NO338063B1 - Soft handover of a CDMA reverse connection - Google Patents

Description

During the last twenty years, there has been previously incomparable growth in both the type and the demand for wireless communication services. Wireless voice communication services, which include cellular telephones, personal communication services (PCS) and similar systems, now provide almost unlimited coverage. The infrastructure for such networks has been developed to the point where most residents of the United States, Europe and other industrialized areas of the world no longer have just one but several service providers to choose from.

Continued growth in the electronics and computer industry continues to contribute to increasing demand for access to the Internet and the variety of services and opportunities this provides. This widespread use of computer equipment, and in particular those that are portable, and include notebook computers, hand-held personal digital assistants (PDAs), Internet-enabled cell phones and similar devices, has resulted in a corresponding increase in the need for wireless data access.

Although cell phones and PCS networks are deployed on a large scale, these systems were not originally intended to transport data traffic. Instead, these networks have been designed to efficiently support continuous analog signals compared to the digital communication protocols that operate in a burst mode and are necessary for Internet communication. Here one must also take into account that voice communication will work well with a communication channel width of approximately 3 kilohertz (kHz). However, it is generally accepted that for effective Internet communication, such as online skimming, a data rate of at least 56 kilobits per second is required. second (kbps) or higher.

In addition, the nature of data traffic itself is different from the nature of voice communication. Voice requires a continuous two-way connection, i.e. the user at one end of a connection expects to be able to send and receive to the user at the other end of a connection on a continuous basis, and at the same time that the user at the other the end is also able to send and receive. However, access to pages on the Internet is generally very scan-oriented. In the typical case, it is thus the user of a remote client computer who specifies the address of computer files, such as for example on a Web service. This request is then formatted as a relatively short data message, which is usually less than 1000 data words (bytes) long. The other end of the connection, which can for example be a Web server in the network, then responds with the ordered data file which can be from 10 kilobytes to several megabytes of text, images, audio or video data. Due to the Internet's own inherent delays, the user often expects delays that may last a few seconds or more before the ordered content begins to be delivered to the user. Then, once the ordered content has been delivered to the user, the user can read the content page within several seconds or perhaps even minutes before the user indicates the next page to download.

Also, voice networks were built to support high-mobility usage, i.e., long periods of time were used to support mobility that might typically be on a highway or similar to maintain connections as the user of voice-based cellular networks and PCS networks moves at high speed along the highway. However, the typical user of a portable computer is relatively stationary, such as someone who sits at a desk. Thus, the high-speed cell-to-cell mobility considered critical for wireless voice networks is usually not required to support data access.

It should be sensible to retrofit certain components in the existing wireless infrastructures to enable wireless data in a more efficient way. The additional functionality that is implemented for a new class of users who want a data rate but who are users with low mobility should thus be backwards compatible with existing functionality for users who use a low data rate but high mobility. This may make it possible to use the same frequency allocation plans, base station antennas, expansion sites and other aspects of the existing voice network infrastructure that will be used to provide the new high-speed data service.

It will be very important to support as high a data rate as possible on the reverse link in such a network that transports data on the reverse link, for example from the remote unit to the base station. It is taken into account here that the existing digital cell standard such as IS-95 code division multiple access (CDMA) specifies the use of different code sequences in a forward connection direction in order to maintain the least possible interference between channels. In particular, such a system makes use of orthogonal codes on the forward connection, which define the individual logical channels. However, the optimal operation of such a system requires that all codes be time-aligned to a certain limit to maintain orthogonality at the receiver. Therefore, the transfers must be synchronized.

This is not something that needs to be particularly taken into account in a forward connection direction as all transmissions originate from the same location, ie the location of a base transceiver station. However, current digital cellular CDMA standards do not attempt to make use of or require orthogonality between channels in a reverse link direction. It is generally believed that it is too difficult to synchronize transmissions originating in remote devices located at different locations and at potentially very different distances from the base station. Instead, these systems typically use a "chip" level reversal code with unique supplies of these long pseudo-random codes to distinguish the individual reverse link channels. Use of this recasting, however, thus excludes the possibility that different users' broadcasts may be orthogonal in relation to each other.

The present invention relates to a wireless subscriber unit, where the wireless subscriber unit comprises: means for sending a data packet in a soft handover to a plurality of base stations, wherein the data packet is sent using at least one orthogonal code and a pseudorandom noise (PN) code, wherein the plurality of base stations includes a first base station and at least one second base station,

means for receiving a power control command from each of at least two of the base stations, wherein the at least two base stations include the first base station and at least the second base station, and

means for, in response to received power control commands, adjusting a power level associated with the transmission of the data packet, wherein the power level is a lowest power level indicated by one of the power control commands, and wherein only the first base station provides absolute control information for a reverse link channel to the wireless subscriber unit, such that appears from independent claim 1.

Furthermore, the present invention comprises a method for using a wireless subscriber unit comprising: sending, by the wireless subscriber unit, a data packet in a soft handover to a plurality of base stations, wherein the data packet is transmitted using at least one orthogonal code and a pseudorandom noise code, PN, wherein the plurality of base stations includes a first base station and at least one second base station,

receiving, in the wireless subscriber unit, a power control command from each of at least two of the base stations, wherein the at least two base stations include the first base station and the at least second base station;

and in response to received power control commands, adjusting, in the wireless subscriber unit, a power level associated with the transmission of the data packet, wherein the power level is a lowest power level indicated by one of the power control commands, and wherein only the first base station provides absolute control information for a reverse link channel to the wireless subscriber unit , as appears from independent claim 5.

