Network) service integrated digital network equipment. Data speeds at such levels are rapidly becoming the lowest acceptable speeds for such activities as browsing web pages. Other types of data networks that use building blocks at higher speeds, such as the xDSL (Digital Subscriber Line) service, are now also in use in the United States.

io Although such networks were known when the cellular systems were initially put into use, there is usually no possibility of providing higher speed data services over the topologies of the cellular networks. Unfortunately, in wireless environments, access to the channels for many subscribers is expensive, and there is competition for them. Whether multi-access is provided using traditional FDMA (Frequency is Division Multiple Access) that uses analog modulation on a group of radio carriers, or using newer digital modulation plans that allow sharing of a radio carrier using TDMA (Time Division Multiple Access, code division multiple access (CDMA), the nature of the radio spectrum is that it is a medium that is expected to be shared. This is quite unlike the traditional data transfer environment, where the bandwidth of the wires is relatively large and therefore not usually meant to be shared between several.

CDMA multi-access plans are, in theory, generally considered to provide the most efficient use of the radio spectrum. CDMA systems, however, only work well when the power levels of individual transmissions are carefully controlled. Current wireless CDMA systems, such as IS-95B, utilize two different types of power control in the uplink direction to ensure that a signal from a given subscriber unit arriving at the base station does not interfere in a destructive manner with the signals arriving from other subscriber units. In a first process referred to as open loop power

3o control (open loop power control), a rough estimate of the correct power control level is created using the mobile subscriber unit itself. After a call is established and as the mobile phone moves around in a cell, in particular, the path loss between the subscriber unit and the base station will continue to change. The mobile phone continues to monitor the reception effect and to adjust its transmit power. In particular, the mobile unit measures a power level of the forward link signal as it is received from the base station, and it then sets its reverse link power accordingly. Thus, for example, if the reception power level is relatively weak, then the mobile unit assumes that it is relatively far from the base station and increases its power level. The reverse is also the case, in that a signal received at a relatively high level indicates that the mobile unit is relatively close to the base station and should therefore be transmitted with reduced power.

But since the forward and reverse links are at different frequencies, open loop power management is inadequate and too slow to compensate for fast io Rayleigh fading. Since Rayleigh fading is frequency dependent, open loop power control alone cannot compensate for Rayleigh fading completely in CDMA systems.

As a result, closed-loop power control is also used to compensate for power fluctuations. As soon as the mobile unit gains access to an ice traffic channel and begins to communicate with the base station, the base station, in the process of closed loop, constantly monitors the level of received power on the reverse connection. If the connection quality begins to deteriorate, the base station sends a command to the mobile unit via the forward connection, to increase its power level. If the connection quality indicates excessive effect on the reverse delay, the base station commands the mobile unit to lower the power.

In the IS-95B standard, the base station sends such power control commands to the mobile device using a specially coded message sent on a traffic channel on the forward link. These embedded messages contain power control commands in the form of power control bits (PCBs). The degree 25 of power gain and power loss for each bit is nominally specified as + 1dB and -1dB. The mobile unit's response to these power control bits is usually expected to be very fast, to compensate for rapid Rayleigh fading. For this reason, these bits are sent directly over the traffic channel. In particular, certain selected bits from the baseband stream are introduced or punctured into the traffic stream to provide a separate subchannel for power control at a rate of 800 bits per second.

The mobile unit thus receives continuous power control bits for every 1.25 ms, via such bit puncture.

Some optimizations of CDMA data transfer systems have recently been developed. These systems use certain coded phase channel allocation plans, which remove coded phase channels when not in use, and then reassign them to provide more efficient use of the radio spectrum. Ideally, encoded phase channels can be assigned to different connections as quickly as possible, while minimizing the radio frequency signaling required. However, a virtual connection must be kept open between each mobile device and the base station, whether a coded phase channel is in use or not. Otherwise it is necessary e.g. to achieve synchronization again each time a channel is assigned to or removed from a particular connection.

In particular, in the case of attempts to implement closed loop power control signaling, there is unfortunately no active traffic channel in which power control bits can be retrieved for every 1.25 milliseconds. It would be impractical to have to regain the correct power level each time a new code phase channel was assigned.

Therefore, it is desirable to maintain the proper power level on the reverse connection, even when code phase channels are dislocated from a particular connection.

The present invention is a technique for implementing a code-shared multi-access system that dynamically assigns coded traffic channels on a demand basis. This technique maintains a known transmit power level for reverse link channel equipment, even when the subscriber unit has entered standby mode where no traffic channels are active.

