Maintenance link using active/standby request channels

Abstract

Multiple field units in a CDMA system are synchronized for communication with a base station using shared forward and reverse link channels. In an illustrative embodiment, each field unit is assigned a time slot in a forward link channel to receive messages from the base station. Likewise, each field unit is assigned a time slot on a common reverse link channel for transmitting messages to the base station. Timing alignment and power level control among each of many field units and the base station is achieved by analyzing messages received at the base station in a corresponding time slot as transmitted by each field unit. Thereafter, a message is transmitted from the base station in a corresponding time slot to a particular field unit for adjusting its timing or power level so that future messages transmitted from the field unit are received in the appropriate time slot at the base station at a desired power level. In this way, minimal resources are deployed to maintain communication and precise synchronization between a base station and each of multiple users, minimizing collisions between field units transmitting in adjacent time slots on the reverse link. This method reduces the frequency a field unit must rely on the use of a slotted aloha random access channel according to IS-95.

Description

RELATED APPLICATION [0001] This application is a continuation of application Ser. No. 09 / 775,305, filed Feb. 1, 2001, which claims the benefit of U.S. Provisional Application Ser. No. 60 / 180,598 filed on Feb. 7, 2000. The entire teachings of the above applications are incorporated herein by reference.BACKGROUND OF THE INVENTION [0002] Increasing use of wireless telephones and personal computers has led to a corresponding increase in demand for advanced telecommunication services that were once thought practical only for specialized applications. In the 1980s, wireless voice communication became widely available through cellular telephone networks. Such services were thought at first to be for the exclusive province of businessmen because of expected high subscriber costs. The same was also true for access to remotely distributed computer networks, whereby until very recently, only business people and large institutions could afford the necessary computers and wireline access equipme...

AI Technical Summary

Benefits of technology

[0014] In one application, a forward link channel is partitioned to include both “active” and “standby” time slots, where an active time slot is assigned to a field unit to indicate that reverse link traffic channels are presently being used for transmitting a data payload to the base station in the reverse link. A standby time slot is assigned to a field unit for maintaining synchronization with the base station even though the corresponding field unit is not presently transmitting a data payload over the reverse link. Consequently, a field unit in the standby mode can immediately transmit on newly assigned reverse link channel without a prolonged delay of re-synchronizing since the field unit is already synchronized with the base station.

[0035] Another aspect of the present invention involves a novel method of providing a minimal feedback loop for supporting timing alignment between the base station and each of multiple field units. The base station analyzes a marker incorporated in each message received in an assigned time slot to detect whether a field unit message directed to the base station is early or late with respect to a preferred timing with respect to the base station. A message such as a single advance / retard control bit is then transmitted back to the corresponding field unit to advance or retard its timing so that future message transmissions from the field unit are received at the base station in the appropriate time slot. Thus, multiple field units transmitting messages on the shared reverse link channel generally do not interfere with each other when transmitting in adjacent time slots. Additionally, the timing information sent on the forward link enables the field unit to synchronize itself to the base station for receiving messages in its assigned time slot on the forward link. As a consequence of maintaining each of multiple synchronized links, a corresponding field unit can immediately transmit a data payload in a reverse link direction without having to go through a lengthy process of re-synchronizing with the base station prior to a data transmission.

Problems solved by technology

Such services were thought at first to be for the exclusive province of businessmen because of expected high subscriber costs.

There still is no widely available satisfactory solution for providing low cost, high speed access to the Internet, private intranets, and other networks using the existing wireless infrastructure.

First, the typical manner of providing high speed data service in the business environment over a wireline network is not readily adaptable to the voice grade service available in most homes or offices.

For example, such standard high speed data services do not necessarily lend themselves to efficient transmission over standard cellular wireless handsets because wireless networks were originally designed only to provide voice services.

Although wireline networks were known at the time when cellular systems were initially developed, for the most part, there was no provision made for such wireless systems to provide higher speed ISDN- or xDSL-grade data services over cellular network topologies.

This is quite dissimilar to the traditional environment supporting data transmissions in which the wireline medium is relatively inexpensive and is not typically intended to be shared.

Therefore, even though such users may remain connected to the Internet or private intranet continuously during an entire day, actual use of the high speed data link is usually quite sporadic.

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