Accordingly, an embodiment of the present invention includes a system that supports communication between participants in a first user group and a second user group. The first group of users, who may be "legacy" users of a digital code division multiple access (CDMA) cellular telephone system, encode their transmissions with a common first code. Such a first user group can be identified in a similar way by providing a unique code phase shift for each user. The other group of users, who may be users of a high-speed data service, encodes their transmissions using the same code and one of the code phase shifts of this code. However, each of the other group's users further encodes their broadcasts with an additional code, the additional code being unique to each of the other group's users. This makes it possible for dispatches from the second user group to be orthogonal to each other while simultaneously maintaining that they appear collectively to be a single user in the first group.

The code assigned to the first user group may be a common "chipping" rate, a pseudo-random code. The code assigned to the second terminal group can typically be a collection of unique orthogonal codes. The individual participants in the first group of terminals may be separated by means of reversal codes which may have unique phase shifts from a selected longer random noise sequence.

In a preferred embodiment, certain steps are taken to ensure proper operation of the signaling among the second user group, or what is called "pulse". In particular, a common code channel can be earmarked for use as a synchronization channel. This enables maintaining the correct timing of the transmissions from the second terminal group, if, for example, the coding scheme is implemented in a reverse connection direction.

In another embodiment, the users in the second group may be assigned specific time slots in which to transmit and therefore maintain orthogonality through the use of time-division multiple access. Again, the point is that the users in the second group collectively appear as a single user for dispatches from the users in the first group.

The principles of the present invention enable current CDMA systems, which are designed for carrier mobility, to support soft handover for orthogonal channel users on their reverse link to increase the robustness of the reverse link channel links in a highly variable RF environment.

Since an orthogonal connection must be timed to maintain orthogonality from one user to the next, use is made of a timing control loop from a single base station. Orthogonality is not easily achieved to two base stations in a reverse connection direction because the relative propagation time delays complicate the timing at both base stations. Therefore, to make use of an orthogonal reverse link in soft handover, there is a primary reverse link base station that provides timing and secondary base stations that can receive the transmissions non-orthogonally.

Special criteria are defined to determine when it is advantageous to reassign the timing from the primary base station to the secondary base station to enable the change of the orthogonality link from the first to the second base station. Even if there is only one orthogonal base station, the signal levels received at the other base station may be sufficient for reception. These signals can be used to enable diversity. This is particularly useful in high mobility systems.

Although only a single base station performs timing control, a preferred one may

embodiment both perform effect management. This is because, as the path loss of the non-orthogonal base station decreases as the user moves, the received power can become so strong that it begins to produce excessive interference, which reduces the secondary base station's capacity. Therefore, when the signal level is sufficient for reception by the secondary base station, commands or messages are sent to the subscriber unit to reduce the transmitted power. Although these commands affect the received power at both the orthogonal base station and the non-orthogonal base station, it may be appropriate to reassign timing control from the primary base station to the secondary base station. A typical condition may be when the measured path loss to the non-orthogonal or secondary base station exceeds a threshold difference which may be, for example, 10 db.

Existing CDMA systems define reverse link channels non-orthogonally. This is accomplished by defining unique spreading code offsets for each reverse connection user. Orthogonal and non-orthogonal backward compatibility can be achieved by orthogonal users for a primary base station sharing the same spreading code. when these user signals are received at other base stations, they are unlikely to be time-aligned, but they will all have unique code offsets and be able to be uniquely identified based on the combination of code offset and orthogonal code. These signals are no more interfering than common non-orthogonal signals which are "old" to existing CDMA systems. Therefore, just as soft handover is performed today, it can be performed with an orthogonal primary base station and non-orthogonal secondary base station.

When the primary base station is reassigned so that timing now comes from a secondary base station (ie, reverse link timing handover has taken place), a significant delay and code phase shift can occur. Using a conventional one-bit differential timing loop may be too slow to quickly achieve orthogonality with the new base station when it is handed over. Therefore, when the handover occurs, a coarse timing adjustment command or message may be used to quickly re-establish the reverse connection, where the coarse timing adjustment may be absolute or relative. In the case of the time management command, the subscriber unit is instructed to make a rough time adjustment, while in the case of the time management message, the subscriber unit responds independently to information in the time management message.

The criteria for time management handover may be based on criteria that include at least the following:

1. the metric for an alternative path exceeds a threshold over a designated period of time,

2. the metric for an alternative path exceeds a threshold in relation to the current path during a designated period of time,

3. the currently selected path falls below an absolute metric, or

4. the candidate path exceeds an absolute metric,

where the metric can be one or more of the following:

a. effect,

b. SNR,

c. effect variance,

d. SNR variance, or

e. the relative ratio of the above metrics between two paths (ie the orthogonal connection and the non-orthogonal connection).

Power control (or SNR control) of an orthogonal reverse link (RL) can be based on both orthogonal (aligned) and non-orthogonal paths. When a non-orthogonal path's SNR meets a quality requirement as specified above while a power control loop is active, the subscriber unit timing may be reassigned to the base station associated with the non-orthogonal path.

Referring to the power control loop, if a command is sent instead of a message or report, the command can be each way's minimum SNR. For example, if two roads are observed, and one needs power while the other has too much power, a command is given to reduce power. This also applies to a soft handover function, where the power output from the subscriber unit is only increased if all commands or messages that deliver power metrics demand that it be increased.

Therefore, there may be a relative offset between commands from a base station's non-orthogonal path and those relating to the orthogonal path. For example, commands requiring more or less power from non-orthogonal pathways may need to be more consistent or apply for a longer time or duration before the orthogonal pathway is ignored and the other pathways control the power reduction. The intrabase station orthogonality zone can be handled in a similar way, as indicated above.

Power control can be maintained from both orthogonal and non-orthogonal base stations while time control orthogonality is controlled by a base station. While power management is maintained for both the orthogonal and non-orthogonal base stations, commands or messages that include metrics must be sent to the subscriber unit transmitter down the forward link.