This is achieved in standby mode by having the base station measure certain quality parameters for a maintenance heartbeat signal that is periodically transmitted on a reverse channel from a subscriber unit when in standby mode. The heartbeat signal is a minimum signal transmitted at a rate sufficient to maintain code phase lock between the subscriber unit and the base station. The speed at which the heartbeat signals are transmitted depends on the expected maximum speed for physical movement of the subscriber unit. In systems that are expected to support walking-type mobility, the heartbeat signal, e.g. only to be sent every few seconds.

More precisely, according to the present invention, there is provided a method for providing wireless communication with digital signals, wherein the digital signals are communicated between multiple wireless subscriber units and a base station, where the digital signals are communicated using at least one radio frequency channel modulated by radio signals. code-shared multi-access, the digital signals also having a given, Nominal data rate The method of the invention is characterized by the following steps:

(a) multiple subchannels are made available within each CDMA radio channel, where a data rate for each subchannel is much lower than the nominal data rate of the digital signals;

(b) available subchannels are assigned only on demand as the number of subchannels assigned thereby changes over the duration of a given session;

(e) on the reverse link, providing a standby mode connection for subscriber units turned on but not currently transmitting data, standby mode is provided by transmitting a heartbeat signal from the subscriber unit to the base station at a data rate which is fast enough to maintain bit synchronization on the reverse link; and (d) during standby mode, link quality report messages are sent to the subscriber unit.

Advantageous and preferred embodiments of the method according to the invention are set forth in the appended dependent claims 2-9. The link quality parameters are preferably a measurement of bit error rate, but may also be a noise level measurement, or a signal power level measurement.

The link quality information is then sent from the base station to the subscriber unit, usually formatted! as a link quality report message. The link quality reports are sent on a forward connection dialing channel or synchronization channel to a subscriber unit which is in standby mode.

The subscriber unit then uses the link quality information as a parameter for a logical decision circuit or function that finally determines the transmit power level of the associated reverse connection.

The foregoing and other objects, features and advantages of the invention will become apparent from the following, more specific description of preferred embodiments of the invention, as illustrated in the accompanying drawings, in which the same reference numerals refer to the same parts in the various figures.

Fig. 1 is a block diagram of a wireless communication system utilizing a bandwidth management system according to FIG. invention.

Fig. 2 is a diagram showing how subchannels are mapped within a given radio frequency channel for a forward connection.

Fig. 3 is a diagram showing how subchannels are mapped within a given RF channel with a reverse connection.

s Fig. 4 is a state diagram of a connection quality messaging system according to FIG.

invention.

Referring now to the drawings, FIG. 1 is a block diagram of a system 100 for providing high speed data and voice service over a wireless connection, by seamlessly integrating a digital data protocol, such as, for example, ISDN, with a digitally modulated wireless service, such as CDMA.

The system 100 consists of two different types of components, including subscriber units 101-1, 101-2, ..., 101-u (collectively the subscriber or mobile units 101) and one or more base stations 170. The subscriber units 101 and base stations 170 cooperate to provide the functions necessary to provide ice wireless data services to a portable computer device 110, such as a laptop computer, laptop computer, personal digital assistant (PDA) or The base station 170 also interacts with the subscriber units 101 to allow transmission of data between the subscriber unit and the public telephone network (PSTN) 180.

More particularly, data and / or voice services are also provided by the subscriber unit 101 of the laptop computer 110, as well as one or more other devices such as telephones 112-1, 112-2 (collectively referred to herein as telephones 112). The phones 112 may themselves in turn be connected to other modems and computers not shown in FIG. 1.1 common ISDN language, the notebook 110 and the telephones 112 are referred to as terminal equipment (TE). Subscriber unit 101 provides the functions referred to as NT-1 (Network Termination Type 1, Network Termination Type 1). The illustrated subscriber unit 101 is particularly intended to operate with a so-called basic rate interface (BRI, Basic Rate Interface), which provides two carrier channels (B channels) and a single data channel

3o (D channel), commonly referred to as 2B + D.

The subscriber unit 101 itself consists of an ISDN modem 120, a device referred to herein as a protocol converter 130 which performs the various functions according to the present invention. the invention, including cheating (spoofing) 132 and bandwidth management (BW-mgt) 134, a CDMA transmitter / receiver 140 and a subscriber unit antenna 150. The various components of the subscriber unit

101 can be realized with discrete devices, or as an integrated unit. For example, an existing standard ISDN modem 120, readily available from a number of manufacturers, can be used with existing CDMA transmitters / receivers 140.1. In this case, the special functions are fully provided by the protocol converter 130, which can be sold as a separate device. Alternatively, ISDN modem 120, protocol converter 130, and CDMA transmitter / receiver 140 may be integrated as a complete unit and sold as a single subscriber unit device 101. Other types of interface connections such as Ethernet or PCMCIA may be used to connect the computer device with the protocol converter 130.