The power management commands from each base station can be based on whether a quality metric is achieved at each respective base station. This quality metric can be bit error rate, signal-to-noise ratio, received power, or Ec/Io. Provided the metric is satisfied, a transmitter power reduction command can be sent. As the access terminal receives commands from both base stations, it will often receive commands that conflict with each other. When this occurs, the access terminal obeys the command to turn down the power if one occurs. This is in effect an exclusive-OR function, where, for example, a power increase occurs only if both base stations command a power increase. If one of the base stations gives a command for a power reduction, then a power reduction occurs at the access terminal. This will also be the case for multi-bit commands, where the minimum increase or maximum decrease in effect is obeyed.

The aforementioned and other purposes, properties and advantages of the present invention will appear more clearly from the following more specific description of preferred embodiments of the invention, and as illustrated in the accompanying drawings in which like reference numbers indicate the same parts throughout all the different drawings. The drawings are not necessarily made to scale, but instead emphasis is placed on illustrating the principles of the invention, in the accompanying drawings show: Fig. 1 a block diagram of a wireless communication system that supports orthogonal connections and non-orthogonal connections, Fig. 2 is a block diagram of a circuit used by the access terminal shown in fig. 1, Fig. 3 is a block diagram of the circuit shown in Fig. 2 which further includes a code generator to operate on an orthogonal connection with other access terminals, Fig. 4 is a block diagram of the wireless communication system shown in Fig. 1 with several power units making use of orthogonal and non-orthogonal connections, Fig. 5 is a block diagram of a base station processor (BSP) as shown in Fig. 4 with an orthogonal timing controller to control the timing of the access terminals on the orthogonal link, Fig. 6A is a network diagram for the network shown in Fig. 4 with an alignment controller located in the base station processors, FIG. 6B is a network diagram of the network shown in FIG. 4 with an alignment controller located in the field unit, Fig. 6C is a network diagram of the network shown in Fig. 4 with an alignment controller which is placed in a base station controller, Fig. 7 is a flow chart for processes that can be used by the base terminal station and the access terminals shown in fig. 4 to make signals mutually orthogonal, Fig. 8 is a flowchart for processes that can be used by the base terminal stations and the access terminals in the multi-cell environment shown in fig. 4 for soft handover, and Fig. 9 is a flowchart for processes that can be used by the base terminal stations and the access terminals shown in fig. 1 for power management.

Then follows a description of preferred embodiments of the invention.

Fig. 1 is a block diagram of a code division multiple access communication system 10 (CDMA system) employing a signal coding scheme in which a first class of logical channels is assigned unique long codes with different code phase shifts, and a second class of logical channels provided by of a common code and common code phase shift, combined with an additional coding process that makes use of a unique orthogonal code for each channel.

In the following detailed description of a preferred embodiment, the communication system 10 is described such that the shared channel resource is a wireless channel or radio channel. However, it can be understood that the techniques described here can be applied to implement shared access to other types of media such as telephone connection, data network connection, cable connections and other physical media to which access is granted on a demand-driven basis.

The system 10 supports wireless communication for a first group of users 110 as well as a second group of users 210. The first group of users 110 are typically "old" users of cellular telephone equipment such as wireless handsets 113-1, 113-2, and/or cell mobile tele -phones 113-h which are installed in means of transport. The first user group 110 mainly uses the network in a speech mode whereby their communications are coded as continuous transmissions. In a preferred embodiment, these users' transmissions are conveyed from the subscriber unit 113 through the forward link via radio channels and reverse link radio channels 50. Their signals are managed at a central location that includes a base station antenna 118, a base transceiver station (BTS) 120, base station controller (BSC) 123. The first user group 110 is therefore typically engaged in voice conversations using the mobile subscriber units 113, BTS 120 and BSC 123 to connect telephone connections through the public switched telecommunications network (PSTN) 124. The forward connection 40 in use by the first user group may be encoded in accordance with well-known digital cellular standards such as the Code Division Multiple Access (CDMA) standard defined in IS-95B and specified by the "Telecommunications Industry Association" (TIA). This forward link 40 includes at least one uplink channel 141 and a traffic channel 142, as well as other logical channels 144. These forward link channels 40 of "old" type 141, 142, 144 are defined in such a system using orthogonally coded channels. These first user groups 110 also encode their transmissions over the reverse link 50 in accordance with the IS-95B standard. They therefore make use of several logical channels in a reverse connection direction 50, which includes an access channel 151, the traffic channel 142 and other logical channels 154.1 this reverse connection 50 codes the first user group 110 usually the signals with a common long code that makes use of different code phase shifts. This way of encoding signals for "old" users 110 on the reverse connection 50 is also well known in the art.

The communication system 10 also includes a second user group 210. This second user group 210 is typically users who require high-speed wireless data services. Their system components include a number of remote personal computer devices (PC devices) 212-1, 212-2,... 212-h, ... 212-1, corresponding remote subscriber access units (SAU) 214-1, 214 -2, .... 214-h, .... 214-1, and associated antennae 216-1, 216-2, ...., 216-h, .... 216-1. Centrally located equipment includes a base station antenna 218 and a base station processor (BSP) 220. This BSP 220 provides connections to an Internet gateway 222, which in turn provides access to a data network such as the Internet 224, and the network file server 230 which is connected to the network 222.

These PCs 212 can send data to and receive data from the network 230 through bidirectional wireless connections that are implemented over the forward connection 40 and the reverse connection 50 that are used by the "old" users 110. It should be understood here that in a point- to multipoint multiple access wireless communication system 10 as shown, a given base station processor 220 supports communication with a number of different active subscriber access units 214 in a manner similar to that of a cellular telephone communication network.

In the present scenario, the radio frequencies allocated for use by the first group 110 are the same as those allocated for use by the second group 210. The present invention relates in particular to how to allow a different coding structure to be used by the second group 210 while minimal interference is created for the first group 110.

The PCs 212 shown are typically lap computers 212-1, handheld devices 212-h, Internet-enabled cellular telephones, or personal digital assistant (PDA) types of computing devices. These PCs 212 are each connected to a respective SAU 214 through a suitable wired connection such as an Ethernet type connection.

A SAU 214 allows its associated PC 212 to be connected to the network filter 230 through the BSP 230, the gateway 222 and the network 224.1 the reverse connection direction, i.e., for data traffic going from the PC 212 to the server 230, the PC 212 delivers an Internet Protocol level packet (IP ) to this SAU 214. This SAU 214 then encapsulates the wired framing (ie the Ethernet framing) with appropriate wireless link framing and coding. The duly formatted wireless data packets then travel over one of the radio channels included in the reverse link 50 through the antennas 216 and 218. At the central base station location, the BSP 220 then extracts the radio link framing, reformats the packet into IP form and forwards it through the Internet gateway 222. The packet is then routed through any number and/or any type of TCP/IP network, such as, for example, the Internet 224 , to its final destination, such as, for example, the network file server 230 .

Data may also be transmitted from the network file server 230 to the shown PCs 212 in a forward connection direction 40. In this case, an Internet Protocol packet (TP packet) originating at file servers 230 travels through the Internet 224, and through the Internet gateway 222 and arrives at the BSP 220 Appropriate wireless protocol framing and encoding is then appended to the IP packet. The packet then travels through the antenna 218 and 216 to its intended receiver SAU 214. The receiving SAU 214 decodes the wireless packet format, and forwards the packet to PC 212 which performs IP layer processing.

A given PC 212 and the file server 230 can therefore be considered the endpoints of a duplex connection at the IP level. As soon as a connection is established, the user of PC 212 can therefore transfer data to and receive data from the file server 230.

From the perspective of the second user group 210, the reverse connection 50 in reality consists of a number of different types of logical and/or physical radio channels which include an access channel 251, several traffic channels 252-1, ..., 252-t and a maintenance channel 53. The reverse connection access channel 251 is used by the shown SAU 240 to send messages to the BSP 220 to request that they be granted traffic channels. The assigned traffic channels 252 can then carry payload data from SAU 214 to BSP 220. It should be understood here that a given IP layer connection can actually have more than one traffic channel 252 assigned to it. In addition, a maintenance channel 253 may transport information such as synchronization and power control messages to further support transmission of information over the reverse link 50.

Similarly, the second user group has a forward connection 40 which includes a call channel 241, several traffic channels 242-1, ... 242-t and the maintenance channel 243. The call channel 241 is used by the BSP 220 not only to inform the SAU 214 that it has been allocated forward connection traffic channels 252, but also to inform the SAU 214 about allocated traffic channels 252 in the reverse connection direction. The traffic channels 242-1, . 214. It should be understood here that there are usually many more traffic channels 241 than paging channels 241 or maintenance channels 243. In the preferred embodiment of the present invention, the logical forward connection channels 241, 242 and 243 and 251, 252 and 253 are defined by assigning each channel a pseudorandom noise channel code (PN code). The system 10 is therefore a so-called code-divided multiple-axis system (CDMA system) in which several coded channels can make use of the same radio frequency channel (RF channel). The logical or coded channels can also be further divided or allocated among several active SAU 214.

The sequence of signal processing operations is typically performed to encode the respective reverse link 50 logical channels 51, 52 and 53.1 reverse link direction the transmitter is one of the shown SAU 214 and the receiver is a base station processor (BSP) 220. The preferred embodiment of the invention is implemented in an environment in which " "legacy" users of CDMA digital cellular telephone systems such as one operating in accordance with the IS-95B standard are also present on the reverse link 50.1 an IS-95B system, reverse link CDMA channel signals are identified by assigning non-orthogonal pseudo-random noise codes (PN- codes).

Attention is now directed to fig. 2, where the channel coding process for the first group of "old" users 110 will be described in more detail. This first class of users includes, for example, digital CDMA cellular phone users who encode signals in accordance with the IS-95B standard mentioned above. The individual channels are therefore identified by modulating the input digitized speech signal with a pseudorandom noise code sequence (PN sequence) for each channel. More specifically, the channel coding process takes an input digital signal 302 that represents the information to be transmitted. A quadrature modulator 304 provides an in-phase (i) and quadrature (q) signal path for a pair of multipliers 306-i and 306-1. A short pseudorandom noise code generator (PN generator) 305 provides a short (in this case a 2 15-1 or 32767 bits) code length that is used for spread spectrum purposes. The short code is therefore typically the same code for each of the logical channels for the first group 110.

A second code modulation step is applied to the (i) and (q) signal paths by multiplying the two signal paths by a further long PN code. this is achieved by means of the long code generator 307 and the long code multipliers 308-i and 308-q. The long code serves to uniquely identify each user on the reverse connection 50. The long code can be a very long code, which is, for example, only repeated every 2 42-1 bits. The long code is used at the short code "chipping" rate, for example a bit of the long code is applied to each bit issued by the short code modulation process, so that further spectrum spreading does not occur.

Individual users are identified by applying different phase shifts of the PN long code for each user.

It should be understood here that other synchronization steps must also be done for the first user group 110. More specifically, these transmissions on the reverse connection 50 are constructed so that they are asynchronous and therefore they are not necessarily perfectly orthogonal.

Fig. 3 provides a more detailed look at the channel encoding process for the second group of users 210. This second group 210 includes, for example, wireless data users who encode signals in accordance with a format optimized for data transmission.