ISDN modem 120 converts data and voice signals between terminal equipment 110 and 112 to a format required by the standard ISDN U interface. The interface is a reference point in ISDN systems, which denotes a point for the connection between the network termination (NT) and the telephone company.

The protocol converter 130 performs cheating 132 and basic bandwidth control functions 134. In general, cheating 132 consists of ensuring that subscriber unit 101 is visible to terminal equipment 110, 112 connected to public telephone network 180 on the other side of base station 170, throughout. time. The bandwidth control function 134 is responsible for allocating and de-allocating CDMA radio channels 160, including controlling the total bandwidth allocated to a given session by dynamically assigning subsets of CDMA radio channels 160 in a manner also described more fully. below.

CDMA transmitter / receiver 140 accepts the data from protocol converter 130, and reformats this data in appropriate form for transmission through a subscriber unit antenna 150 over CDMA radio link 160-1. CDMA transmitter / receiver 140 can operate over only a single radio frequency channel of 1.2288 MHz, or alternatively, in a preferred embodiment, it may be tunable over several such channels.

CDMA signal transmissions are then received and processed by the base station equipment

170. The base station equipment 170 usually consists of multi-channel antennas 171, several

CDMA transmitter / receivers 172 and a bandwidth management feature (bandwidth management, BW-mgt). The bandwidth control 174 controls the allocation of

CDMA radio channels 160 and subchannels, in a manner analogous to the subscriber unit 101. The base station 170 then connects the demodulated radio signals to the public telephone network (PSTN) 180 in a manner well known in the art. Eg. For example, base station 170 can communicate with PSTN 180 over any number of different effective communication protocols, such as primary speed ISDN, or other LAPD-based protocols such as IS-634 or V5.2.

Then proceed briefly with reference to FIG. 1, therefore, the bandwidth control 134 and 174 involve causing the CDMA transmitter / receiver 140 to loop back data bits over the ISDN communication path, to deceive (spoof) the terminal equipment 110, 112 to believe that a sufficiently wide wireless communication link 160 is present all the time. is available. However, it is only when data is actually present from the terminal equipment to the wireless transmitter / receiver 140 that wireless bandwidth is allocated. Therefore, a network layer connection need not allocate the assigned wireless bandwidth throughout the communication session. That is, when data is not presented on the terminal equipment of the network equipment, the bandwidth control function 134 initially allocates radio channel bandwidth 160 and makes it available to another transmitter / receiver and another subscriber unit 101.

It will also be understood that data signals go in two directions over CDMA radio channels 160. Thus, data signals received from PSTN 180 are connected to laptop 110 in so-called forward link direction, and data signals originating from laptop 110 are coupled to PSTN 180 in so called reverse link direction. The present invention particularly involves the way in which a power control mechanism is implemented for the reverse link channels.

To better understand how bandwidth control 134 and 174 achieve the dynamic assignment of radio channels, it will now be seen in FIG. 2. This figure illustrates a possible frequency plan for the wireless forward links 160 according to FIG. invention. In particular, a conventional transmitter / receiver 170 can be tuned, on order, to any channel of 1.2288 MHz within a much larger bandwidth, such as up to 30 MHz. In the case of placement in existing cellular radio frequency bands, these channels are usually made available in the range of 800 to 900 MHz. For personal communication wireless (PCS) systems, channels are typically assigned in the range of about 1.8 to 2.0 GHz. In addition, there are usually two related bands that are active at the same time, separated by a security band, such as

MHz; and the two associated bands form full duplex connections in the forward and reverse directions.

Each of the CDMA transmitters / receivers, such as the transmitter / receiver 140 in the subscriber unit 101, and the transmitter / receivers 172 in the base station 170, are capable of tuning at any given time to a given radio frequency channel. It is generally understood that, for example, a 1.2288 MHz radio frequency carrier at its best provides a total equivalent of continuous transmission with a maximum data rate of about 500 to 600 kbps, within acceptable constraints of bit error rate io To make more efficient use of the available bandwidth, however, each 1.2288 MHz radio channel on the reverse link in a relatively high number of sub-channels. In the illustrated example, the bandwidth is subdivided into 64 subchannels 300, each providing a data rate of 8 kbps. A given subchannel 300 is physically implemented by encoding a transmission with one of a number of different pseudo-random codes and / or code phases that can be assigned. Eg. can the 64 under-.

channels 300 are defined within a single CDMA radio frequency carrier using a different code phase for each defined subchannel 300.