The individual channels are identified by modulating the input data with a pseudo-random noise code sequence (PN code sequence) which is the same code sequence used for the first user group 110. However, as will soon be appreciated, the channels in the second group 210 are uniquely identified by of special orthogonal codes such as Walsh code. More specifically, the channel coding process for the second user group 210 has an input data signal 402 and applies a number of codes generated by a short code generator 405, Walsh code generator 413 and long code generator 407.

As a first step, a quadrature modulator 404 supplies an in-phase (i) and quadrature (q) signal path to a first pair of multipliers 406-i and 406-q. The short random noise code generator (PN code generator) 405 provides a short, in this case a code of length 215, which is used for spread spectrum purposes. This short code is therefore the same as the short PN code used for each of the channels in the first group 110.

A second step in the process is to apply an orthogonal code such as that generated by Walsh code generator 413. This is accomplished by multipliers 412-i and 412-q which "impregnate" the orthogonal code on each of the i-phase and the quadratic-sig-nal roads. The orthogonal code assigned to each logical channel is different, and uniquely identifies such channels.

In a final step in the process, a second pseudorandom noise long code (PN long code) is applied to the (i) and (q) signal paths. The long code generator 407 thus conveys the long code to a respective one of the in-phase multiplier 408-i and the quadrature multiplier 408-q. This long code does not uniquely multiply each user in the second group 210. More specifically, this code can be one of precisely the same long codes that are used in the first group which uniquely identifies its first user groups 110. Thus, it is used in the same way for for example, a short code "chipping" clock code such that one bit of the long code is used for each bit emitted by the short code modulation process. In this way, all the users in the second group 210 appear as a single "old" user in the first group 110. However, the users in the second group 210 can be uniquely identified given that they have been assigned unique orthogonal Walsh codes.

Since the implementation in the preferred embodiment is on a reverse link 50, additional information must be provided to maintain orthogonality among the different users in the second group 210. In particular, therefore, a maintenance channel 243 is included in the forward link 40. This maintenance channel or "pulse" channel provides synchronization information and /or other timing signals so that the remote units 214 can synchronize their broadcasts properly. The maintenance channel may be time-locked. For more details on the formatting of this forward connection maintenance channel 243, reference is made to co-pending US Patent Application No. 09/775,305 filed on February 1, 2001 and entitled

"MAINTENANCE LINK USING ACTIVE/STANDBY REQUEST CHANNELS".

It should be understood that some infrastructure can therefore be shared by both the second user group 210 and the first user group 110. For example, the antennas 218 and 118 may be a shared antenna, even if they are shown as separate base station antennas in fig. 1. Similarly, the location of the antennas can therefore be the same. This enables the second user group 210 to share equipment and physical site facilities that are already present and in use by the "old" users 110. This significantly simplifies the deployment of wireless infrastructure for this new user group 210, for example as there is no need to develop new installation sites and antenna systems.

Fig. 4 is a network diagram corresponding to that shown in fig. 1.1 this wireless network 400 provides a first base station processor (BSP) 220-1 and a second base station processor 220-2 (collectively shown as 220) access to other networks (eg, the Internet or PS TN) for the access terminals 213-1, 213-2 , .... 213-3 and handheld units 113-1, 113-2 and 113-3. The base station processors 220 also support soft handover of CDMA reverse connections using orthogonal channels for "new" access terminals 213, while at the same time enabling "old" handheld devices 113 to make use of reverse connections in a normal manner. Access terminals 213 and the hand-held units 113 are alternately referred to as field units or subscriber access units

(SHEEP).

"Old" field devices means field devices that are not equipped with a modulation process that uses unique orthogonal codes to share a common reverse link channel with other field devices. "New" field units means field units provided with a modulation process that uses unique orthogonal codes to share a common reverse link channel with other field units. The shown BSPs support soft handover by selectively reallocating the timing of reverse link channels based on criteria. In a preferred embodiment, both BSPs 220 supply power control feedback to the field devices.

By continued reference to fig. 4, above the antenna towers 218 are first and second timing charts 403-1 and 403-2 (collectively 403) illustrating the relative timing of reverse link signals for each of the field units communicating with the respective base station processors 220. The timing charts 403 illustrate a separation between orthogonal reverse link channels that are time-aligned and orthogonal or non-orthogonal channels that are not time-aligned. As discussed above, each of the "new" access terminals 213 sharing a common reverse link channel has an additional coding process to add a unique orthogonal code to distinguish its reverse link signals from the reverse signals of other network devices using the common reverse link channel.

For purposes of this discussion, it is assumed that (i) the access terminals 213 share an orthogonal common reverse link channel and (ii) the three handheld units 113 use "legacy" non-orthogonal reverse link communication techniques.

In the first timing diagram 403-1, the first base station processor 220-1 uses an alignment controller (not shown) to align the timing of orthogonal reverse link channels for the access terminals controlled by the BSP-220-1.1 in this case, the BSP 220-1 controls the timings in the logical the reverse connection channels 420-1 and 420-2, which are represented by the vertical time stamps 425-1 and 425-2, for the first field unit 213-1 and the second field unit 213-2, respectively. Reverse link channels that have their reverse links time aligned (ie, phase aligned common long codes) are referred to as "native" orthogonal channels 410. The third access terminal 213-3 which is also in communication with the first base station processor 220-1 does not have its logical reverse link channel 420-3 (425 -3) timed with the logical reverse connection channels of the first and second access terminals 213-1 and 213-2. The third access terminal 213-3 has its reverse connection channel 420-3 controlled by the second BSP 220-2. Accordingly, the timings of the logical reverse connection channel 420-3 (425-3) of the third field unit 213-3 are shown shifted in the first timing diagram 403-1 relative to the native orthogonal channels 425-1 and 425-2.