As mentioned above, subchannels 300 are assigned only when necessary, e.g. several subchannels 300 are granted for periods of time where a particular ISDN subscriber unit 101 requests that large amounts of data be transmitted. These subchannels 300 are quickly released during periods of time where subscriber unit 101 is relatively lightly loaded.

The present invention relates in particular to maintaining the reverse connection such that a transmit power level of the subchannels need not be restored each time subchannels are removed and then returned.

Fig. 3 is a diagram illustrating how the subchannels are assigned to the reverse link. It is desirable to use a single radio carrier signal on the reverse link, as far as possible, to limit power consumption, and to preserve the receiver resources that must be made available in the base station. Therefore, a single channel 350 of 1.2288 MHz is selected from the available radio spectrum.

A relatively high number of N, such as 1000 individual subscriber units, is then supported by using a single, long pseudo noise code (pseudonoise, PN) in a special way. First, a number of p phases for the code are selected from 2⁴²-1 available different code phases. The p codephase switches are then used to provide on channel channels. Then each of the sub-channels is further divided into time slots. Therefore, the maximum number that can be supported by subscriber units that can be supported is N, p times s. Using the same PN code with different phases and time slots provides many different subchannels, allowing the use of a single rake receiver in the base station 104.

In the above channel allocation system, radio resources are expected to be allocated based on need. However, one must also take into account the fact that, in order to set up a new CDMA channel, a given reverse link channel must normally be given time not only to achieve code phase locking but also to adapt its transmission to the proper power level. The present invention avoids the need to wait for each channel to achieve this each time it is set up, by means of several mechanisms which are described more fully hereinafter. In general, the technique is to send a maintenance signal of sufficient frequency for each subchannel, even when in standby mode; ie even in the absence of data traffic.

One aim here is to minimize the size of each time slot, which in turn maximizes the number of subscribers that can be maintained in idle mode. The size t of each time slot is determined by the minimum time it takes to guarantee phase locking between the transmitter in the subscriber unit and the receiver in the base station. In particular, a code correlator in the receiver must receive a maintenance or heartbeat signal consisting of at least a certain number of maintenance bits in a given unit of time. As a boundary case, this heartbeat signal is transmitted by transmitting at least one bit from each subscriber unit to each reverse connection at a predetermined time, e.g. its designated time slot on a predetermined of the N subchannels.

Therefore, the minimum time slot duration t depends on a number of factors, including the signal-to-noise ratio and the expected maximum rate of the subscriber unit in the cell. When it comes to signal / noise conditions, this depends

Eb / (No + lO) where Eb is the energy per bit, No is the ambient noise floor, and lO is the interference from other coded transmissions in the other subchannels of the reverse connection that share the same spectrum. Usually, closing the connection requires integration over 8 chip times in the receiver, and 20 times this time is usually required to guarantee detection. Therefore, about 160 chip times are usually required to receive the encoded signal correctly on the reverse link. For a code of 1.2288 MHz, the Tc, chip time, is 813.33 ns, so this minimum integration time is about 130 ps. This, in turn, determines the absolute minimum duration of a data bit, and therefore the minimum duration of a shutter time, t. The smallest shutter time of 130 ps means that a maximum of 7692 time slots can be made available per second for each phase-coded signal.

Once code-phase locking is achieved, the duration of the heartbeat signal is determined by considering the capture or locking range of the code-phase locking circuits in the receiver at the base station. The receiver has e.g. usually a PN code correlator that runs at the code chip rate. An example of such a code correlator uses a delay lock loop consisting of an early / late detector. A loop filter controls this bandwidth's bandwidth, which in turn determines how long the code correlator must be allowed to operate before it can guarantee phase locking. This loop time constant determines how much jitter (jitter) can be tolerated in the code correlator, such as about 1/8 of a chip time, Tc.

In the preferred embodiment, the system 100 is intended to support so-called nomadic mobility. That is, high mobility function in mobile vehicles, as is common in cellular telephony, is not expected to be necessary. The typical user of an active laptop, rather, moves at just a fast speed of about 7.2 km / h. At a speed of 7.2 km / h, which corresponds to a speed of 2 m / sec, a user will move 31 meters at 1/8 of the chip time (Tc) 1 / 1.2288 MHz. It will therefore take about 31 meters divided by 2 meters, or about 15 seconds for such a user to move a distance sufficiently long for him, to a point where the code-phase synchronization loop cannot be guaranteed to remain locked. Therefore, as long as a complete synchronization signal is transmitted on a given reverse connection channel every 15 seconds, the reverse link loop will be maintained. In practice, it is not preferred to push this all the way to the limit, and a sync heartbeat signal is transmitted once for a number of seconds.