In the second timing diagram 403-2, the logical reverse connection channels 420-1, 420-3, 420-4, 420-5 and 420-6 are to the five wireless network devices 213-1, 213-3, 113-1, 113-2 and 113-3 in communication with the second base station processor 220-2 represented by vertical timestamps 425-1, 425-3, 425-4, 425-5 and 425-6 respectively. The second BSP 220-2 determines the timing for the third access terminal 213-3 orthogonal reverse connection 420-3 (425-3), but not for any of the other access terminals 213-1, 213-2. Therefore, as expected, the reverse logic connections 420 (425) are out of phase relative to each other at the second BSP 220-2, as indicated in the second timing diagram 403-2. Three of the reverse connection channels 425-1, 425-5 and

425-6 are relatively close to each other in time at the second BSP 220-2 and are referred to as "foreign" orthogonal channels 415.

The foreign orthogonal channels 415 are not truly orthogonal as these channels

do not have unique orthogonal codes that distinguish one from another on a common reverse link channel. Therefore, the foreign orthogonal channels 415, if aligned, would destructively interfere with each other at the second BSP 220-2.1 a special situation, each of the base station processors 220 may support native orthogonal channels 410 and foreign or non-orthogonal channels 415. This situation indicates that a combination of "new" and "old" field units may be used within the same cell zone.

In existing orthogonal technology, there is no soft handover technique in the reverse connection when a field unit, such as one of the access terminals (for example 213-3), moves from a cell zone belonging to a first base station processor 220-1 to a cell zone belonging to a second base station processor 220-2. The reverse link soft handover technique described herein (i) supports communication in the reverse link from "legacy" wireless network devices 213 to multiple base station processors 220, (ii) performs time management and power management (will be described later), and (iii) coordinates it by the multiple base station processors 220 to be the "leader" of the reverse link timing for a field unit based on criteria, as described with reference to FIG. 8. By coordinating the one of the several BSPs 220 that will determine the timing of the reverse connection channel to a given access terminal 213, the given access terminal 213 can move from one cell zone to another cell zone without loss of the connection in the reverse connection. The principles of the present invention also include a technique for fast orthogonal time alignment (i.e. adjusting the phase of the common logical channel's long code for an access terminal 213 so that the common reverse connection channel is time-aligned, or mutually orthogonal, with the common reverse connection channel of other access terminals 213).

The base station processor 220 receiving control of the timing of the reverse link channel determines a coarse offset of the timing of the field unit's logical reverse link channel as a function of the timing of the logical reverse link channel of other field units sharing the same logical reverse link channel. The rough displacement is sent to the field unit 213 in the form of a displacement command or displacement message. On the basis of the coarse offset information, the field makes a coarse time control adjustment of the logical channel in accordance with the coarse time control offset. After the coarse time management adjustment, a fine time management adjustment may be made in accordance with fine time management offsets that may be measured by the base station processor 220 after the coarse time management adjustment of the logical reverse link channel 420. Fig. 5 shows a block diagram of one of the base station processors 220-1 which includes facilities for soft handover of a CDMA reverse link which utilizes an orthogonal channel structure. The base station processor 220-1 receives reverse link channels from the field units 113, 213 via the antenna tower 218. A receiver 505 receiving a reverse link channel from a given field unit 213 sends the received signal to an orthogonal timing controller 510. The orthogonal timing controller 510, or an equivalent unit, determines a coarse timing offset 513 with respect to to reverse link channels from other field devices sharing the same logical reverse link channel. The coarse time control offset 513 can be an absolute target for dispatch to a given field unit 213 in the form of a command or can be a relative target and be sent back to a given field unit 213 in the form of a message, the given field unit 213 making use of additional pro- sessing to determine the time shift (ie the phase alignment) of the reverse link signal. A combination of absolute and relative goals can also be used. Fig. 6A is a schematic representation of the network having the first base station processor 220-1 and the second base station processor 220-2. The base station processors 220 include respective alignment controllers 515. The alignment controllers 515 are used by the base station processors 220 to select or control the base station processor 220 that will control the time alignment of the reverse links 420 for the field units 213.

To determine which of the aforementioned BSPs 220 will control the time alignment for the field device 213-1, the alignment controllers 515 may calculate a metric (eg, signal-to-signal-to-noise ratio (SNR)) associated with the signal that has been received from field unit 213-1.

A given alignment controller 515 may issue a message to other alignment controllers 515 to notify the other base station processors 220 that the associated base station processor 220 associated with a given alignment controller 515 shall determine the timing of the reverse link channel to the field unit 213-1. Alternatively, the given alignment controller 515 may issue a message or a command to another alignment controller such as the alignment controller 515 in the second base station processor 220-2, that the second base station processor 220-2 should determine the timing of the reverse link channel to the field unit 213-1. Other negotiation solutions may also occur between the alignment controllers 515 to determine which of the base stations 220 will control the alignment of the field unit 213. As soon as a base station processor 220 has been commanded to or has been selected to control the timing of the orthogonal reverse link channel, the orthogonal timing controller 510 is used to determine a rough time management offset, as has been discussed above, to enable ear time management control over delivery.

Fig. 6B is a schematic representation of the wireless network in which alignment controller 515 is deployed as part of field unit 213-1, and in this case incorporated into subscriber access unit 214-1. Alternatively, alignment controller 515 may be included in PC 212-1 or may be an independent unit which is electrically connected to subscriber access unit (SAU) 214-1 or PC 212-1.

In this arrangement, the alignment controller 515 provides a command or message to the SAU 214-1 at the field unit 213-1 to cause the field unit 213-1 to respond to a timing control signal received from either the first base station processor 220-1 or the second base station processor 220 -2.

Fig. 6C is a schematic representation of the wireless network 400 in which the alignment controller 515 is deployed in the base station controller (123). In this case, the alignment controller 515 may receive information from each of the orthogonal timing controllers 510 from the first base station 220-1 or the second base station 220-2 to determine which of the base station processor 220 will control the timing of the orthogonal reverse link channel from the field unit 213-1. The alignment controller 515 may make this determination based on a number of different factors, such as the signal-to-noise ratio of the reverse link signal at each of the base station processors 220. The alignment controller 515 may make use of commands or messages to indicate that of the base station processor 220 which shall control the timing of the reverse link of the field unit 213-1.1 in any case, the selected base station processor 220 may issue a command or message to the field unit 213-1 that it is the base station processor 220 that will control the timing of the orthogonal reverse link channel. It is to be understood here that the alignment controller 515 can also understand the diversity concept and make choices with respect to that of the base station processor 220 which shall control the timing of the reverse connection channel in order to thus maximize the diversity efficiency between the base station processors 220.

Fig. 7 is a flowchart for a soft handover process of a CDMA orthogonal reverse connection in accordance with the principles of the present invention. In this example, the first base station processor 220-1 performs a first process 700, and the access terminal 213 performs a second process 735. After the BSP process 700 starts in step 705, the BSP process 700 waits to receive a reverse connection signal in step 710 from the access terminal 213. After access terminal process 735 starts in step 740, access terminal 213 transmits in step 745 a reverse connection signal with the unique orthogonal code on a reverse connection channel common to reverse connection signals from other access terminals 213. BSP process 700 receives the reverse connection signal in step 710 and continues in step 715.1 step 715, the BSP process 700 determines whether the long code, which identifies the access terminal 213 as belonging to an orthogonal reverse connection group, in the reverse connection signal is in phase with the long codes from other access terminals 213 in the same access terminal group, as described with reference to FIG. 2 and 3. It is the long codes, and not the unique, specific, orthogonal codes, such as Walsh codes, that are time-aligned with the base station processor 700. The unique, identifying codes of the reverse link signals are mutually orthogonal when the long codes are phased.

If the long code in the reverse link signal is in phase (ie, time-aligned) with other reverse link signals with long codes from other access terminals 213 in the same mutually orthogonal reverse link group, process 700 stops at step 730. If the long code is not in phase with the long codes in reverse link signals from other access terminals, the BSP process 700 continues in step 720, where a determination of the coarse time control offset is made using the orthogonal time controller 510, as discussed above with reference to fig. 5.

The BSP process 700 continues in step 725, where the base station processor 220 sends the coarse timing offset to the access terminal 213 in the form of a command or message. The access terminal process 735 receives the coarse timing offset and adjusts the timing of the reverse link signal in step 750. The access terminal process 735 ends in step 755, and the BSP process 700 ends in step 730.

Fig. 8 is a flowchart for the two base station processors 220-1 and 220-2 as they interact with the access terminal 213. The first base station processor 220-1 performs a process 800 which controls the timing of the access terminals 213's reverse connection. The second base station processor 220-2 performs a process 802 which provides processing that does not control the timing of the access terminal 213 reverse connection. The access terminal 213 performs its own process 833. The process 833 is able to receive feedback, and make adjustments to the timing of the reverse link signal in coarse and fine amounts, and to make power level adjustments in accordance with power level feedback received from the base station processors 220.

The access terminal 213 sends signals (at step 836) which are received by the first base station processor 220-1 and the second base station processor 220-2. In this example, it is assumed that the first base station processor 220-1 has previously been selected to control the timing of the reverse link signal by the access terminal 213 The first base station processor 220-1 thus receives the orthogonal reverse connection signals (step 803) from the access terminal 213 which are either arranged with other reverse connection signals that share the same reverse connection channel or which are to be arranged with other reverse connection signals from other access terminals 213 that make use of the same reverse connection channel. The base station processor 220-1 determines whether the signal from the access terminal 213 meets a time criterion or criteria in step 806. If the signal does not meet a time criterion or criteria, the process 800 determines a coarse timing offset that is fed back to the access terminal 213 to align the signal with other signals that do use of the same code. The reverse link is received by the access terminal 213 in step 839. If the signal meets the timing criterion or criteria, process 800 continues in step 809, where process 800 determines whether a fine time shift is required. If the answer is yes, the processor 800 sends to the access terminal 213 what is the fine time offset, which is received in step 839 by the process 833 performed by the access terminal 213. If no fine time control offset is required, the process 800 continues in step 815.

In step 815, the base station processor 220-1 determines whether the power level in the signal emitted by the access terminal 213 should be adjusted. Similarly, the second base station processor 220-2 also determines whether to cause a power level adjustment in step 815 for the access terminal 213. In any case, the power level shifts are sent to the access terminal 213 in the forward connection.

If no power level adjustment is required, referring to both the first base station processor process 800 and the second base station processor process 802, the respective processes proceed to step 818, where it is determined whether timing control handover should be initiated. Time management control handover can be initiated based on a set of criteria:

(a) the metric in an alternative path exceeds a threshold in a pre-specified period of time;

(b) the metric of an alternative path exceeds a threshold relative to the current one

road in a predetermined period of time,

(c) the currently selected path falls below an absolute metric, and (d) the candidate path exceeds an absolute metric, where the metric may be one or more of the following:

(a) effect,

(b) SNR,

(c) power variance,

(d) SNR variance, and

(e) the relative relationship of the two roads.

If an initiation of timing control handover has occurred, then, in step 821, the base station processor 220-1 updates other base station processors and the base station controller 123. The access terminal 213 may also be informed of the timing control handover. If the timing control has not been handed over, processes 800 and 802 continue in step 824, where a decision is made to release or accept the timing control if another base station processor 220, base station controller 123, or access terminal 213 sends a command or message to the base station processor 220 to that it will control the timing of the reverse connection signal. If the base station processor releases or accepts timing control commitments, processes 800, 802 continue at step 830 to update system operating parameters; otherwise, the processes 800, 802 continue back to step 803 to receive signals from the access terminals 213.