Fig. 4 is a state diagram showing a set of operations performed by base station 170 and subscriber units 101. The sequence of states entered into for base station 170 is generally illustrated on the left hand side of the figure, and the state sequence of subscriber unit 101 on the right side.

In a first state 400, the subscriber unit 101 is initialized, such as by turning on its battery power. the subscriber unit 101 then sends a startup message to the base station 170. In this startup state 402, the subscriber unit performs system determination, pilot channel retrieval, synchronization channel retrieval, and other clock control functions such as e.g. specified by the IS-95B air interface standard. In reality, the subscriber unit 101 determines the type of system in which it operates, e.g. a dual mode CDMA or analog mode, obtains the pilot channel acquisition by synchronizing its clock control circuits, and also performs a similar clock control function on the sync channel. In addition, an initial starting value for open loop reverse power level can be determined, such as by measuring a power level received on a forward link, as is known in the art. If the subscriber unit 101 can perform all these tasks within a certain specified time period, it can successfully enter a standby mode state 403.

After initialization, the subscriber unit 101 can inform the base station 120 of its successful completion of such tasks by sending a startup message 430 to the base 170. The base station 120 then enters a state 450 where it assigns a reverse link maintenance channel to the particular subscriber 101. This can be done after acknowledgment of the pilot and synchronization, by sending a code phase p and time slot s to be used for this particular subscriber unit, in a message. Such a message can e.g. is sent on the forward link calling channel which the subscriber unit continues to monitor during its standby mode state 403.

Also, while in the standby state 403, as soon as an open loop power level is established, the subscriber unit 101 periodically enters a state 404 where a heartbeat message is sent to the base station 120 over the reverse connection.

As soon as the base station 170 receives such a heartbeat message, it enters a state 452 where it determines a connection quality metric for the reverse link signal received from the subscriber unit 101.

Then, in state 454, this reverse link quality metric is sent as a link quality report message (LQR) over the reverse link to subscriber unit 101. The LQR message is sent over a call or sync channel since no traffic channel is available during standby mode.

LQR can e.g. contains 8 pieces of information. The link quality metric may be a bit error rate, a noise energy level expressed as Et&gt; / Noi, or a power level.

Upon receiving the LQR, the subscriber unit enters a state 406, where it calculates its reverse power level, using the received LQR and other information.

The subscriber unit then continues to iterate, through states 404 to 407, to maintain an appropriate power level while in standby mode, until the subscriber unit receives a message indicating that it is entering active mode, or otherwise leaving its standby mode. -mode.

On the base station side, states 452, 454 and 456 are similarly repeated for each of the subscriber units which are in standby mode while in idle state.

The heartbeat signal 435 is sent to the synchronization message on the assigned maintenance channel at a data rate which need only be sufficiently fast to allow subscriber unit 101 to maintain synchronization with the base station 170. receiver circuits and base station 170.

In a preferred embodiment, the system is intended to support so-called nomadic mobility. Ie that one does not expect to encounter operation with relatively high mobility, such as in moving vehicles, which is common for cellular telephony. The typical user of a laptop is expected to remain connected only while moving at a fast speed of about 7 km / h. In this situation, a user will move about 30 meters, and 1/8 of the chip time at 1.2288 MHz. Therefore, it takes about 30 meters divided by 2 meters, or about 15 seconds for such a user to move a distance long enough to a point where code-phase synchronization cannot be guaranteed. Therefore, as long as a complete heartbeat signal and power control word for a given reverse link channel is exchanged every 15 seconds, the reverse link will remain at the desired power level for a closed loop.

For further information regarding the event with the heartbeat signal, reference is made to co-existing international application no.

PCT / US99 / 11607 entitled Fast Acquisition of Traffic Channels for a Highly Variable Data Rate, filed May 26, 1999 and assigned to the same licensee as the present invention.

It can now be understood how the present invention implements closed loop power management in a code-shared multi-access system that dynamically assigns reverse link channels, even when such traffic channels are not assigned. This is achieved with the base station determining link quality measurement based on a reverse signal received signal received in response to maintenance heartbeat signals.

The heartbeat signals are transmitted at a frequency that is only sufficiently fast to maintain code-phase locking. In response, a link quality report message is sent back to the subscriber unit on the forward connection, such as on a dial-up or sync channel.

ίο Instead of ISDN, other wiring and networking protocols, such as xDSL (Digital Subscriber Loop), Ethernet or X.25, can be encapsulated, and therefore the dynamic subchannel wireless mapping scheme described here can be advantageously used.