The process 833 performed by the access terminal 213 receives feedback in step 839 and processes the feedback as follows. First, if no feedback is received, the process 833, in this embodiment, enters a loop waiting for feedback in step 839. If feedback is received, the process continues in step 842 to determine whether a coarse timing adjustment command has been received or Message. If the answer is yes, the rough time adjustment is made in step 845. It should be understood here that the rough time control adjustment can be an absolute or relative target, as has been described above.

In step 848, the access terminal 213 determines whether a fine timing adjustment command or message has been received. If the answer is yes, the fine timing adjustment is made in step 851. It should be understood that the fine timing adjustment is usually a differential command or message. After the fine timing adjustment, the process 833 determines whether a power level adjustment command or message has been received. If the answer is yes, the access terminal 213 adjusts the power level in step 857.

After the timing or power adjustments, the process 833 updates the operational parameters in the access terminal 213 in step 860. After updating the system parameters, the process 833 repeats in step 839, where one waits for feedback from one or more base station processors 220.

Fig. 9 is a flowchart for the processes 900, 920 that are performed by the base station processors 220 and the access terminal 213, respectively, to adjust the power level in the reverse connection signal that is transmitted by the access terminal 213. With reference to the processes 900 that are performed by the base station processors 220, the processes 900 begin in steps

905.1 step 910 the base station processors 220 determines whether it should cause the access terminal 213 to change the power level of the reverse connection signal in step 910. If the change of the reverse connection signal power level is desired, feedback is sent to the access terminal 213 in the form of a command or message. The base station processor's 220

process 900 ends at step 915.

Process 920 performed by access terminal 213 begins in step 925. Once feedback is received in step 930, process 920 continues in step 935, where a determination is made as to whether all base station processors 220 know of a power level increase. If the answer is yes, process 920 continues at step 940, where the access terminal 213 increases the power level of the reverse link signal by as much as the lowest increment feedback message. If not all of the base station processors 220 request a power level increase, it is determined in step 945 whether any of the base station processors 220 request a power level reduction. If the answer is yes, then in step 950 the access terminal 213 reduces the power level as much as the lowest reduction feedback. Process 920 ends at step 955, or may simply loop back to step 930 to wait to receive a power level feedback.

Although power control is maintained to both the orthogonal and non-orthogonal base stations, commands and metrics may be sent to the subscriber base transmitter (ie, the access terminal 213) via a forward link. Power control commands from each base station processor 220 may be based on whether a signal quality metric is achieved at each respective base station processor 220. This signal quality metric may be, for example, a bit error rate (BER), a signal-to-noise ratio (SNR), received power, or Ec/Io . Provided that the metric is satisfied, a command can be issued to reduce the transmitted power. As the access terminal 213 receives commands and messages from both base station processors 220, it will often experience command conflicts. When this occurs, the access terminal 213 intercepts the "reduced power" command. This is effectively an exclusive-OR function, for example a "power up" occurs if both base station processors 220 command power up. If one of the base station processors 220 commands a power reduction, a power reduction occurs. This is also the case for multi-bit commands, where the minimum increase or maximum decrease of power is obeyed.

Claims (8)

1. A wireless subscriber unit, comprising: means for sending a data packet in a soft handover to a plurality of base stations, wherein the data packet is sent using at least an orthogonal code and a pseudorandom noise code, PN, wherein the plurality of base stations includes a first base station and at least a second base station , means for receiving a power control command from each of at least two of the base stations, wherein the at least two base stations include the first base station and at least the second base station, and means for, in response to received power control commands, adjusting a power level associated with the transmission of the data packet, wherein the power level is a lowest power level indicated by one of the power control commands, characterized in that the first base station provides absolute control information for a reverse link channel to the wireless subscriber unit. 2. Wireless subscriber unit as set forth in claim 1, wherein the first base station is a primary base station, and at least the second base station is one or more secondary base stations. 3. Wireless subscriber unit as set forth in claim 1 further comprising: means for sending data packet in soft handover to two or more base stations, and means for receiving the power control commands from the two or more base stations. 4. Wireless subscriber unit as set forth in claim 1 further comprising: means for receiving power commands from the plurality of base stations, wherein the power commands include a multi-bit power command and a single-bit power command, wherein the multi-bit power command indicates a plurality of power levels and the single-bit power command indicates at least one power reduction . 5. A method of using a wireless subscriber unit comprising: transmitting, by the wireless subscriber unit, data packet in a soft handover to a plurality of base stations, wherein the data packet is transmitted using at least an orthogonal code and a pseudorandom noise code, PN, wherein the plurality of base stations includes a first base station and at least one second base station, receiving, in the wireless subscriber unit, a power control command from each of at least two of the base stations, wherein the at least two base stations include the first base station and the at least second base station, and in response to received power control commands, to adjust in the wireless subscriber unit a power level associated with the transmission of the data packet, wherein the power level is a lowest power level indicated by one of the power control commands, characterized in that only the first base station provides absolute control information for a reverse link channel to the wireless subscriber unit. 6. Method according to claim 5, in which the first base station is a primary base station, and at least the second base station is one or more secondary base stations. 7. Method according to claim 5, further comprising: that the wireless subscriber unit sends a data packet in a soft handover to two or more base stations, and the wireless subscriber unit receives the power control commands from the two or more base stations. 8. The method of claim 5, further comprising: receiving in the wireless subscriber unit power commands from the plurality of base stations, wherein the power commands include a multi-bit power command and a single-bit power command, wherein the multi-bit power command indicates a plurality of power levels and the single-bit power command indicates at least a power reduction .